Keratosis pilaris is a common skin disorder in which a protein found in the skin called keratin forms hard plugs within the hair follicles (tiny pockets beneath the skin from which hair grows).

In the normal development of skin, cells produce keratin, which forms the upper layers of the skin, nails and hair. The cells and keratin eventually move toward the outermost layer of the skin (called the stratum corneum) and then die and flake away.

In keratosis pilaris, the keratin does not flake off, but clogs the hair follicles and forms small bumps. The bumps usually resemble goose bumps or chicken skin and are the texture of coarse sandpaper. They can be found almost anywhere on the body (except the soles of the feet and palms), but are most common on the upper arm, buttocks and thighs. In some cases, bumps appear on the face. This is especially common in children. In extreme cases, the condition may also affect the chest and back. 

There are several different types of keratosis pilaris, including:

• Keratosis pilaris rubra. Characterized by red, inflamed bumps.
  
  
• Keratosis pilaris alba. Characterized by rough, bumpy skin with no irritation.
  
  
• Keratosis pilaris rubra faceii. Characterized by a reddish rash on the cheeks.

According to the American Academy of Dermatology, up to 40 percent of the population has keratosis pilaris. It can affect people of any age, but it is most common in children and found more often in girls. Because dry skin exacerbates the condition, it is usually worse during the winter and often clears up during the summer when humidity reduces the severity of dry skin. However, some patients flare-up with the summer heat. Women with the condition may also develop an increase in the severity of their symptoms during pregnancy or following childbirth.

Keratosis pilaris is a benign (harmless) condition. However, in some cases, patients may be distressed by the appearance of the skin.

The cause of keratosis pilaris is unknown, but it seems to be hereditary. It is also more common in overweight individuals and patients with atopic dermatitis, the type of eczema (chronic, itchy inflammation of the upper layers of the skin) caused by allergies.

Keratosis pilaris is sometimes confused with acne. The bumps usually do not itch or cause pain. Sometimes, a small, coiled hair can be seen beneath a bump.

Other signs and symptoms include:

• Skin with fine, bumpy texture
• Skin–colored bumps that are the size of a grain of sand
• Slight pinkness around some of the bumps