Safety assessment of cocamidopropyl betaine, a cosmetic ingredient

Abstract

Cocamidopropyl betaine (CAPB) is a surfactant derived from coconut oil that is widely used in cosmetics and personal products for several purposes, such as a surfactant, foam booster, mildness, and viscosity control. Cocamidopropyl betaine is used at concentrations up to 30% in cosmetics. The acute toxicity, skin irritation, eye irritation, skin sensitization, repeated dose toxicity, genotoxicity, carcinogenicity, and phototoxicity of cocamidopropyl betaine were evaluated. Cocamidopropyl betaine was observed to induce mild skin irritation, eye irritation and skin sensitization. The NOAEL of cocamidopropyl betaine was determined to be 250 mg/kg/day based on the results of a 92-day repeated-dose oral toxicity study in rats. The systemic exposure dose of cocamidopropyl betaine was estimated to range from 0.00120 to 0.93195 mg/kg/day when used in cosmetic products. The margin of safety of cocamidopropyl betaine was calculated to be greater than 100 when used at a maximum concentration of 6% in leave-on products and 30% in rinse-off products, suggesting that its use in cosmetic products is safe under current usage conditions.

Introduction

Cocamidopropyl betaine is derived from coconut oil and is used as a synthetic surfactant and foam booster that is commonly used in personal care, cosmetics, and cleaning products. It is known for its mildness and ability to produce rich lather products, such as shampoos, body washes, liquid soaps, and other cosmetic and toiletry items. The chemical structure of cocamidopropyl betaine is shown in Fig. 1. The chemical formula for cocamidopropyl betaine is typically C₁₉H₃₈N₂O₃. It is an amphoteric surfactant, which means it has both a positively charged (cationic) and a negatively charged (anionic) part of its structure. This amphoteric nature allows it to function as a surfactant and contribute to the foaming and cleaning properties of various personal care and cleaning products.

Fig. 1.

Summary of the toxicities of cocamidopropyl betaine (CAPB). Cocamidopropyl betaine (CAPB) induces mild irritation in the skin and eyes and slight contact skin sensitization. CAPB exhibits relatively low oral toxicity based on the results of 90-day repeated dose toxicity experiments. No genotoxicity, carcinogenicity, or phototoxicity effects were observed for CAPB. LD50: lethal dose 50, NOEL: no observed effect level

Cocamidopropyl betaine is generally considered to be a safe ingredient with a low toxicity profile and is widely used in the cosmetics and personal care industries. However, there have been some concerns regarding its safety, including skin and eye irritation and allergic reactions. Here, we reviewed the toxicity of cocamidopropyl betaine, performed an exposure assessment, and determined the risk of its use in cosmetic products.

Physical and chemical properties

Cocamidopropyl betaine is a synthetic surfactant derived from coconut oil. The IUPAC name for cocamidopropyl betaine is 2-[3-(dodecanoylamino)propyl-dimethylazaniumyl]acetate [1]. The Chemical Abstracts Service (CAS) number is 61789-40-0, and the molecular formula is C₁₉H₃₈N₂O₃ [1]. Table 1 shows the chemical identity of the cocamidopropyl betaine in detail. Cocamidopropyl betaine is chosen for its mildness and ability to create stable lathers and effectively clean in personal care and cleaning products. These properties make it a versatile ingredient in a wide range of products, including shampoos, body washes, and liquid soaps. The specific physical and chemical properties of a particular formulation may vary depending on the product and its intended use. The detailed physical and chemical properties of cocamidopropyl betaine are shown in Table 2. Cocamidopropyl betaine is a pale yellow to amber liquid or solid depending on its formulation and temperature. It typically has a mild, characteristic odor. Cocamidopropyl betaine is easily soluble in water and can create clear or slightly hazy solutions [2]. Cocamidopropyl betaine has a complex chemical structure consisting of both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. Cocamidopropyl betaine has both positively charged (cationic) and negatively charged (anionic) functional groups in its chemical structure, which contributes to its amphoteric nature. This structure allows it to function as a surfactant by lowering the surface tension between the oil and water, making it effective for cleaning and foaming. Its pH is typically close to neutral, which makes it suitable for a wide range of personal care products. The density of cocamidopropyl betaine can vary depending on its concentration and form (liquid or solid). Cocamidopropyl betaine is generally considered biodegradable, meaning that it can break down in the environment over time. However, the biodegradability of products containing cocamidopropyl betaine may depend on the overall formulation and other ingredients present.

Table 1.

Physical and chemical properties of cocamidopropyl betaine

Identity	Contents	Refs.
INCI name	Cocamidopropyl betaine	[37]
Chemical name
IUPAC name	2-[3-(Dodecanoylamino)propyl-dimethylazaniumyl]acetate	[1]
Synonyms	Cocamidopropyl dimethyl glycine Cocoyl amide propylbetaine Cocoyl amide propyldimethyl glycine Cocoyl amide propyldimethyl glycine solution	[1]
CAS No	61789-40-0	[32]
EC No	263-058-8/274-923-4	[37]
Molecular formula	C19H38N2O3	[1]
Physical form	Clear, pale-yellow liquid	[38]
Molecular weight	342.5 g/mol	[38]
Solubility	Water; 2 g/10 mL at 25℃ Alcohol; 2 g/10 mL at 25℃	[38]
Boiling point	230℉ (110 °C)	[38]
Melting point	No data available	–
Density	1.053 g/cm3 at 20 °C	[38]
Viscosity	36.383 mm2/s (static) at 20 °C	[38]
Flash point	95 °C at 101 325 97.94 kPa	[38]

Table 2.

Summary of acute toxicity studies of cocamidopropyl betaine (CAPB)

Subjects	Route	Dose	Results	Refs.
Mouse/CFR (10/group)	Oral intubation	30% active CAPB	LD50 = 6.90 g/kg	[4]
Rat/Wistar (5 females and 5 males/group)	Oral gavage	5.00, 6.30, 7.94, 10.00 mL/kg of CAPB (30% active, pH 5.5)	LD50 = 7.97 g/kg	[5]
Rat/Albino (5/group)	Oral gavage	2.0, 4.0, 5.0, 6.3, 8.0, 16.0 g/kg of 30% active CAPB	LD50 = 4.9 g/kg	[6]
Rat/Wistar (5 females and 5 males/group)	Oral gavage	2.0, 2.71, 3.68, 5.0, 6.78 g/kg of 30% active CAPB	LD50 = 4.91 g/kg	[7]
Rat/Sprague‒Dawley (5 females and 5 males/group)	Oral gavage	35.61% active CAPB	LD50 > 1.8 g/kg (male)	[8]
Rat/CD (5 females and 5 males/group)	Oral gavage	5.0 g/kg of 31% active CAPB	LD50 > 5.0 g/kg	[8]
Rat/Wistar (5/group)	Oral gavage	4.0, 8.0, 10.0, 12.5, 16.0, 32.0 g/kg of 30% active CAPB	LD50 = 8.55 g/kg	[8]
Rat/CD (5 females and 5 males/group)	Dermal	2.0 g/kg of 31% active CAPB	LD50 > 2.0 g/kg	[8]

Functions and uses of cocamidopropyl betaine in cosmetics and noncosmetics

Cocamidopropyl betaine is a versatile ingredient used in cosmetics, primarily because of its surfactant properties. As a surfactant, it helps to reduce the surface tension of liquids, making it easier to mix water with oils and dirt. This property allows for effective cleansing and removal of makeup, impurities, and excess oils from the skin. It acts as a foam booster, producing a rich and stable lather in cosmetic products such as facial cleansers, body washes, and shampoos. The lathering effect enhances the sensory experience of using these products and can help in spreading the product evenly. Furthermore, cocamidopropyl betaine can function as an emulsifying agent. This approach helps stabilize emulsions, which are mixtures of oil and water. This property is particularly useful in cosmetic creams and lotions, where it helps ensure that the oil and water-based ingredients remain well mixed. It can be used to control the thickness or viscosity of cosmetic products, which affects their texture and feel on the skin. This characteristic is important in the formulation of creams and lotions, allowing for better spreadability and absorption. Cocamidopropyl betaine is known for its mildness and is often used in products designed for individuals with sensitive or easily irritated skin. Compared with harsher surfactants, this approach helps reduce the potential for skin irritation. In hair care products, cocamidopropyl betaine can help reduce the amount of static electricity in hair, increasing the ease of management and styling. Some formulations may incorporate cocamidopropyl betaine to provide a conditioning effect on the hair or skin. Cosmetic products that commonly contain cocamidopropyl betaine include facial cleansers such as foaming cleansers and makeup removers; bath products such as body washes and shower gels; hair care products such as shampoos and conditioners; liquid hand soaps; creams and lotions; and sunscreen formulations. The versatility and mildness of cocamidopropyl betaine make it a popular choice in the cosmetics industry because of the wide range of products available for cleaning and caring for the skin and hair. The frequency of use data provided by industry to the U.S. FDA in 2010 indicated that cocamidopropyl betaine was used in 2743 cosmetic products. In 2010, cocamidopropyl betaine was utilized at concentrations ranging from 0.005% to 11% [3].

Cocamidopropyl betaine’s multifunctional properties, including its mildness and ability to create a stable lather, make it a valuable ingredient in a wide range of noncosmetic products designed to clean, sanitize, and care for various surfaces and objects. It is particularly popular in applications where effective cleaning is essential, such as in kitchens, bathrooms, and personal care and hygiene products. Noncosmetic applications for cocamidopropyl betaine include liquid soaps and hand sanitizers, dishwashing detergents, laundry detergents, surface cleaners, car wash products, industrial cleaners such as degreasers and floor cleaners, agricultural and horticultural products such as pesticides and herbicides, pet shampoos and conditioners, and pet grooming products such as ear cleaners and paw cleaners.

Toxicity identification of cocamidopropyl betaine

Acute toxicity

The oral LD₅₀ of 30% active cocamidopropyl betaine in albino rats was determined to be 4.9 g/kg. The dermal LD₅₀ in CD rats was greater than 2 g/kg. The acute toxicity studies are summarized in Table 2.

CFR mice (10 per group) were administered cocamidopropyl betaine solution (30% active) by gastric intubation [4]. The oral lethal dose (LD₅₀) of cocamidopropyl betaine in mice was reported to be 6.90 g/kg [4]. Ten (5 female, 5 male) Wistar rats per group were orally treated with 5.00, 6.30, 7.94, or 10.00 mL/kg of cocamidopropyl betaine (30% active) [5]. The oral LD₅₀ was calculated to be 7.97 g/kg. Rats in all dosage groups exhibited clinical symptoms such as a decrease in motor activity, disrupted coordination, abnormal body posture, cyanosis, diarrhea and a decrease in body temperature during first 24 h starting approximately 20 min after administration. All the surviving rats exhibited a normal appearance and behavior [5]. Five Albino rats (5 per group) were administered cocamidopropyl betaine (30% active) at doses between 2.0 and 16.0 g/kg by gavage [6]. Sluggishness, diarrhea, nasal hemorrhaging, and moisture in the vicinity of the hindquarters were observed with severity increasing with higher doses. Based on these results, the oral LD₅₀ for cocamidopropyl betaine (30% active) solution in rats was determined to be 4.9 g/kg [6]. Furthermore, Sprague‒Dawley rats (5 females and 5 males per group) received cocamidopropyl betaine (30% active) at doses of 2.0, 2.71, 3.68, 5.0, or 6.78 g/kg via gavage [7]. The acute oral LD₅₀ of full-strength cocamidopropyl betaine (30% active) was 4.91 g/kg [7]. According to the American Chemistry Council report, The acute oral LD₅₀ was > 1.8 g/kg for 35.61% active cocamidopropyl betaine in male Sprague‒Dawley rats and was to be greater than 5.0 g/kg for 31% active cocamidopropyl betaine in CD rats [8]. Another study of the American Chemistry Council reported that the acute oral LD₅₀ was determined to be 8.55 g/kg for 30% active cocamidopropyl betaine in Wistar rats [8].

According to an acute dermal toxicity study reported by the American Chemistry Council, the acute lethal dermal dose of cocamidopropyl betaine (31% active) exceeded 2.0 g/kg [8]. CD rats (five males and five females) received 2.0 g/kg of cocamidopropyl betaine (31% active) on the clipped surface of the dorsolumbar region (occluded). After a 24 h period, the dressings were removed, followed by washing the area with warm water and subsequent drying. The study revealed no unexpected deaths or clinical signs of systemic toxicity. Additionally, no abnormalities were recorded at necropsy [8].

Eye irritation

When the concentration of active cocamidopropyl betaine was adjusted to 4.5%, mild conjunctival irritation occurred in the unrinsed eyes, while in the rinsed eyes, the irritation was minimal. The eye irritation studies are summarized in Table 3.

Table 3.

Summary of eye irritation studies of cocamidopropyl betaine (CAPB)

Subjects	Dose	Results	Refs.
Albino Rabbit (n = 3/group)	4.5% active CAPB, 0.1 mL	Unrinsed eyes: slight conjunctival erythema and chemosis in all 3 eyes Rinsed eyes: very slight conjunctival irritation in 2 of 3 eyes	[39]
Albino Rabbit (n = 3)	30% active CAPB, 0.1 mL	Mild conjunctival erythema, chemosis, and discharge Diffuse corneal opacity Slight iritis	[40]
Albino Rabbit (n = 3)	6% active CAPB, 0.1 mL	Mild conjunctival erythema and slight discharge	[41]
New Zealand White Rabbit (n = 6)	7.5% active CAPB (pH 8.3), 0.1 mL	Mild-to-moderate conjunctival irritation Moderate corneal opacity in 1 eye	[42]
Albino Rabbit (n = 1)	10% active CAPB (pH 6.1), 0.1 mL	Draize score 28 after day 1, 25 after day 2, 30 after day 3, 14 after day 4, 7 after day 7	[43]
New Zealand White Rabbit (unrinsed: n = 6; rinsed: n = 3)	30% active CAPB, 0.1 mL	Unrinsed eyes: corrosive (corneal opacity, slight iritis, conjunctival irritation, necrosis), mean eye irritation score 32.5 ± 4.4 after 24 h, 31.7 ± 3.3 after 48 h, 41.7 ± 11.7 after 72 h, 27.2 ± 11.4 after 7 days (scale 0–110) Rinsed eyes: minimal irritation (mean score = 10.0 + 2.0 after 24 h)	[44]
New Zealand White Rabbit (n = 9)	10% active CAPB, 0.1 mL	Unrinsed eyes: moderately irritating, mean eye irritation scores 25.7 ± 8.3 after 24 h, 16.7 ± 10.9 after 48 h, 9.3 ± 11.4 after 72 h, 0 by day 7 Rinsed eyes: nonirritating, mean score of 2.0 ± 2.0 after 24 h, 0 by 48 h	[45]
New Zealand White Rabbit (n = 6)	5% CAPB, 0.1 mL	Not an irritant Draize score = 4.90	[46]
New Zealand White Rabbit (n = 6)	10% CAPB, 0.1 mL	Moderately irritating Draize score = 27.3	[48]
Albino Rabbit (n = 6)	3.0% active CAPB	Corneal irritation scores: 0 on days 1 and 2, 1.66 on days 3 and 4, 4.16 on day 7 (max. score = 80) Iritis score: 8.33 on day 1, 4.16 by day 7 (scale 0–10) Conjunctival irritation score: 15.37 (scale 0–20), 6 by day 7	[49]
Albino Rabbit (n = 6)	3.0% active CAPB	No corneal irritation Iritis score: 5 on day 1, 0 by day 7 (scale 0–10) Conjunctival irritation score: 14.33 (scale 0–20), 0 by day 7	[49]
Albino Rabbit (n = 6)	3.0% active CAPB, 0.1 mL	An eye irritant Mean ocular index: 41.6 (max. 110)	[50, 51]
New Zealand White Rabbit (unrinsed: n = 6; rinsed: n = 3)	Soap formulation containing 2.3% active CAPB, 0.1 mL	Moderately irritating to iris and conjunctiva Unrinsed eyes: average irritation score = 18.7 Rinsed eyes: average irritation score = 20.0	[52]
New Zealand White Rabbit (unrinsed: n = 6; rinsed: n = 3)	Soap formulation containing 2.3% active CAPB	Unrinsed eyes: minimally irritating, average irritation score = 1.7 (max. 110) Rinsed eyes: mildly irritating, average irritation score = 3.3	[53]
New Zealand White Rabbit (n = 4, rinsed)	Soap formulation containing 6.5% active CAPB, 0.1 mL	Moderately irritating Mean corneal irritation score: 13.8, 18.8, 11.3, 5, 1.3 after 1 h, 24 h, 48 h, 72 h, and 7 days (max. 80) Mean iridial irritation score: 3.8 after 1 and 24 h, declining to 0 after 7 days Mean conjunctival irritation score: 11, 7.5, 4, 3.5, 2 after 1 h, 24 h, 48 h, 72 h, and 7 days Total mean irritation score = 30.0 (max. 110)	[54]
Albino Rabbit (n = 6)	Formulation containing 6.0% active CAPB, 0.1 mL	Conjunctival irritation: mean score 4 (max. 20) after day 1 No corneal irritation or iritis	[10]

Skin irritation

An undiluted solution of cocamidopropyl betaine at full strength of 30% active ingredient, exhibited mild irritant properties in rabbits. However, cocamidopropyl betaine with 50% dilution demonstrated nonirritant characteristics. The skin irritation studies are summarized in Table 4.

Table 4.

Summary of skin irritation studies of cocamidopropyl betaine (CAPB)

Subjects	Dose	Results	Refs.
Albino Rabbit (n = 3)	50% diluted 1:1(v/v) CAPB,	Not a primary irritant	[55]
Albino Rabbit (n = 6)	30% active CAPB	Primary irritation index (PII) = 0.5 Mild primary irritant Very slight erythema	[56]
Albino Rabbit (n = 3)	7.5% active CAPB solution	No irritation	[57]
Albino Rabbit (n = 1)	10% active CAPB solution, pH 6.1	PII = 0.25 No irritation	[43]
Rabbit (n = 6)	10% active CAPB solution, pH 4.5	PII = 0.3 Very slight erythema	[58]
New Zealand White Rabbit (n = 6)	30% active CAPB	PII = 3.75 Eschar formation	[59]
Albino Rabbit (n = 3)	15% active CAPB solution	PII = 3.5 Not a primary irritant Well-defined erythema Slight edema	[60]
Human (n = 10)	- Two soap formulations of 1.9% active CAPB - Cumulative occulsive patches for 21 days	Total irritation scores: 588 and 581 Primary irritants	[9]
Human (n = 19)	- 0.06% CAPB) - A single occulsive patch	No irritation	[10]
Human (n = 12)	- 0.52% CAPB - Occulsive patches for 5 days	Erythema score: 0.48 (scale 0–4)	[10]

In a cumulative irritation study, each skin site on the backs of 10 volunteers was treated with 0.3 mL of two soap formulations containing cocamidopropyl betaine (1.9% active) using occlusive patches [9]. These patches were applied daily for 23 h over 21 consecutive days. The total skin irritation scores for 21 applications of two formulations for all subjects were 588 and 581, indicating that the formulations were primary irritants to human [9].

In a single insult occlusive patch test, 0.06% cocamidopropyl betaine was applied to 19 panelists [10]. Of the 19 panelists, 15 did not show any irritation, while 4 reported a score of irritation. Based on these results, the cocamidopropyl betaine formulation was considered to be practically nonirritating [10].

A group of 12 human participants were subjected to daily applications of 0.2 mL of a 0.52% cocamidopropyl betaine solution in a liquid soap formulation using occlusive patches on the participants' forearms for 5 days. Following the application, an erythema score was calculated as 0.48 (scale 0–4) [10].

Skin sensitization

Although cocamidopropyl betaine was suspected as a contact allergen [11], it was suggested that impurities in cocamidopropyl betaine products may be responsible for allergic reactions. Contaminations of amidoamine and dimethylaminopropylamine (DMAPA) in cocamidopropyl betaine solution may be responsible for the skin sensitizing potential. Thus, it is advised that patients who are positive for amidoamine or DMAPA should avoid products containing cocamidopropyl betaine.

In a Magnusson-Kligman maximization test, no evidence of delayed contact hypersensitivity or sensitization was observed when 10% or 7.5% active cocamidopropyl betaine solution were topically administered to Pirbright White guinea pigs. However, microscopic alterations were observed in the treated skin of albino guinea pigs, indicating a slight delayed-type contact sensitization reaction when exposed to a 30% active cocamidopropyl betaine solution, as determined by the maximization test and modified Draize test. A summary of the results from the skin sensitization studies is presented in Table 5.

Table 5.

Summary of skin sensitization studies of cocamidopropyl betaine (CAPB)

Subjects	Dose	Results	Refs.
Guinea pig (n = 15)	- Induction: (1) 0.05% active CAPB (2) 6% active CAPB - Challenge: 1% active CAPB	No evidence for delayed contact hypersensitivity	[12]
Guinea pig (n = 20)	- Induction: 0.75% active CAPB - Challenge: 0.01875% CAPB	No evidence of sensitization	[13]
Guinea pig/Albino(n = 20)	- Induction: (1) 0.03% active CAPB or 0.03% active CAPB) plus the adjuvant (2) 3% active CAPB - Challenge: 3% active CAPB	Erythema, edema, acanthosis, mild intracellular edema, lymphomononuclear infiltration (8/20) acanthosis, mild intracellular edema, a moderate lymphomononuclear infiltration (4/20) Slight acanthosis (2/20)	[14]
Guinea pig (n = 20)	- Induction: 0.15% active CAPB - Challenge: 0.015% active CAPB	Delayed-type contact sensitization	[14]
Human (n = 88)	- Open application HRIPT - 1.872% active CAPB	No sensitization	[15]
Human (n = 93)	- Open application HRIPT - 0.93% active CAPB	No sensitization	[16]
Human (n = 100)	- HRIPT - 0.3% active CAPB	No sensitization	[17]
Human (n = 141)	- HRIPT - 1.5% active CAPB increased to 3.0% active	No sensitization	[18]
Human (n = 210)	- HRIPT - 6% active CAPB	No sensitization	[19, 20]
Human (n = 27)	- HRIPT - 0.018% active CAPB	No sensitization	[21]
Human (n = 781 or 102)	- Patch test - 1% or 0.3% active CAPB	56/781 positive (7.2%) 3/102 positive (3%)	[22]
Human (n = 10,798)	- Patch test - 1% or 0.3% active CAPB	29 positive (0.27%)	[23]
Human (n = 12)	- Patch test - CAPB % unknown	Irritation only	[24]
Human (n = 93)	- Patch test - 1% or 0.3% active CAPB	4 positive	[60]
Human (n = 210)	- Patch test - 1% or 0.3% active CAPB	12 positive (5.75%)	[26]

In another maximization test, fifteen male Pirbright White guinea pigs received 0.1 mL of 50% aqueous solution of Freund complete adjuvant at the first pair of sites on their clipped dorsoscapular region [12]. At the second pair of sites, 0.1 mL of cocamidopropyl betaine (0.05% active) in sterile isotonic saline was administered. At the third pair of sites, 0.1 mL of cocamidopropyl betaine (0.05% active) in a 1:1 mixture of isotonic saline and Freund complete adjuvant was applied. One week later, an occlusive 48-h induction patch containing cocamidopropyl betaine (6% active) was applied to the same area. All animals were exposed to a single occlusive 24-h challenge patch containing cocamidopropyl betaine (1% active). The study found no evidence of delayed contact hypersensitivity [12].

A delayed contact hypersensitivity test for a formulation containing cocamidopropyl betaine (0.75% active) was conducted using 20 albino guinea pigs [13]. Closed patches containing the test solution (0.4 mL) were applied to a shaved area. After 6 h, the patches were removed, followed by rinsing the area with warm water. This procedure was repeated for thesubsequent 2 weeks at the same site. The animals were left untreated for 2 weeks prior to the primary challenge test. The challenge test involved the application of 0.01875% cocamidopropyl betaine (a 2.5% solution of 0.75% active cocamidopropyl betaine) to a freshly clipped skin site that had not been previously treated for 6 h. The responses after 24 and 48 h showed no evidence of sensitization [13].

A maximization test and a modified Draize test were conducted for cocamidopropyl betaine formulation in albino guinea pigs [14]. The first group received intradermal injections of Freund complete adjuvant alone, the second group received the cocamidopropyl betaine sample (0.03% active), and the third group received the cocamidopropyl betaine (0.03% active) along with the adjuvant. After one week, a 48-h occlusive induction patch containing the cocamidopropyl betaine (3% active) was applied topically. After three weeks, single 24-h occlusive patches were applied to the clipped flanks of all animals. The left flank received the cocamidopropyl betaine (3% active), and the right flank received water. At necropsy, 8 out of the 20 test animals showed erythema and edema after the challenge application. Microscopic examination revealed epidermal acanthosis, inter- and intracellular edema, and significant infiltration of lymphocytes, monocytes, and a few eosinophils into the superficial layers of the dermis. Four other animals exhibited less prominent microscopic lesions, including acanthosis, mild intracellular edema, and moderate lymphomononuclear infiltration of the superficial dermis. The remaining two animals exhibited slight acanthosis [14]. The same laboratory conducted another experiment involving a 0.15% active cocamidopropyl betaine solution for induction and 0.015% active cocamidopropyl betaine for challenge with the same assay. Among the 20 test animals, 6 displayed slight erythema and edema upon macroscopic examination. Microscopically, slight acanthosis was observed. The investigators concluded that commercially supplied cocamidopropyl betaine has the potential to cause delayed-type contact sensitization [14].

A repeated open application procedure using1.872% cocamidopropyl betaine was conducted to assess skin sensitization in 88 human volunteers [15]. For the induction phase, the volunteers were treated three times a week for three weeks. Challenge patches were simultaneously applied to both the induction and alternate arms. The areas were evaluated 24, 48, and 72 h after removal, following a 6-h period of exposure. No sensitization was observed in any of the 88 participants [15].

Another test was conducted using a 0.93% active aqueous solution of cocamidopropyl betaine in 93 individuals [16]. The induction agents were administered at the same location and the sites were evaluated after a 48-h period. For the challenge test, a different site was used and assessed after 48 and 96 h. Of the participants, 10 had mild reactions to the test substance. These responses were determined to be a result of primary irritation rather than sensitization, both during the induction and challenge tests [16].

Hill Top Research, Inc., performed a similar study on a formulation containing cocamidopropyl betaine (0.3% active) with 100 human volunteers [17]. No evidence of sensitization was observed [17].

Human applicants (n = 141) participated in the study on skin sensitization to cocamidopropyl betaine (1.5% active) [18]. The concentration was increased to 3.0% active cocamidopropyl betaine. Participants who joined the study one week earlier received two applications at the 1.5% concentration, while all subsequent applications utilized the 3.0% concentration. During the induction phase, patches were applied to the same untreated site on the participants' backs three times per week for three consecutive weeks. The patches were removed after 24 h. After a period of 10 to 15 days without treatment, the challenge patch was applied to a previously untreated site for 24 h. No reactions were observed during either the induction or challenge phases [18].

In a study by Clinical Research Laboratories, a repeat insult patch test (RIPT) was performed to assess skin sensitization caused by cocamidopropyl betaine (6% active) in cleansing cloths [19, 20]. This study involved two groups of participants, with 104 participants completing the study in phase I and 106 participants in phase II. A 1/2 inch square of the test material was applied to the upper back in a semioccluded patch for 24 h. A total of nine induction patches were utilized. Following a 2-week resting period, challenge patches were applied to a new area on the back. No adverse reactions were observed in either of the participant groups [19, 20].

Researchers at KGL, Inc., performed a study on the potential for skin sensitization with 0.018% active cocamidopropyl betaine solution in 27 participants [21]. During the induction phase, the participants were pretreated with 0.05 mL of a 0.25% aqueous solution of sodium lauryl sulfate (SLS). After the SLS patch was removed, 0.05 mL of cocamidopropyl betaine (0.018% active) was applied to the same site. The induction occlusive patch remained for 48 h. This induction patch procedure was repeated for a total of five exposures. Following a 10-day rest period, the participants were exposed to 0.05 mL of a 5% SLS solution for 1 h before receiving the challenge patch of cocamidopropyl betaine on the opposite side of the body. The challenge patch was occluded for 48 h. No adverse reactions were observed during either the induction or challenge phases. These findings indicated that the utilization of a facial cleanser containing 0.018% active cocamidopropyl betaine is unlikely to cause contact sensitivity reactions under normal usage conditions [21].

In a study performed by de Groot et al., two groups of patients were examined to test the occurrence of cocamidopropyl betaine allergy [22]. The first group consisted of 781 patients, primarily individuals suspected of having occupational contact dermatitis; 217 hairdressers were included. These patients underwent patch testing with various allergens, including 1% aqueous cocamidopropyl betaine. The second group, consisting of 102 patients suspected of having cosmetic dermatitis, underwent patch testing with 1% aqueous cocamidopropyl betaine. In the first group, 56 patients (7.2%) had positive reactions to cocamidopropyl betaine, with 17 classified as having definite cases, all of whom had used shampoos and/or shower gels containing the substance. Among these 17 patients, eight were hairdressers who experienced dermatitis on their hands. In the second group, only three patients (3%) had a positive reaction to cocamidopropyl betaine, all of whom had been using shower gels, shampoos, and/or body lotions containing this substance. The study documentation did not specify whether the administered cocamidopropyl betaine concentration was 1% active or 1% aqueous (equal to 3% active) [22].

Armstrong et al. performed a patch testing study on patients suspected of having contact dermatitis [23]. The patients were subjected to testing using a standard series containing either 1% aqueous cocamidopropyl betaine. Out of the 10,798 patients subjected to testing, 29 (0.27%) exhibited a positive reaction to cocamidopropyl betaine. Among these 29 patients, 23 presented cases deemed relevant, as they reported dermatitis on their face, neck, hands, or across widespread areas. The authors suggested that the use of higher-purity cocamidopropyl betaine was related to a reduced incidence of sensitization to this substance. However, the study documentation did not provide information on whether the administered cocamidopropyl betaine concentration was 1% active or 1% aqueous (equal to 3% active) [23].

In a double-blind randomized controlled study, the allergenicity of coconut oil derivatives was evaluated with 10 control participants and 12 participants who had previously been diagnosed with an allergy to cocamidopropyl betaine [24]. Of the 12 participants, three showed doubtful reactions to this substance during the patch test. One control participant also showed a doubtful reaction to cocamidopropyl betaine. Based on these findings, the authors of the study proposed that these doubtful reactions are more likely to be irritant reactions than allergic reactions [24].

A study assessing skin allergy to cocamidopropyl betaine was performed in 706 patients [25]. Of 706 patients, 93 (83 women and 10 men) were temporarily diagnosed with cosmetic contact dermatitis. Four individuals had positive reactions to a 1% aqueous solution of cocamidopropyl betaine. Specifically, two participants experienced scalp itching and erythema on their foreheads, ears, and necks after using shampoos containing cocamidopropyl betaine. The other two participants developed eczema on their faces and/or necks following the use of face cleansers containing cocamidopropyl betaine. The study documentation did not provide sufficient information to determine whether the concentration of cocamidopropyl betaine administered was 1% active or 1% aqueous (0.3% active) [25].

Fowler performed a patch testing study on 1% aqueous cocamidopropyl betaine solution in addition to the North American Contact Dermatitis Group (NACDG) series in 210 patients who were suspected of having allergic contact dermatitis to cosmetics and toiletries [26]. Twelve individuals (5.7%) showed a positive reaction to cocamidopropyl. Among the 12 individuals, seven were determined to have cases with definite relevance, as their reported dermatitis was cleared after the use of products containing cocamidopropyl betaine was discontinued. The study documentation did not provide information on whether the administered cocamidopropyl betaine concentration was 1% active or 1% aqueous [26].

Repeated dose toxicity

The repeated oral dose toxicity studies are summarized in Table 6.

Table 6.

Summary of repeated dose oral toxicity studies of cocamidopropyl betaine (CAPB)

Subjects	Route/Period	Dose	Results	Refs.
Sprague- Dawley Rat (n = 10/sex/group)	Oral gavage/ 92 days (daily)	0, 250, 500, or 1000 mg/kg/day	Nonglandular gastritis in 6 male and 3 female rats in the 1000 mg/kg/day group, 2 male and 2 female rats in the 500 mg/kg/day group, not in the 250 mg/kg/day dose group (microscopic evaluations) NOEL: 250 mg/kg/day	[8]
Sprague- Dawley Rat (n = 8/sex/group)	Oral gavage/ 28 days	100, 500, 1000 mg/kg/day (30.6% active CAPB)	No clear relationship between dose and mortality	[27]
Sprague- Dawley Rat	Oral gavage/ 28 days (5 days/week)	0, 250, 500, or 1000 mg/kg/day	Edema in the mucosa of the nonglandular stomach in 1000 mg/kg/day group NOEL: 500 mg/kg/day	[8]

Crl:CF(SD)BR Sprague–Dawley rats (10/sex/group) were subjected to daily oral gavage administration of cocamidopropyl betaine (specific concentration not specified) in distilled water at doses of 0, 250, 500, or 1000 mg/kg/day for a period of 92 days, with a dosage of 10 mL/kg per day. Microscopic evaluations revealed nonglandular gastritis in six male and three female rats in the 1000 mg/kg/day group, as well as in two male and two female rats in the 500 mg/kg/day group. However, this effect was absent in the 250 mg/kg/day dosage group. The NOEL for this subchronic study of cocamidopropyl betaine in rats was determined to be 250 mg/kg/day [8].

Groups of eight male and eight female Sprague–Dawley rats were administered a full-strength cocamidopropyl betaine solution (30.6% active) [27]. These rats received dosages of 100, 500, and 1000 mg/kg/day via gavage for a minimum period of 28 days. Mortality was greater in the treated groups than in the control group, but no clear relationship between dose and mortality was noted. All rats in the 100 mg/kg group showed similar responses to those in the control group [27].

In a 28-day short-term oral toxicity study, 0, 250, 500, or 1000 mg/kg/day cocamidopropyl betaine was administered by gavage to male and female Sprague–Dawley rats [8]. No treatment-related deaths or decreases in food or water consumption were found during the study. No treatment-related effects were observed in the hematological assessments, clinical chemistry, ophthalmic examinations, or organ weight measurements. However, in the highest dose group, macroscopic examination revealed compound-related edema in the mucosa of the nonglandular stomach, which resolved in the recovery group. Microscopic examination indicated acanthosis of the gastric mucosa, inflammatory edema of the submucosa, and several instances of ulcerations in the 1000 mg/kg/day dose group. These effects were attributed to the irritating properties of cocamidopropyl betaine rather than to systemic toxicity. No other treatment-related effects were noted in the organs. Based on the study findings, the NOEL was determined to be 500 mg/kg/day [8].

Genotoxicity

The mutagenic potential of 30.9% and 31.0% active formulations of cocamidopropyl betaine was evaluated through a Salmonella bacterial mutagenicity assay and an L5178Y TK ± mouse lymphoma assay. Cocamidopropyl betaine was nonmutagenic in these assays, indicating the absence of genotoxicity. The genotoxicity studies are summarized in Table 7.

Table 7.

Summary of genotoxicity studies of cocamidopropyl betaine (CAPB)

Assay	Concentration	Results	Refs.
Bacterial Assays using S. typhimurium strains TA98, TA100, TA1535, TA1537, TA1538	0.004, 0.02, 0.1, 0.2, 0.4 μL/plate CAPB (31.0% active)	Negative (with or without metabolic activation)	[28]
Bacterial Assays using S. typhimurium strains TA1535, TA1537, TA1538, TA98, TA100	0.001 and 0.300 μL/plate CAPB (30% active)	Negative (with or without metabolic activation)	[29]
Bacterial Assays using S. typhimurium strains TA98, TA1535, TA1537, TA1538	0, 50, 150, 500, 1500, or 5000 μg/plate CAPB (28.5–30.5% active)	Negative (with or without metabolic activation)	[8]
Bacterial Assays using S. typhimurium strains TA1535, TA1537, TA1538, TA98, TA100	1, 4, 16, 64, 256 μg/plate without S-9 activation and at 4, 16, 64, 256, 1024 μg/plate with S-9 activation	Negative (with or without metabolic activation)	[8]
Mammalian Cell Assays using L5178Y TK ± mouse lymphoma assay	0.001, 0.01, 0.1, 1.0, 10, and 100 μL/mL CAPB (30.9% active)	Negative	[30]
Mouse micronucleus test	0.02 or 0.2 g/kg CAPB intraperitoneal injection	Negative	[9]

S. typhimurium: Salmonella typhimurium

A bacterial assay employing Salmonella typhimurium strains TA98, TA100, TA1535, TA1537, and TA1538 was conducted for cocamidopropyl betaine (31.0% active) at concentrations of 0.004, 0.02, 0.1, 0.2, and 0.4 μL/plate. Cocamidopropyl betaine, irrespective of the presence or absence of metabolic activation, did not induce a significant increase in mutation frequency in any of the tested strains [28].

A bacterial assay of 30% active cocamidopropyl betaine using S. typhimurium strains TA1535, TA1537, TA1538, TA98, and TA100 was conducted with or without metabolic activation [29]. Cocamidopropyl betaine was did not exhibit mutagenicity [29].

An Ames test was performed with 28.5–30.5% active cocamidopropyl betaine using the S. typhimurium strains TA98, TA1535, TA1537, and TA1538, both in the presence or absence of metabolic activation [8]. Cocamidopropyl betaine was not mutagenic [8].

Furthermore, the mutagenicity assays of cocamidopropyl betaine (concentration not stated) were conducted using S. typhimurium strains TA1535, TA1537, TA1538, TA98, and TA100 [8]. Cocamidopropyl betaine exhibited no mutagenic activity, with or without metabolic activation [8].

A mutagenicity study of cocamidopropyl betaine (30.9% active) was performed using L5178Y mouse lymphoma (TK ±), with or without metabolic activation [30]. No significant increase in mutation frequency was observed in any of the treated cultures [30].

In a mouse micronucleus test, OF1 mice (5/sex/group) were administered 0.02 or 0.2 g/kg cocamidopropyl betaine (concentration not stated) by intraperitoneal injection [8]. The doses were given twice at 24-h intervals. No increase in the number of micronucleated PCEs was observed in either dose group compared to the negative control group. Cocamidopropyl betaine was nonmutagenic in mice [8].

Carcinogenicity

An aqueous preparation of a nonoxidative hair dye formulation containing an unspecified grade of cocamidopropyl betaine (0.09% active) was subjected to carcinogenicity testing with groups of 60 male and female random-bred Swiss Webster mice [31]. A dosage of 0.05 mL was applied to the clipped interscapular skin of each mouse three times weekly for 20 months. No adverse effects on average body weight gain, survival, or hematological or urinalysis data were observed in any of the groups. Chronic inflammation of the skin, to varying degrees, was observed in all groups, including the control group. The incidence of neoplasms in the treated animals did not significantly differ from that observed in the control groups [31].

Phototoxicity

A study examined the potential of a 3.0% active aqueous cocamidopropyl betaine solution to induce contact photoallergy in 30 human participants. Of the participants, 11 exhibited mild-to-moderate erythema at the irradiated sites during induction testing. These responses occurred in individuals who had received both UVA and 2 MED of UVB irradiation. These responses were anticipated solely from UVB exposure. Cocamidopropyl betaine did not act as a photosensitizer in this study [18].

Exposure assessment

Systemic exposure doses (SEDs) of cocamidopropyl betaine were calculated via dermal and inhalation exposure routes (Tables 8, 9, 10). Cosmetic products containing cocamidopropyl betaine were surveyed, and the maximum concentration data were obtained from the CIR report [32] or from the maximum concentrations used in China. The estimated daily exposure to a cosmetic product was surveyed with information from the SCCS NoG 2021 [33] and other study reports [34, 35]. According to the CIR report, cocamidopropyl betaine was used at concentrations up to 6% in leave-on products and 11% in rinse-off products [32]. In China, cocamidopropyl betaine was reported to be used at concentrations up to 2.96% in leave-on products and 30% in rinse-off products [36]. Since dermal absorption data are not available, a 50% default value was used for the dermal absorption rate, as noted in SCCS NoG 2021 [33] (Table 8). For products intended for oral use, a conservative absorption value of 100% was used, as noted in SCCS NoG 2021 [33] (Table 9). The calculation of SED was performed with the following equation.

$$\mathrm{SED}=\mathrm{A}\times \mathrm{C}/100\times \mathrm{DA}/100$$

SED (mg/kg bw/day): Systemic exposure dose; A (mg/kg bw/day): Estimated daily exposure to a cosmetic product per kg body weight; C (%): Concentration of cocamidopropyl betaine in the finished cosmetic product; DA (%): Dermal absorption.

Table 8.

Systemic exposure doses (SEDs) of cocamidopropyl betaine for dermal application

Category of product	Product	Maximum concentration (%)	Estimated daily exposure to a cosmetic product (mg/kg/day)	SED (mg/kg/day)
Rinse off skin & hair	Shower gel	30.01)	2.79a)	0.41850
	Shower milk	30.01)	2.79a)	0.41850
	Hand wash soap	30.01)	3.33a)	0.49950
	Hand cleansing liquid soap	30.01)	3.33a)	0.49950
	Solid soap	30.01)	3.33a)	0.49950
	Liquid soap	30.01)	3.33a)	0.49950
	Shampoo	30.01)	1.51b)	0.22650
	Hair conditioner	30.01)	0.67a)	0.10050
	Hair mask	30.01)	0.78b)	0.11700
	Mask	30.01)	0.25c)	0.03750
	Cleansing milk	30.01)	7.34c)	1.10100
	Cleansing gel	30.01)	7.34c)	1.10100
	Exfoliating scrub	30.01)	0.37c)	0.05550
Leave-on skin & hair	Hair oil	9.02)	0.95b)	0.04275
	Hair styling products	9.02)	5.74a)	0.25830
	Styling gel	9.02)	4.64b)	0.20880
	Styling foam	9.02)	20.71b)	0.93195
	Serum	6.03)	11.63c)	0.34890
Facial make-up	Prime face	6.03)	13.52c)	0.40560
Eye make-up	Eyeliner	3.04)	0.08a)	0.00120
	Brow liner	3.04)	0.08c)	0.00120
Make-up remover	Make-up remover	30.01)	8.33a)	1.24950
Deodorant	Nonspray	2.05)	22.08a)	0.22080

¹⁾Concentration reported in China: Rinse-off products

- Concentration reported in FDA VCRP: ²⁾Hair noncoloring, ³⁾Leave-on products, ⁴⁾Eye area, ⁵⁾Deodorant (Underarm)

^a)reference[33]

^b)reference[34]

^c)reference[35]

Table 9.

Systemic exposure doses (SEDs) of cocamidopropyl betaine for oral products

Category of product	Product	Maximum concentration (%)	Estimated daily exposure to a cosmetic product (mg/kg/day)	SED (mg/kg/day)
Oral care product	Toothpaste (adult)	10.01)	2.16a)	0.21600

¹⁾Concentrations reported in FDA VCRP

^a)reference[33]

Table 10.

Systemic exposure doses (SEDs) of cocamidopropyl betaine via the inhalation route

Product	Maximum concentration (%)	Estimated daily exposure to a cosmetic product (mg/kg/day)	SED (mg/kg/day)	SEDinh (mg/kg/day)	SED Total (mg/kg/day)
Deodorant spray (Aerosol)	6.01)	10.00a)	0.25500	0.00234	0.25734
Hair oil (spray)	6.01)	0.95b)	0.02423	0.00022	0.02445
Styling spray (Pump)	6.01)	2.10b)	0.05355	0.00049	0.05404

¹⁾Concentrations reported in FDA VCRP

^a)reference[33]

^b)reference[34]

The assessment of inhalation exposure to cocamidopropyl betaine was performed considering its utilization in spray products (Table 10). The SED for spray products was calculated using the tier II one-box model described in SCCS NoG 2021 [33] with the following equation:

$$\text{SED}=\left[(\mathrm{A}\times \mathrm{C}/100\times f_{\text{evap}}/\mathrm{V}\right]\times \mathrm{IR}\times t$$

SED (mg/kg bw/day): Systemic exposure dose; A (mg/kg bw/day): Estimated daily exposure to a cosmetic product per kg body weight; C (%): Concentration of cocamidopropyl betaine in the finished cosmetic product; f_evap: Evaporating fraction (the worst-case parameter value for SED_inh would be 1); IR (m³/min): Inhalation rate (0.013 m³/min); t (min): Duration of exposure (20 min); V (m³): Volume of the room (size of a standard bathroom: 10 m³)

Safety assessment

The margin of safety (MoS) of cocamidopropyl betaine was calculated based on the systemic effects (Tables 11, 12). The point of departure (POD) was derived from the most relevant study considering the quality and duration of exposure, and the most available POD was subsequently selected for use in the safety evaluation. For systematic POD, a NOAEL of 250 mg/kg bw/day in a repeated-dose oral study for 92 days was used for calculation of the MoS, which is the most conservative value among toxicity studies. Since no more than 50% of the orally administered dose was systemically available, a default oral absorption value of 50% was applied, and the NOAEL was divided by 2. Then, an adjusted NOAEL of 125 mg/kg bw/day was divided by SED for the MoS calculations.

$$\text{Margin of Safety}\left(\text{MoS}\right)=\frac{\text{NO(A)EL}}{\text{SED}}$$

Table 11.

MoS calculations for the products

Product	Maximum conc. (%)	SEDder (mg/kg/day)	SEDinh (mg/kg/day)	SED Total (mg/kg/day)	MoS*
Shower gel	30.0	0.41850	0	0.41850	299
Shower milk	30.0	0.41850	0	0.41850	299
Hand wash soap	30.0	0.49950	0	0.49950	250
Hand cleansing liquid soap	30.0	0.49950	0	0.49950	250
Solid soap	30.0	0.49950	0	0.49950	250
Liquid soap	30.0	0.49950	0	0.49950	250
Shampoo	30.0	0.22650	0	0.22650	552
Hair conditioner	30.0	0.10050	0	0.10050	1244
Hair mask	30.0	0.11700	0	0.11700	1068
Mask	30.0	0.03750	0	0.03750	3333
Clay mask	30.0	0.07650	0	0.07650	1634
Cleansing milk	30.0	1.10100	0	1.10100	114
Cleansing gel	30.0	1.10100	0	1.10100	114
Exfoliating scrub	30.0	0.05550	0	0.05550	2252
Hair oil	9.0	0.04275	0	0.04275	2924
Hair styling products	9.0	0.25830	0	0.25830	484
Styling gel	9.0	0.20880	0	0.20880	599
Styling foam	9.0	0.93195	0	0.93195	134
Serum	6.0	0.34890	0	0.34890	358
Prime face	6.0	0.40560	0	0.40560	308
Eyeliner	3.0	0.00120	0	0.00120	104,167
Brow liner	6.0	0.00120	0	0.00120	104,167
Make-up remover	30.0	1.24950	0	1.24950	100
Deodorant non-spray	2.0	0.22080	0	0.22080	566
Toothpaste (adult)	10.0	0.21600	0	0.21600	579
Hair oil (spray)	6.0	0.0285	0.00148	0.02445	5113
Styling spray (Pump)	6.0	0.0630	0.00328	0.05404	2313
Deodorant spray (Aerosol)	6.0	0.3000	0.01560	0.25734	486

^*Values vary depending on the decimal places of the maximum concentration and SED

Table 12.

MoS calculations for products with inhalation exposure

Example of product	Maximum conc. (%)	SED (mg/kg/day)	SEDinh (mg/kg/day)	SED Total (mg/kg/day)	MoS*
Hair oil (spray)	6.0	0.0285	0.00148	0.02445	5113
Styling spray (Pump)	6.0	0.0630	0.00328	0.05404	2313
Deodorant spray (Aerosol)	6.0	0.3000	0.01560	0.25734	486

^*Values vary depending on the decimal places of the maximum concentration and SED

As shown in Tables 11 and 12, the MoS of the cosmetic products containing cocamidopropyl betaine was greater than 100 at the corresponding concentrations and exposure dosages. Thus, cocamidopropyl betaine is considered safe for the current use.

Funding

This study was supported by the Cosmetic Safety Evaluation Project carried out by the Korea Cosmetic Industry Institute (KCII) funded by the Ministry of Health and Welfare.

Data availability

My manuscript has no associated data.

Declarations

Conflicts of interest

The authors declare that they have no competing interests.