Keratosis Pilaris Unveiled: Insights into its Origin, Management Strategies and Research Frontiers

Abstract

Follicular hyperkeratosis is frequently known as keratosis pilaris (KP). Small, folliculocentric keratotic papules with possible erythematous borders are its defining features. It is a common, asymptomatic skin disorder. The tiny papules give the skin a stippled, gooseflesh-like appearance. The disorder most frequently affects the exterior portions of the upper arms, upper legs and buttocks. It is caused by prolonged exposure to the sun and people suffering from dry skin. The consequences of KP disease are mainly triggered by dryness and rough skin, which results in bumpy skin, redness, irritation, itching and hyperpigmentation. It can affect persons of any age, but it is more prevalent in children and teenagers. While the classic KP is known, the other variants are also there which have particular effects on the different parts of the body. To alleviate symptoms, apply moisturizers, exfoliates and topical treatments containing urea, lactic acid or salicylic acid. This critical issue must be addressed; there have been very few clinical studies, and this study will assist researchers in carrying out more clinical trials and studies on KP disorder. Being aware of KP is a very important point while it is not entirely preventable, using regular moisturizer, keeping gentle exfoliation and the use of light cleansers can all help to manage and reduce its appearance. There are a few current therapies used to treat the disease, including laser and blue light treatments, and photodynamic therapies.

Introduction

‘Keratosis pilaris’ (KP) is a common mild skin ailment that usually affects adolescents and adults. It is also known as follicular hyperkeratosis.[1] It can be stressful for the psychological and social surroundings due to its apparent appearance. KP commonly worsens during puberty. The sites of predisposition are the upper arms (92%) and thighs (59%), muscle areas, as well as the buttocks (30%).[2] Many patients with this genetic disorder of hair follicle keratinization have a family history. The majority of patients are thought to have problems with the keratinization process, and keratin buildup is thought to be the primary cause of the disease.[3] Individual papules develop as a result of an accumulation of extra skin cells and debris close to the hair follicles, which prevent the hair follicles from reaching the surface. Under the papule, coils of hair are frequently visible.[4] A genetic skin condition called ichthyosis vulgaris causes dead skin cells to build up on the surface of the skin as thick, flaky scales.[5] The presence of KP on the upper limbs was associated with lower prevalence and lower severity of acne, which is a skin condition that leaves spots after pimples occur and is increasingly common today.[6]

Although the classic form of KP is well-known, various variants of this condition exist, each with distinct characteristics. The different variants of KP include ‘Keratosis pilaris rubra’, ‘Keratosis pilaris alba’, ‘Keratosis pilaris atrophican’, ‘Keratosis follicularis spinulosa decalvans’, ‘Erythromelanosis follicularis faciei et colli’ and ‘Keratosis pilaris lichenoides’.[7] For managing the KP symptoms, patients use emollients, exfoliants, anti-inflammatory medications, sun protection products and humidifiers. Dermabrasion, photodynamic therapy, laser treatment and blue light treatment are examples of current, sophisticated therapies for treating KP condition.[8] All prospective scholars and dermatological researchers will benefit from the thorough analysis and research provided by this comprehensive review, which will also include a full data collection for future reference.

Aetiology and Pathophysiology of KP

KP, especially its rubra variation (KPR), is caused by ‘hyperkeratinization’ of the hair follicles. Keratin, a skin-protective protein, accumulates and forms plugs in hair follicles, resulting in the formation of KP’s characteristic tiny bumps.[9] The surrounding redness in KPR is caused by dilated superficial blood vessels and inflammation, distinguishing it from the more frequent KP alba, in which the bumps are skin-coloured or whitish and lack erythema.[10] As of 2018, it is believed that KP is brought on by abnormalities in the hair shaft, or abnormalities in the hair follicles during the deposition of the protein keratin, or both.[11] Excess keratin in the follicular orifices produces sticky plugs that enlarge the follicle’s infundibulum, resulting in the papules of KP.[12] There is visible superficial, mild vascular redlining penetration in the upper dermis and per-follicular regions. The epidermis exhibits mild hyperkeratosis, hypergranulosis and follicular clogging.[13] Although the parakeratotic cells are not preserved within the follicle, the stratum corneum may show localized parakeratosis.[14] The sebaceous glands, arrectores pilorum and keratotic plug may atrophy as a result of the keratotic plug’s deep penetration into the hair follicle. The plug, in particular, is made up of horny lamellae and frequently captures one or more coiled, brittle hairs, as shown in Figure 1.[15]

Figure 1.

Pathophysiology of keratosis pilaris

Variants of KP

KP has multiple variations, each with distinct features, even though the classic variety is the most commonly recognized.[7] Various forms of KP are examined in depth below:

• Keratosis Pilaris Rubra (KPR): This type can be identified by prominent erythema (redness) in addition to the characteristic rough bumps.[16] Increased blood flow in the area is the cause of the redness. Affected areas have a characteristic rough, bumpy texture and considerable redness, generally in the cheeks, upper arms, or thighs.[17] The bumps may stand out more on the red background. Most often seen on the face, especially the cheeks, but it can also impact other body areas like the thighs and upper arms.[18]

• Keratosis Pilaris Alba (KPA): This is the classic and most prevalent type of KP, with hard, tiny, white pimples that resemble sandpaper. In most cases, these lumps are not inflammatory, often observed on the thighs, buttocks, upper arms and occasionally on the face.[19]

• Keratosis Pilaris Atrophicans: Along with the usual KP pimples, this rare and more severe variation also exhibits scarring and atrophy (thinning of the skin). There are patches of thinned skin and scarring, as well as rough lumps and it frequently affects the neck, face and even the scalp.[20]

• Erythromelanosis Follicularis Faciei et Colli (EFFC): A variation that manifests as redness, follicular plugging (bumps) on the face and neck and hyperpigmentation. Follicular keratosis causes red to brown spots with a rough texture that primarily affects the cheekbones, jawline and neck.[21]

• Keratosis Pilaris Lichenoides: It is a less common type with KP symptoms along with lichenoid (lichen planus-like) alterations. Similar to typical KP, but with more inflammatory flat-topped reddish-brown papules, these bumps can afflict the arms, legs and trunk among other portions of the body.[22]

Factors contributing to the progression of the disease

• Overabundance of a hard protein (Keratin): In some body locations, this combines with dead skin cells to produce a clog that obstructs the hair follicle. Keratin inhibits hair follicles from opening, creating rough, bumpy skin areas. It may arise from hereditary illnesses or skin problems such as atopic dermatitis.[23]

• Genetic predisposition: There is a hereditary component to KPR because it frequently runs in families. The underlying genes are unknown; however, it is thought to be inherited in an autosomal dominant pattern.[24]

• Skin type and environment: Individuals with dry skin or atopic dermatitis (eczema) are more vulnerable to KP and its related diseases. Fair-skinned people are more likely to experience KPR, which is frequently made worse by cold, dry weather.[25]

• Age: KPR usually begins in childhood and can last into adolescence and adulthood; however, it commonly improves with maturity.[26]

• Hormonal factors: Some individuals suffer an exacerbation of symptoms with hormonal changes, such as puberty or pregnancy.[26]

Symptoms of KP

KP can be identified by several apparent signs, the most prominent of which concern the appearance and texture of the skin.[27] Following are the main signs associated with KP [Figure 2].

Figure 2.

Symptoms of keratosis pilaris

• Small and rough bumps: These bumps are typically flesh-coloured, white, red, or brown. They have a rough texture and feel similar to sandpaper.[28] The bumps may vary in colour, frequently matching the skin tone, although they can also seem reddish, especially if agitated.[28]

• Redness and inflammation: Some people may feel mild redness around the bumps, particularly if their skin becomes inflamed. This inflammation can make the region appear more visible, particularly in persons with pale skin.[29]

• Itching and irritation: In specific conditions, the skin around the bumps may turn red and inflammatory, particularly if it has been scraped or irritated, and the affected regions may feel dry and itchy.[30]

• Skin discolouration: Some people may notice mild skin darkening around the lumps, which is particularly noticeable in darker skin tones. The discolouration may present as moderate hyperpigmentation surrounding the pimples.[15]

• Seasonal variation: The disease may worsen during the winter months because of the dry air. On the other hand, during the summer, when humidity is higher and skin tends to retain moisture better, many people report that their symptoms have improved.[31]

Additional factors initiating KP

The additional initiators of the disease are hair removal methods, friction, dry weather and dry skin conditions, which are detailed in Table 1.

Table 1.

Keratosis pilaris initiating factors

Factors	Description	Reference no.
Hair removal methods	• Shaving and waxing are common hair removal techniques that cause keratosis pilaris on the arms and legs.	[32,33]
	• These procedures put your skin under mechanical stress, which can exacerbate the condition and cause more lumps, irritation and redness on the skin.
Friction	In addition to hair removal techniques, friction from rough objects and constricting clothing can exacerbate this problem.	[34]
Dry weather	• In cold, dry weather, keratosis pilaris is known to get worse. Your skin finds it difficult to stay moisturized when the air is dry.	[15,31]
	• This explains why your skin tends to peel, flake, or crack more during the winter. A buildup of dead skin cells increases your risk of hair follicle congestion, which can result in keratosis pilaris.
Dry skin conditions	People with dry skin are more prone to keratosis pilaris, though the exact cause of the trigger for hyperkeratinization is still unknown.	[23]
	Keratosis pilaris can become worse if xerosis, eczema, or ichthyosis vulgaris already exist.

Management and Modern Treatments of KP

KP is a metastatic disorder in which a person improves over time. However, patients can have rapid healing of skin lesions by maintaining good hygiene, using hypoallergenic soaps and avoiding touching the papules.[27] Among the treatments applied topically are emollients and topical keratolytic agents. KP typically improves with age, though some patients may notice worsening symptoms over time.[35] Symptoms can be lessened but there is no permanent cure for the condition. Several options for controlling KP include reducing symptoms and improving skin appearance.

The treatment aims to moisturize the skin, reduce keratin accumulation and manage inflammation. Various treatment options available for this problem are as follows:

1. Moisturizing creams and lotions:

   • Emollients: Regular use of moisturizing lotions and creams softens the skin and reduces the appearance of KP.[35] Look for products that contain urea, lactic acid, or glycerine, as these ingredients assist to moisturize and eliminate dead skin cells.[36]

   • Lanolin and petrolatum-based products: These components can preserve moisture and shield the epidermal barrier.[37]

2. Exfoliating treatments:

   • Alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs): To help exfoliate the skin and smooth out any bumps, creams or lotions with glycolic, lactic, or salicylic acids can be used. Additionally, the keratin plug’s thickness may be reduced with the aid of these acids.[38]

   • Mechanical exfoliation: Dead skin cells can be removed with mild washing with a loofah or soft brush, but caution must be used to prevent skin irritation or damage.[39]

3. Topical retinoid:

   • Tretinoin: They can aid in promoting cell turnover and preventing hair follicle clogging. They are produced from vitamin A.[15] Adapalene (Differin), an over-the-counter retinoid medication, can be useful; alternatively, a dermatologist may suggest prescription-strength alternatives. Use them as directed as they may cause sensitivity or irritation.[40]

4. Other preventive measures:

   • Humidifiers: Preventing excessive dryness of the skin, which could worsen KP, can be achieved by keeping the air in your house moist, particularly in the winter season.[41]

   • Sun protection: Using sunscreen helps shield the skin from further rashes and hyperpigmentation.[25]

   • Prescription creams: Low-strength corticosteroid creams may be recommended in some situations to lessen redness and irritation.[42] However, because long-term use may have adverse effects, these are typically only meant to be used temporarily.[2]

To treat KP some advanced modern therapies [Figure 3] are as follows:

Figure 3.

Modern therapies of KP

1. Dermabrasion: A cosmetic procedure that uses a rotating tool or wire brush to remove the skin’s outermost layers.[43] Usually, a dermatologist or plastic surgeon does it to address different skin issues. The process aids in the development of new, smoother skin, giving a more even and polished appearance.[44] The uses and indications for dermabrasion therapy are mentioned in Table 2.

2. Photodynamic treatment: A medical procedure that uses a certain wavelength of light in combination with a photosensitizing agent.[47] This substance reacts to light to target and kill aberrant cells. Actinic keratosis, acne and some forms of cancer are among the ailments that it is frequently used to treat.[48] The benefits of photodynamic treatment are mentioned in Table 3.

3. Laser treatment: KP can be treated with lasers by focusing on the underlying causes of the condition, such as inflammation, excess keratin build-up and inconsistencies in skin texture.[51] The benefits of laser treatment are mentioned in Table 4.

   • Types of laser treatments for KP:

   • Pulsed dye laser (PDL): This kind of laser reduces KP-related redness and inflammation by focusing on the skin’s blood vessels. The device uses a concentrated beam of yellow light to treat abnormal blood vessels in the skin. PDL may be useful for people whose redness is excessive in addition to their pimples.[52]

   • Fractional laser (e.g., Fraxel): KP bumps are less noticeable and skin texture is improved by this laser treatment. It functions by inflicting microscopic wounds on the skin, which stimulate the production of new collagen and skin cells by the body and results in smoother skin.[53]

   • Nd laser: This type of laser is sometimes utilized for more extensive cases because it may penetrate the skin deeper. It facilitates smoother skin by lowering redness and inflammation.[54]

4. Blue light treatment: It targets the skin by applying particular light wavelengths, usually about 415 nm.[57] This light has the ability to reach the higher layers of the skin and has been demonstrated to eradicate acne-causing bacteria, specifically Propionibacterium acnes. It can also help to lessen redness and swelling because of its anti-inflammatory properties.[57] The benefits of blue light treatment are mentioned in Table 5.

Table 2.

Uses and indications for dermabrasion therapy

Skin issues	Uses and indications	Reference no.
Scars	It is especially efficient at reducing the look of acne scars, surgical scars and injury scars.	[45]
Fine lines and wrinkles	It can help with fine wrinkles around the mouth and general skin texture.	[46]
Sun damage	Helps to reduce the effects of sun exposure, such as uneven skin tone and pigmentation issues.	[25]

Table 3.

Benefits of photodynamic treatment (PDT)

	Benefits of PDT	Ref.
Targeting keratin production	KP is characterized by the accumulation of keratin in hair follicles; PDT could theoretically aid to restore keratin production and minimize the accumulation.	[48]
Anti-inflammatory effects	PDT offers anti-inflammatory qualities, which may help to lessen the redness and inflammation that sometimes accompany KP.	[49]
Reducing hyperkeratosis	By focusing on the cells that produce keratin, PDT may be able to reduce the excessive keratin accumulation that causes the distinctive KP bumps	[50]

Table 4.

Benefits of laser treatments

	Benefits of laser treatments	Ref.
Targeting redness and inflammation	Laser treatments, particularly pulsed dye laser, can considerably lessen the redness commonly associated with KP. These lasers produce a specific wavelength of light, which is absorbed by haemoglobin in blood arteries. This absorption produces heat, forcing blood vessels to coagulate and shrink, thus reducing redness and inflammation in the treated area.	[55]
Reducing keratin build-up	Some lasers can also assist minimize keratin build-up by enhancing general skin health and aiding the removal of dead skin cells. This can keep keratin from blocking the hair follicles, which is an important element in KP.	[56]
Penetrating deeper skin layers	Nd lasers can penetrate deeper into the skin, focusing on both the upper and deeper dermal layers. This enables more extensive treatment, particularly for people with severe KP, deeper pigmentation, or skin texture problems.	[3]
Smoothing skin texture	Fractional lasers, such as the Fraxel laser, are used to address this by inducing micro-injuries in the skin. As damaged skin cells are replaced by new, healthy ones, the skin texture becomes smoother and more even. The fractional method treats only a piece of the skin at a time, allowing for faster healing and a lower chance of problems.	[53]

Table 5.

Benefits of blue light treatment

Benefits of blue light treatment		Reference no.
Reduction of inflammation	Due to its anti-inflammatory qualities, blue light may help lessen the redness and swelling caused by KP. Given that certain KP patients have inflammation around their hair follicles, blue light can reduce this reaction and relieve redness and irritation on the skin.	[58]
Improvement in skin texture	Blue light mostly targets germs, but because it also reduces inflammation, it can occasionally enhance the texture of the skin, gradually lessening the prominence of KP bumps.	[53]
Complementary treatment	In addition to other treatments like topical exfoliates (such as glycolic acid and salicylic acid) or emollients, blue light therapy may be used. It might improve the efficacy of other medicines by lowering inflammation.	[58]

Investigator Global Assessment score

A standardized scoring method called the Investigator Global Assessment (IGA) is used to determine the severity of skin disorders like KP.[59] This grading system assists dermatologists and other medical professionals in determining the severity of the problem accurately and consistently, tracking changes over time and assessing the effectiveness of various therapies.[60] The usual range of the IGA score for keratosis pilaris is 0 to 4, with each grade denoting a different severity level as illustrated in Figure 4. Table 6 describes the KP IGA score with further details.[59]

Figure 4.

Investigator Global Assessment score ranges

Table 6.

The IGA score ranges and severity level of KP

IGA ranges	Severity level	Description	Touch	Reference No.
IGA 0	Clear	No rough patches, bumps, redness and inflammation.	Skin feels smooth with no palpable roughness or bumpiness.	[61]
IGA 1	Almost clear	Minor and few rough patches and bumps.	Slightly rough texture with barely bumps on the skin but it is not prominent.	[7]
IGA 2	Mild	Small, noticeable bumps, redness and slight rough patches.	Skin feels slightly rough with palpable bumps but they are not significantly raised.	[62]
IGA 3	Moderate	Clear and noticeable bumps, rough texture and moderate redness.	Skin feels rougher, with multiple raised, palpable bumps. The texture changes are prominent and noticeable to touch.	[62]
IGA 4	Severe	Large, raised bumps, severe roughness, marked redness and inflammation.	Skin feels very much rough, with numerous and larger palpable bumps. The roughness is severe and easily detectable by touch.	[62]

Clinical Studies on KP

Some clinical studies particularly regarding the disorder KP are mentioned in Table 7.

Table 7.

Clinical trials for keratosis pilaris

Clinical trial ID	Title	Phase	Start/end date	Type of formulation	Intervention	Summary
NCT05535517 (Recruiting)	‘Development and validation of an Investigator Global Assessment score for Keratosis Pilaris’	NA	August 2022 to August 2023	CeraVe Salicylic Acid (SA) Smoothing Cream	Device: M22 IPL	By evaluating the composite IGA score on patients and comparing it to a standard 0–4 IGA that will be developed specifically for KP.
NCT01281644 (Completed)	‘Treatment of Keratosis Pilaris with 810 nm Diode Laser (KP)’	NA	March 2011 to October 2011	-	Device: Diode laser	The difference in blind rater severity scores between the treated and untreated sites is the primary outcome of interest. The optional result of revenue is the adjustment of the patient’s self-evaluated severity score of the treated site.
NCT04797663 (Completed)	‘Long-pulsed 1064 nm Nd-YAG laser versus TCA 20% in treatment of Keratosis pilaris’	NA	March 2021 to July 2021	TCA 20%	Device: Nd: YAG laser Drug: TCA 20%	Keratosis pilaris treatment options include the Nd: YAG laser and chemical peels, although the research does not provide enough support for their effectiveness. In order to treat KP, this study compares and evaluates the effectiveness of trichloroacetic acid 20% and long-pulsed Nd: YAG laser therapy.
NCT03243617 (Completed)	‘Cosmetic Study of AO+ Mist in improving the appearance of skin afflicted with Keratosis pilaris’	4	May 2013 to September 2015	NA	Other: Placebo Other: AO+ Mist	This study aims to show the efficacy, safety and tolerability of AO+ Mist when used daily for 4 weeks to enhance the appearance of skin with KP.

1. ‘Development and validation of an Investigator Global Assessment score for Keratosis pilaris’[59]

2. ‘Treatment of Keratosis pilaris with 810 nm Diode Laser (KP)’[62]

3. ‘Long-pulsed 1064 nm Nd-YAG laser versus TCA 20% in treatment of Keratosis pilaris’[63]

4. ‘Cosmetic study of AO+ Mist in improving the appearance of skin afflicted with Keratosis Pilaris’[64]

Although they may result in a modest improvement, topical retinoids, calcipotriol and keratolytic ointments are not highly effective, according to the literature. Although extended therapy is necessary, many authors have reported positive responses to acitretin and etretinate.[65]

Conclusion and Future Directions

KP is a common yet innocuous skin condition that can cause significant distress to the patient because of its rough texture, dryness and appearance. There are various options to manage its symptoms, and the main aim of treatment is to reduce abnormal folliculocentric thickness, dryness, redness and inflammation. Some advanced modern therapies are introduced for treating KP, which include dermabrasion, photodynamic therapy, laser treatments and blue light treatment. To develop more specialized therapy techniques or preventive strategies, future studies should focus on the genetic foundation of the illness. Increasing public knowledge of this illness can also assist patients in receiving the right care and lessen any potential psychological effects. The outlook and prospects for KP and its variants rely upon expanding our awareness of the disorder and enhancing the possibilities for treatment, which may include combination therapy, innovative topical medications and genetic investigations. Large-scale clinical trials to assess the efficacy of new and existing treatments, including both topical and systemic options, will be crucial for developing evidence-based guidelines. The future prospects for KP are promising, with ongoing research likely to yield more effective and personalized treatments that can better manage symptoms and improve the quality of life of patients.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.