The effects of epilation and hormones on the activity of rat hair follicles.

The growth of hair from epilated and non-epilated areas of rats receiving a variety of hormonal treatments was investigaged by pulse-labelling with 35-S-cystine. While epilation at certain stages of the spontaneous cycle may rephase follicular activity, it did not affect the length, rate or duration of growth of the hairs which erupted subsequently, either in untreated or hormone-treated rats. Thyroxine shortened the active as well as the resting phase of the follicular cycle. It also increased the growth rate, so that hairs were ultimately the same length as those from untreated animals. Estradiol slightly shortened the duration of the active phase, even though the complete cycle was prolonged. It also decreased the hair growth. When administered simultaneously, estradiol and thyroxine exerted their effects independently.