Pseudofolliculitis barbae (PF) is a dermatological disorder affecting approximately 50%. of black men who shave. The disease is characterized by ingrown hairs and attendant papules, pustules or vesicles ("razor bumps") which can occur over the entire beard area but which are most prevalent in the submandibular region. While it is generally accepted that the disease is of biological origin, PF appears to be triggered by shaving which in turn leads to the immediate cause of the disorder, ingrown hair formation. However, differences of opinion exist as to the basic etiology of PF--that is, how ingrown hair formation occurs in certain individuals and not others. Therefore a comparison of the skin, hair and post-shave beard hair regrowth patterns of "normal" and PF-prone black and white men by scanning electron microscopic (SEM) examination of polyethylene replicas was undertaken to determine the causes of ingrown hair formation.