Keratosis pilaris (KP) (also follicular keratosis, lichen pilaris, or colloquially “chicken skin”) is a common, autosomal dominant, genetic condition of the skin’s hair follicles characterized by the appearance of possibly itchy, small, gooseflesh-like bumps, with varying degrees of reddening or inflammation. It most often appears on the outer sides of the upper arms, (the forearms can also be affected), thighs, face, back, and buttocks; KP can also occur on the hands, and tops of legs, sides, or any body part except glabrous (hairless) skin (like the palms or soles of feet). Often the lesions can appear on the face, which may be mistaken for acne.
There are several types of keratosis pilaris and it has been associated with pregnancy, type 1 diabetes mellitus, obesity, dry skin, allergic diseases (e.g., atopic dermatitis), and rarely cancer. Many rarer types of the disorder are part of inherited genetic syndromes.
The cause of keratosis pilaris is incompletely understood. As of 2018, keratosis pilaris is thought to be due to abnormalities in the process of depositing the protein keratin in hair follicles, abnormalities in the hair shaft, or both. Keratosis pilaris is usually diagnosed by a medical professional based on the appearance of the skin but dermoscopy can be used as well if the diagnosis is unclear.
Keratosis pilaris is the most common disorder of the hair follicle in children. It is unclear how common KP is in adults with estimates ranging from 0.75% to 34% of the population. No single approach has been found to completely cure keratosis pilaris but treatments can improve the cosmetic appearance of the condition. Treatment includes the application of topical preparations of moisturizers and medications such as lactic acid, salicylic acid, urea, or retinoids to the skin. Fractional carbon dioxide lasers and Nd:YAG laser therapies are also effective.
Signs and symptoms
Keratosis pilaris results in small, rough bumps on the surface of the skin. They are skin-colored bumps the size of a grain of sand, many of which are surrounded by a slight pink color in light skinned people and dark spots in dark skinned people. Most people with keratosis pilaris do not have symptoms but the bumps in the skin can occasionally be itchy. Irritation due to scratching KP bumps can result in redness and inflammation.
Though people with keratosis pilaris experience the condition year-round, the problem can become exacerbated and the bumps are likely to look and feel more pronounced in color and texture during the colder months when moisture levels in the air are lower. The symptoms may also worsen during pregnancy or after childbirth. It is speculated that increased sun exposure can mitigate the symptoms of KP.
Keratosis pilaris occurs when the human body produces excess amounts of the skin protein keratin, resulting in the formation of small, raised bumps in the skin often with surrounding redness. The excess keratin, which is the same color of the person’s natural skin tone, surrounds and entraps the hair follicles in the pore. This causes the formation of hard plugs (process known as hyperkeratinization). Many KP bumps contain an ingrown hair that has coiled. This is a result of the keratinized skin’s “capping off” the hair follicle, preventing the hair from exiting. The hair grows encapsulated inside the follicle. KP is more common in patients affected by atopic diseases such as allergic rhinitis and atopic dermatitis.
Keratosis pilaris subtypes are occasionally part of genetically inherited syndromes associated with intellectual disability, neuro-cardio-facial-cutaneous syndromes, RASopathies, ectodermal dysplasias, and certain myopathies.
Physicians can often diagnose keratosis pilaris simply by examining the skin; tests are usually not needed. However, a dermatologist can use dermoscopy to confirm the diagnosis and assess if a person with KP is responding to treatment. Physicians will often consider family history and the presence of symptoms when making the diagnosis. Those with this condition are generally encouraged to contact a physician if the bumps are bothersome and do not improve with over the counter lotions.
Several medications can cause a skin eruption similar to keratosis pilaris. Medications known to produce this type of skin eruption include cyclosporine, BRAF inhibitors, and tyrosine kinase inhibitors.
There are several different types of keratosis pilaris. Variations of keratosis pilaris include keratosis pilaris rubra (red, inflamed bumps which can be on arms, head, legs), keratosis pilaris alba (rough, bumpy skin with no irritation), keratosis pilaris rubra faceii (reddish rash on the cheeks), keratosis pilaris atrophicans, keratosis follicularis spinulosa decalvans, atrophoderma vermiculatum, keratosis pilaris atrophicans faciei, erythromelanosis follicularis faciei et colli, and papular profuse precocious keratosis pilaris.
Keratosis pilaris is commonly described in association with other dry skin conditions, such as ichthyosis vulgaris, dry skin and atopic dermatitis, including those of asthma and allergies.
Keratosis pilaris does not bear any known, long-term health implications, nor is it associated with increased mortality or morbidity. It is not related to goose bumps, which results from muscle contractions, except that both occur in the area where the hair shaft exits the skin.
Keratosis pilaris is medically harmless, but many individuals may seek treatment as the condition can cause emotional distress. Topical creams and lotions are currently the most commonly used treatment for keratosis pilaris, specifically those consisting of moisturizing or keratolytic treatments, including urea, lactic acid, glycolic acid, salicylic acid, vitamin D, or topical retinoids such as tretinoin. Improvement of the skin often takes months and the bumps are likely to return. Limiting time in the shower and using gentle exfoliation to unplug pores can help. Many products are available that apply abrasive materials to and alpha or beta hydroxy acids to assist with exfoliation.
Some cases of keratosis pilaris have been successfully treated with laser therapy, which involves passing intense bursts of light into targeted areas of the skin. Depending on the body’s response to the treatment, multiple sessions over the course of a few months may be necessary.
Worldwide, KP affects an estimated 30-50% of the adult population and approximately 50-80% of all adolescents. It is more common in women than in men, and is often present in otherwise healthy individuals. The skin condition is prevalent in persons of all ethnicities. No particular ethnicity is at higher risk for developing keratosis pilaris. Although keratosis pilaris may manifest in persons of any age, it usually appears within the first decade of life and is more common in young children. In most cases, the condition gradually improves before age 30, however it can persist longer.