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 or folliculitis.
The several types of KP have 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 KP is not completely understood. As of 2018, KP 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. KP 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. Variants of the ABCA12 gene have been associated with KP.
KP is the most common disorder of the hair follicle in children. How common it is in adults is unclear since keratosis pilaris is an underreported condition and the actual prevalence of the condition may be higher than estimated. No single approach has been found to completely cure KP, but treatments can improve the cosmetic appearance of the condition. Treatment includes the application of topical preparations of moisturizers and medications such as glycolic acid, 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
KP 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 KP 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 KP experience the condition year-round, the problem can become exacerbated, with the bumps 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. Increased sun exposure might mitigate the symptoms of KP.
Pathophysiology
KP 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 as the person's natural skin tone, surrounds and entraps the hair follicles in the pore. This causes the formation of hard plugs (a 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.
KP subtypes are occasionally part of genetically inherited syndromes associated with intellectual disability, neuro-cardio-facial-cutaneous syndromes, RASopathies, ectodermal dysplasias, and certain myopathies.
Diagnosis
Physicians can often diagnose KP simply by examining the skin without specialized tests, but a dermatologist can use dermoscopy to confirm the diagnosis and assess if a person with KP is responding to treatment. Physicians 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.
Differential diagnosis
Several medications that can cause a skin eruption similar to KP include cyclosporine, BRAF inhibitors, and tyrosine kinase inhibitors.