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.