Causes

Keratosis pilaris is caused by the buildup of keratin — a hard protein that protects skin from harmful substances and infection. The keratin blocks the opening of hair follicles, causing patches of rough, bumpy skin.

It's not clear why keratin builds up in people with keratosis pilaris. It may occur in association with a genetic disease or with skin conditions such as atopic dermatitis. Dry skin tends to make keratosis pilaris worse.