There have been several reports demonstrating that the pilosebaceous unit reacts to experimental injury1-4 of the skin. The basis for the changes seen in the pilosebaceous unit in naturally occurring diseases has not been appreciated. Specific diagnostic histologic findings are rare in the pilosebaceous unit, but secondary changes are quite common. One of the few studies to appreciate this is the excellent report by Pinkus5 clearly demonstrating inverted cone-shaped hyperplasia of the intraepidermal portion of the pilosebaceous unit in senile keratosis.
The purpose of this report is to further delineate the secondary changes of the pilosebaceous unit that occur in various cutaneous diseases. Particular emphasis will be placed on the changes involving the upper portion of the follicle and the sebaceous apparatus, for two reasons. First and most important is that most of the specimens examined were from areas containing only velus hairs. Since these hairs are characterized