This common condition is inherited as an autosomal dominant trait, and is possibly caused by mutations in a gene lying on the short arm of chromosome 18. The abnormality lies in the keratinization of hair follicles, which become filled with horny plugs.
The changes begin in childhood and tend to become less obvious in adult life. In the most common type, the greyish horny follicular plugs, sometimes with red areolae, are confined to the outer aspects of the thighs and upper arms, where the skin feels rough. Less often the plugs affect the sides of the face; perifollicular erythema and loss of eyebrow hairs may then occur. There is an association with ichthyosis vulgaris.
Involvement of the cheeks may lead to an ugly pitted scarring. Rarely, the follicles in the eyebrows may be damaged with subsequent loss of hair there.
A rather similar pattern of widespread follicular keratosis (phrynoderma) can occur in severe vitamin deficiency. The lack is probably not just of vitamin A, as was once thought, but of several vitamins.
None are needed.
Treatment is not usually needed, although keratolytics such as salicylic acid or urea in a cream base may smooth the skin temporarily.