Keratosis pilaris results from the buildup of keratin — a hard protein that protects your skin from harmful substances and infection. The keratin forms a scaly plug that blocks the opening of the hair follicle. Usually many plugs form, causing patches of rough, bumpy skin.
Why keratin builds up is unknown. But it may occur in association with genetic diseases or with other skin conditions, such atopic dermatitis. Keratosis pilaris also occurs in otherwise healthy people. Dry skin tends to worsen this condition.