The Safety of Nail Products: Health Threats in the Nail Industry

ABSTRACT

The information on nail product safety is currently limited, but has been increasing in recent years. This increasing research has shown that some ingredients in nail products are hazardous and can lead to both dermatologic and systemic diseases. This risk is present for nail product consumers and is increased for nail technicians. Another concern with the nail products being used is the mislabeling of ingredients. This paper aims to assess the current literature on nail product safety, promote consumer safety, and encourage the involvement of dermatologists in promoting safe nail product use.

1. Introduction

The data on nail product safety is limited, but it has been increasing in recent years. This suggests that some ingredients in nail products may be toxic, leading to dermatologic and systemic diseases. The nail industry is widespread, and nail cosmetics are now used globally by millions of people. By the end of 2031, the nail care industry is expected to be worth 23.1 billion USD [1]. The age of people using cosmetics is getting younger and younger, so the age of people being exposed to potentially harmful chemicals is also getting younger and younger [2]. With this, it is important to promote nail health practices. This starts with understanding the ingredients in nail products, routes of exposure, and their potential hazards. This paper aims to assess the current literature available on this topic and promote consumer safety.

2. Composition of Nail Polish: Toxic Ingredients and Their Potential Effects

Various chemicals in nail polish and nail products can be toxic to humans and have potential adverse effects. One such chemical is phthalates. Phthalates are used in nail polishes and act as a plasticizer [3], commonly used to improve nail polish flexibility and prevent chipping. Dibutyl phthalate (DBP) is a common phthalate used in nail polishes. It was widely used in the early 2000s. However, it was found to be a reproductive and developmental toxin [4]. Toluene is a common solvent in nail products. While toluene itself is not considered to be carcinogenic, it has been shown to cause other adverse health effects [5]. Toxicological and epidemiological studies show that the adverse effects of toluene have been reported as early as the 1950s and were more extensively studied starting in the 1980s [6]. For example, it has been linked to issues with the central nervous, cardiovascular, hematopoietic, reproductive, respiratory, and dermatologic systems [5]. Formaldehyde is present in nail polishes and acts to harden the nail by forming bonds with the naturally occurring keratin in the nails. Formaldehyde has been shown to be carcinogenic and irritating to the respiratory tract [7]. Together, toluene, DBP, and formaldehyde are known as the toxic trio, and there have been efforts to exclude these ingredients from nail products. However, these efforts have been largely unsuccessful [8].

In addition to the toxic trio, other potentially toxic ingredients in nail polishes include Triphenyl phosphate (TPHP). TPHP can be used as a flame retardant or plasticizer and is listed as an ingredient in nail polishes [9]. In fact, between 2012 and 2015, TPHP was the most commonly listed ingredient in half of nail polishes [4]. TPHP is found in nail polish with concentrations ranging from 1% to 14.5% by weight [7]. TPHP can be systemically absorbed, and once absorbed, it is metabolized into diphenyl phosphate (DPHP), which can be excreted in the urine [8]. TPHP has been shown to disrupt thyroid function and reproductive health in humans [4]. Additionally, in a study on zebrafish, it has been shown that TPHP exposure significantly alters neurotransmitters and histamine. It also disrupts hepatic carbohydrate and lipid metabolism [8]. While there have been multiple animal studies demonstrating TPHP risk, human studies have not been extensively conducted.

Methyl methacrylate (MMA) is another potentially hazardous ingredient in nail polish. MMA is a monomer used in nail products that can be inhaled or absorbed via oral or dermal contact. Exposure can lead to issues with the dermatologic, respiratory, reproductive, and neurological systems [10].

Acetone is another harmful ingredient in nail products. It is a highly flammable liquid that is used to remove nail polish. Acetone can be systemically absorbed via inhalation, ingestion, or dermal contact [11]. It is primarily metabolized by the liver into acetol, which is then metabolized to methylglyoxal. Acetol can also be metabolized to L‐1,2‐propanediol, which can be broken down to lactate or acetate. Acetone can irritate mucous membranes and can lead to nausea, vomiting, lightheadedness, headache, restlessness, coma, or respiratory failure, among other effects. It can also lead to kidney and liver damage in severe cases [11].

NMP is a solvent and surfactant used in cosmetics and has been found in nail polish. It can cause irritation of the eyes, nose, throat, and stomach. Additionally, acrylic acid is used as a conditioning agent, binder, and adhesive in nail products. Exposure to acrylic acid can cause irritation of the eyes and respiratory tract [7].

Furthermore, there is a trend of metallic finishes in nail polish that resemble bronze, copper, gold, and silver. These nail polish finishes may contain aluminum, copper, zinc, mica, and bismuth oxychloride. Nail polishes with these finishes have been found to contain significantly higher levels of tin compared to nail polishes without finishes. Additionally, mica can be used as a glitter in different cosmetics and can contain iron, aluminum, magnesium, manganese, or barium itself [12].

Additionally, some pigments used today do knowingly contain metals. For example, manganese violet (ammonium manganese (III) pyrophosphate) and antimony orange (antimony trisulfide). When analyzed, nail polishes have been found to contain concentrations up to 15 μg/g of antimony. However, the antimony guideline is no more than 0.5 μg/g. Antimony is a heavy metal and is commonly used as a pigment [12]. However, antimony is frequently not listed on safety data sheets. Chronic exposure to antimony can cause respiratory irritation, pneumoconiosis, antimony spots on the skin, and GI symptoms. These symptoms typically occur at extremely high concentrations in the air, which is unlikely in a nail salon. However, it is important to note that nail polish guidelines were created for consumers who have much less exposure than nail technicians [12].

N,N‐Dimethyl‐p‐toluidine (DMPT) is another common ingredient in nail products, most commonly in the acrylic liquid monomer component of artificial nail products. It is found in concentrations ranging from 0.1% to 5% by weight and is used to accelerate the polymerization of liquid monomers. It is also found in many nail polish removers and nail polish primers. Animal studies show that DMPT is positively correlated with cancer incidence [7]. In fact, DMPT has been shown to cause cancer of the liver, nose, lungs, forestomach, and thyroid gland in rats [13]. Allergic contact dermatitis, skin sensitization, and burning mouth syndrome have been reported with DMPT exposure as well. Additionally, ingestion of DMPT has been found to cause methemoglobinemia in both animals and children [7].

3. Systemic Health Risks Linked to Nail Polish Ingredients

Nail products can be systemically absorbed via vapor inhalation, dermal absorption through direct skin contact, and unintentional ingestion from nail biting or hand‐to‐mouth behavior [7]. Toluene, DBP, and formaldehyde, also known as the toxic trio, can cause adverse health effects when systemically absorbed [8].

Toluene is a methylbenzene and an aromatic hydrocarbon. It can be absorbed via dermal or inhalation routes. It can slowly be absorbed through dermal exposure into the bloodstream. Toluene also quickly evaporates, making inhalation easier. It has been shown to cause adverse effects in the reproductive and neurological systems [2]. Toluene has also been detected in the breast milk of mothers exposed to nail salons [7].

DBP is a short‐chain phthalate. DBP has high mobility, so when used as a cosmetic on the surface of the skin or nails, there is an easy dermal exposure route through which it can enter the bloodstream. Three peer‐reviewed studies have shown that DBP can cross the skin, and once absorbed, it can cause issues with endocrine and reproductive function [2]. Additionally, while phthalates are not largely associated with allergic contact dermatitis, they can have other systemic adverse effects. Frequent nail polish use is positively correlated with the concentration of phthalate metabolites detected in the urine and serum samples [14]. One health concern associated with phthalate exposure is dysgenesis of the male reproductive system. Some phthalates disrupt germ cell development, and others affect epididymal spermatozoa concentrations. This has been observed in fetal rats. Human data on the risks of phthalates is very limited, although some studies suggest possible effects on the respiratory and immune systems [15].

Formaldehyde is recognized as a carcinogen by both the U.S. National Toxicology Program and the International Agency for Research on Cancer [2]. Typically, it is used in the preservation of biological samples but is also used in a variety of self‐care products, including nail polish. A study found that 58% of nail technicians in and around Salt Lake City, Utah, were exposed to excessive levels of formaldehyde. Formaldehyde has been associated with blood cancer, cognitive disorders, ear, nose, and throat tumors, lung cancer, nervous system injury, and reproductive injury [2].

In addition to the toxic trio, other chemicals found in nail polish have also been found to be potentially hazardous. One toxin that can be ingested via nail products is acetone. Ingestion of acetone can lead to lethargy and confusion, but this occurs with large doses. More serious adverse reactions, however, are seen with acetone‐free nail polish remover. There is a case report of a 15‐month‐old who ingested acetone‐free remover, leading to cardiopulmonary collapse and coma. Another case study of a 9‐month‐old child who ingested acetone‐free remover presented with vomiting, hypotension, bradycardia, respiratory acidosis, and a Glasgow Coma Score of 3. The major chemical in acetone‐free remover is gamma‐butyrolactone. This gets converted to gamma‐hydroxybutyrate (GHB), which is most commonly known for being the date‐rape drug [14].

Additionally, vomiting, cyanosis, lethargy, decreased blood oxygen saturation, increased partial pressure of oxygen, and altered mental status have also occurred with DMPT and nitroethane, both of which are present in some nail polish removers. Both of these compounds can cause cyanosis and methemoglobinemia in children and adults, and this can be potentially deadly [14].

Triphenyl phosphate (TPHP) and its metabolic products have also been detected in human blood samples, breast milk, and umbilical cord blood. TPHP has been shown to be a developmental toxin in both animal and epidemiological studies. In a multigenerational oral exposure study by the National Toxicology Program, exposure to TPHP was associated with delayed puberty in male and female rats. There is also delayed puberty seen in mice exposed to subchronic TPHP concentrations [7]. Additionally, there is an observed reduction in acetylcholinesterase activity in rat pup brains with exposure to TPHP. TPHP has also been shown to cross the blood–brain barrier in zebrafish and mice. Furthermore, epidemiological studies report a positive correlation between concentrations of DPHP (a TPHP metabolite) in pregnant women's urine and the rate of cognitive or behavioral concerns in their children. TPHP exposure alters the liver and metabolism as well. Rats exposed to TPHP demonstrate decreased body weight, increased liver weight, liver cell hypertrophy, and hypercholesterolemia. Additionally, male rats exposed to TPHP showed fatty liver and insulin resistance later in life [7].

TPHP also affects thyroid hormones. A short‐term oral exposure study in rats showed decreased circulating free thyroxine in rats exposed to TPHP. Additionally, hypertrophy of thyroid follicular cells and increased thyroid weight were seen in rats exposed to TPHP. Acetyl tributyl citrate, trimethylpentanediyl dibenzoate, trimethyl pentanyl diisobutyrate, and sucrose acetate isobutyrate can all be alternatives to TPHP use in nail polish. However, the safety of these alternatives has not been sufficiently studied [7].

Acrylic acid is another harmful component in nail products that can be systemically absorbed. In rats, acrylic acid is rapidly absorbed via inhalation and dermal contact. Studies show that acrylic acid inhalation can lead to irritation of the eyes, nose, and skin, as well as damage to nasal and gastric tissues. It can also lead to decreased appetite and body weight. Acrylic acid exposure to the skin can cause severe burns and allergic reactions as well [7].

N‐methylpyrrolidone (NMP) is also used in cosmetics. It is denser than water and has a mild amine odor. It has been found in nail bonders, nail glues, and nail polishes. In the California Department of Toxic Substances Control for Safer Consumer Products (DTSC) studies, NMP was detected in nail polishes targeted toward children that were claiming to be safe and non‐toxic. These nail polishes were found to have concentrations of 1650–39,000 μg/mL [2].

NMP can be systemically absorbed via inhalation, skin contact, or ingestion. Prolonged skin exposure can lead to blistering and dermatitis and increase the absorption of other cosmetic ingredients. Short‐term inhalation exposure can lead to eye, nose, and throat irritation and headaches. Additionally, short‐term effects can be seen from inhalation concentrations as low as 0.7 ppm. Eye exposure can also lead to redness, pain, and blurry vision [2].

Furthermore, studies show that there is no dermal irritation within the first 24 h of dermal exposure. However, in another study, skin irritation was seen in 10 out of 12 workers who were dermally exposed to NMP over 2 days. Animal studies show that dermal, oral, and inhalation exposure to NMP is associated with decreased body weights and increased mortality of fetuses and pups in animals [2].

Additionally, in animal studies, NMP has been found in the mother's milk, and pups that ingest that milk have decreased body weights. Dogs that are orally exposed to NMP show decreased body weights and thrombocytosis. Some other animal studies show that NMP exposure is associated with mild and reversible neurological effects such as lethargy and respiratory irregularities. Skeletal development abnormalities have been reported with NMP exposure as well [2].

Overall, there is a wide range of possible health complications secondary to nail product use. Because this topic lacks sufficient research, more studies need to be done to assess how these complications impact overall human health.

4. Risk of Nail Technicians and Occupational Hazards

Nail technicians are exposed to solvents, acrylics, and plasticizers within the nail care products used. This can lead to maternal complications as well as respiratory and neurological deficits [12]. Compounds, such as acetone, toluene, formaldehyde, and acrylates, are found in nail salons and are considered volatile organic compounds (VOCs), which are lacking regulation in the United States [16].

Worsening of preexisting asthma, new onset asthma, and rhinitis have also been observed in nail technicians [14]. A decrease in mental processing functions has been reported in nail technicians and their children who were exposed in utero to the chemicals in nail products as well. There is also an increased rate of miscarriage in salon workers [17]. In fact, as reported in one study, the miscarriage rate for female nail technicians in California is 15.6% higher than the average reported miscarriage rate for Asian women, who make up the majority of the nail technicians in the United States [16].

Salon workers can be exposed to dust containing harmful materials from nail polish or color powders via inhalation, ingestion through hand‐to‐mouth contact, skin contact, or contaminated water or food. One such material is antimony. An exposure assessment pilot study in 2022 shows that levels of antimony in nail polish exceed cosmetic guidelines [12].

TPHP has also been detected in the air in indoor nail salons. Nail technicians rarely wear gloves and handle nails, nail polish, and nail polish remover with their bare hands. Therefore, they are exposed to TPHP via inhalation and dermal contact [7].

The Occupational Safety and Health Administration (OSHA) recommends wearing long‐sleeved shirts and pants, goggles covering any cut or crack in the skin, hand washing before and after each client and before eating or drinking, applying personal cosmetics, or smoking in order to reduce the risk of dermal exposure. OSHA's recommendation to use personal protective equipment supports the claim that nail salons can be harmful to their employees due to exposure to toxic chemicals [18]. Additionally, OSHA recommends the use of disposable gloves. However, methacrylates are known to penetrate commonly used glove materials [19]. One study found that all non‐sterile gloves, like the ones used in nail salons, are permeable to methacrylates. None of the gloves studied provided protection against skin exposure to MMA. In another study, 2 types of latex gloves were immersed in MMA for 30 min. Both gloves increased in weight, which shows the monomer was absorbed into the latex structure. So, while the glove appears dry, there are still substantial amounts of the monomer within the glove [19]. Therefore, specifically nitrile or neoprene gloves should be used by nail technicians to prevent skin contact and allergen sensitization [14].

Additionally, while OSHA recommends multiple personal protective equipment (PPE) precautions, self‐reported data shows that 55%–75% of nail technicians adhere to PPE recommendations, but observational studies do not support these results [16].

OSHA also recommends using safer products, particularly those with “free” on the label, and using proper room ventilation and fresh air. If a salon is improperly ventilated, a mask or respirator is recommended [18]. Proper ventilation has been shown to decrease asthma symptoms in nail technicians [17].

While dermatologic manifestations are seen in both nail technicians and consumers, more systemic and teratogenic complications are seen primarily in nail technicians, likely due to the duration and frequency of exposure. Market research demonstrates that average consumers apply nail products 2–6 times per month [4], while nail technicians work an average of more than 46 h a week, resulting in more than 40 h of exposure weekly [7].

One way this increased exposure manifests is via inhalation. The inhalation exposure of the toxic chemicals in nail products is dependent on the air concentration and the duration and frequency of exposure. Toluene air concentrations are a product of the toluene content in the products, how much of the product is used, and the ventilation rate within the room [7]. Since the air concentration of these chemicals is higher in a nail salon than at home, nail technicians have higher exposure. Also, because nail technicians spend significantly more time exposed to these chemicals, their exposure is increased compared to standard consumers [7].

5. Mislabeling, Transparency, and Government Regulations

There have been efforts to increase government regulation of cosmetics in an effort to decrease harmful ingredients [14]. In 2004, the European Union (EU) banned DBP use in cosmetics, and in 2006, US companies began voluntarily labeling their nail polish as “3‐Free”. 3‐Free refers to the nail polish not containing the “toxic trio”, which is DBP, toluene, and formaldehyde [4]. However, the California Environmental Protection Agency (CalEPA) studied seven different 3‐Free (toxic trio excluded) nail products. These seven 3‐Free products were found to still contain up to 180,000 ppm of toluene and 82,000 ppm of DBP. These levels far exceed the no‐observed‐adverse‐effect levels (NOAEL) [8]. In another study, 8 out of 10 nail polish samples contained measurable levels of TPHP. Three of the polishes did not list TPHP as an ingredient; however, two of these three did contain TPHP. This study shows that improper ingredient labeling can prevent consumers from avoiding these chemicals [9]. The Environmental Protection Agency found that 83% of products that claimed to be toluene‐free actually contained toluene at concentrations ranging from 190,000 ppm, and 14% of products that claimed to be DBP‐free contained DBP at concentrations up to 88,000 ppm [5]. Furthermore, 5, 7, and 9‐Free nail polishes have also been introduced. 5‐Free is free from DBP, toluene, formaldehyde, formaldehyde resin, and camphor. 7‐Free is free from DBP, toluene, formaldehyde, formaldehyde resin, camphor, ethyl tosylamide, and xylene. 9‐Free is free from DBP, toluene, formaldehyde, formaldehyde resin, camphor, ethyl tosylamide, xylene, parabens, and acetone. While limited data exists on 5, 7, and 9‐Free nail polishes, the existing data also indicates mislabeling with these products [2].

The US Food and Drug Administration (FDA) also implemented the Federal Food, Drug, and Cosmetic Act. The European Union Commission implemented Cosmetics Regulation No. 1223/2009. The European regulations require the manufacturers and distributors of cosmetic products to provide consumers with the ingredients and safety information. They regulate the adequate labeling of products and restrict the use of harmful chemicals [14]. They also require the warning statements for products with potentially harmful ingredients that have not yet been studied. The cosmetic regulation No. 1223/2009 also created a cosmetovigilance in which a communication network was established to report undesirable effects of cosmetics. This requires the severity of these effects to be analyzed and reported to the distributors and the government authorities. The European Community Cosmetics Directive was passed in 2004 and required all of the ingredients in a cosmetic product to be listed on the product [14]. The European Union (EU) has also banned the intentional use of antimony, arsenic, cadmium, nickel, chromium, cobalt, mercury, and lead in cosmetics due to their neurological and reproductive toxicity. The United States has not done this [12].

The FDA has, however, established the Cosmetic Ingredient Review Expert Panel. This is an industry‐funded panel of experts that analyzes cosmetics for ingredient safety. However, this poses a conflict of interest when the people profiting off the sale of the products are also the ones analyzing the products for safety [14].

The United States and European law have attempted to restrict the use of certain allergens in cosmetics. While steps have been taken to restrict allergens based on the literature, the literature regarding nail products is significantly lacking. While other cosmetics have reduced allergens, very few measures have been made to decrease allergens in nail products. Furthermore, toluenesulfonamide‐formaldehyde resin (TSFR) is one of the most studied allergens associated with nail polish. However, the FDA has not banned this component. They instead recommend caution and careful label reading before purchasing formaldehyde‐containing cosmetics [14].

In 2015, Europe's Scientific Committee on Consumer Safety reduced the maximum level of formaldehyde in nail hardeners from 5% to 2.2%. This was thought to reduce sensitization and allergy to formaldehyde‐containing resins while still allowing for the hardening and sensitization these compounds provide. Europe has also limited the use of phthalate plasticizers due to the possible carcinogenicity and birth defects that have been shown in animal studies. The FDA, however, has not restricted phthalate use due to the lack of definitive evidence in human studies [14].

Additionally, while the FDA does regulate cosmetics, it does not require premarket safety testing. The FDA requires proof that an ingredient harms human health in order for it to be restricted. Therefore, since 1939, fewer than 12 ingredients have been prohibited or restricted [4]. One example of a restriction is the use of MMA. The use of MMA was originally widespread, but it was restricted in the US and Europe due to causing severe contact dermatitis. Products with 100% MMA monomer may no longer be used in the US, and products with > 90% MMA were recalled in Europe. While this is a step in the right direction, this regulation still allows MMA to be used [14].

Furthermore, OSHA does require safety data sheets to be available to workers in nail salons, but these only have to disclose ingredients that have been tested and proven to be hazardous beyond a certain concentration [4].

While some nail polish labels have added statements reporting their exclusion of certain toxic chemicals, these are not always accurate [12]. In fact, labeling and advertising a nail product as 3‐Free also do not need premarket approval by the FDA. The FDA does require ingredient labels on nail polishes sold to consumers, but they do not require them on products for salon use only. Additionally, phthalates can be listed as “fragrance”. Also, disclosure requirements do not extend to incidental ingredients. Incidental ingredients are described as ingredients that are components of another ingredient and have no functional effect on the end product [4].

6. Consumer Advocacy and a Call for Stricter Regulations

Overall, there is limited data on the long‐term health concerns associated with nail products. Therefore, first and foremost, there needs to be more research into the ingredients and their possible hazards so the regulating bodies can implement more extensive and accurate guidelines. Additionally, this will help the public and nail salon employees to be able to make informed decisions about product consumption. Because the research into nail product safety is relatively limited, there is little research examining the safety of alternatives. As more research is done, this will hopefully lead to the development of safer alternatives.

Additionally, increasing knowledge of the toxic chemicals to both salon workers and consumers is essential to improving purchasing decisions. The current mislabeling of products as being free of hazardous ingredients is leading to consumers unknowingly being exposed to these toxins when they think they are protecting themselves. Proper labeling of nail products needs to be regulated to allow consumers to make informed decisions regarding their own health [8].

Furthermore, a policy to regulate and promote safe practices in nail salons could help prevent further harmful exposure. Stricter enforcement of OSHA guidelines in nail salons, along with proper labeling of nail products and adequate ventilation, can help protect both nail technicians and consumers from harmful toxins [16]. FDA guidelines should also require proper testing and accurate labeling of nail product ingredients.

Because dermatologists treat diseases of the nail, they should be well educated on nail health and promote healthy nail practices. They need to be aware of the possible risks associated with the use of nail products and be able to counsel patients accordingly. Dermatologists should not necessarily advise against using nail products, but they should be able to inform their patients of possible risks associated with them. They should also be able to know which nail diseases could be caused by nail products and recognize when this is the case. Discontinuing a nail product could be a much simpler remedy for some diseases of the nail, so recognizing when this is an option can improve patient care.

Additionally, as dermatologists treat skin cancer, they are responsible for advising their patients on the risks of sun exposure and promoting UV protection. The same could possibly be applied to nail products in the future. If these products do cause dermatologic or systemic diseases, then dermatologists will need to be able to counsel patients on this. Compared to skin cancer data, nail product data is far more primitive and insufficient at this time. Therefore, much more research needs to be done on the topic. Dermatologists will need to understand this data and share it with patients to promote healthy practices and informed decision‐making.

7. Conclusion

In conclusion, many ingredients in nail products have been shown to be potentially hazardous to human health. These effects range from dermatologic manifestations to various cancers and reproductive and neurological deficits. With the growing evidence suggesting this, more regulation should be needed to promote consumer safety when using the products. Overall, much more research is required in order to come to a conclusion on the risk assessment of nail products, but the current data show that there needs to be more consistent and accurate labeling and a better understanding of the possible risks.

Conflicts of Interest

The authors declare no conflicts of interest.