Dr. Greene's Answer
Keratosis pilaris is a common mild condition in which the backs of the upper arms look rather like dried out, plucked chicken flesh. Sometimes it is referred to as KP or follicular keratosis. Keratosis pilaris is hereditary.
The characteristic rash is caused by firm little plugs forming in the hair follicles. The plugs themselves are made of bits of keratin, the main protein found in the outermost protective layer of skin (thus the name keratosis). These plugged follicles give the skin a raised, stippled appearance — usually called goosebumps. The bumps are usually skin color or slightly pinker, and do not itch. The rash is often not noticeable to others, except on close inspection.
Classically, the condition appears in early childhood, often around the age of two or three. Since the rash is associated with and worsened by dryness of the skin, most people experience a clear-cut seasonal variation — generally worse in the winter. Although the rash changes in intensity from time to time, the baseline usually stays the same until middle adolescence, when it begins to improve. Adults who still have keratosis pilaris often experience further improvement during the middle decades. The average age when spontaneous improvement is first noted is sixteen (British Journal of Dermatology, June 1994).
Although keratosis pilaris is hereditary, the rash is more common in those with eczema, dry skin, or vitamin A deficiency (or a number of more esoteric skin conditions). The most common spot on the body for keratosis pilaris is the backs of the upper arms (92% of affected people have it there). Next most common is the thighs (59%) (British Journal of Dermatology, June 1994). It can also occur on the face, buttocks, and eyebrows.