Cell death (apoptosis) in hair follicles and consequent changes in the width of hairs after irradiation of growing follicles.

Irradiation of anagen (growing) hair follicles results in a dose-dependent increase in the number of histologically identifiable fragments of dead cells (apoptotic fragments). The incidence of apoptotic fragments is linearly related to dose, increasing at a rate of 2.92 fragments per follicle section per Gy. The effects of doses of 0.2 Gy can be easily detected. Subjective attempts to associate clusters of fragments with dead or dying cells suggests that the number of fragments per cell increases with dose (about 1.7 fragments per cell after 1 Gy to about 2.7 fragments per cell after 5 Gy). There is a natural incidence of cell death in controls (0.13 +/- 0.06 fragments per follicle section with about 1.4 fragments per dead or dying cell). Damage to the follicle cells is expressed in the differentiated product of the follicle, the hair, by a reduction in width. This is probably the cellular basis for the production of dysplastic hairs. The hair width has been measured and is reduced by about 7 per cent for every gray of radiation. The value of the hair and hair follicles as potential biological dosimeters is discussed.