Keratosis pilaris is a common, harmless skin condition. It causes small, hard bumps that may make your skin feel like sandpaper. The bumps are often light-colored. They usually appear on your upper arms, thighs, and butts, sometimes with redness or swelling. They can also show up on your face, but that’s less common. Except for some itching, keratosis pilaris doesn’t hurt and doesn’t get worse. Many children and teens get it, and it usually disappears as they get older.
Keratosis pilaris is caused by a buildup of keratin, the protein that protects skin from infections and other harmful things. The buildup forms a plug that blocks the opening of a hair follicle, but doctors don’t know what triggers the buildup.
If you have dry skin, you’re more likely to have keratosis pilaris. It’s usually worse in the winter months, when there’s less moisture in the air, and then may clear up in the summer.