The effect of X-ray irradiation upon the epithelial melanin unit of the hair bulb in hooded rat.

A marked increase in the quantity of pigment in the upper bulb, penetration of melanosomes into the papillae and vacuolisation of the bulb keratinocytes occurred as early as 4--6 h after irradiation with a dose 600--1200 R. Afterwards considerable hyperpigmentations appeared in the proximal segments of dystrophic and catagen hairs and melanin was found in the catagen columns and beyond them. In most animals within 4--6 h after irradiation occurred a distinct vacuolisation of the Malpighian layer and the granular layer became more prominent.