Harvard Women's Health Watch

By the way, doctor: What is keratosis pilaris?

Q. Ever since my teens, I've had a rash that looks like goose bumps on my arms and legs. My doctor says it's keratosis pilaris. What do you know about this condition?

A. Keratosis pilaris is a harmless skin condition characterized by tiny bumps on the back of the upper arms, the front of the thighs, the buttocks, and sometimes the cheeks of the face. The bumps are about the size of pinheads and evenly spaced. They are usually skin-colored or whitish-gray and may be individually ringed in red. The affected area may feel rough, like coarse sandpaper or "gooseflesh." The condition affects as many as 40% of adults — women more often than men. It usually begins in childhood and worsens during puberty, but — thankfully — it often improves in adulthood.

Keratosis pilaris is caused by an excessive buildup of keratin, a protein found in skin, hair, and nails. The keratin forms hard plugs in the openings of sebaceous glands adjacent to hair follicles, blocking the follicle openings and producing the characteristic bumps. Experts don't know why this buildup occurs in some people but not others. The condition tends to run in families, and genetic factors are probably involved. It's also more common in people with either of two other skin conditions — eczema and ichthyosis vulgaris — both of which are characterized by very dry skin. Keratosis pilaris tends to get worse in dry, cold weather and improve when warmth and humidity increase.

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