Relation of Hair Proliferation to Damage Induced in the Mouse Skin

Abstract

Conclusions

The combined treatment of methylcholanthrene-in-benzene painting plus 1000 r irradiation results in changes in the epidermis which are more severe than those occurring after either treatment alone. Sebaceous glands are destroyed by methylcholanthrene and redifferentiate only when hair growth is active. Where hair development is arrested or delayed by the irradiation, there is a failure of new sebaceous glands to redifferentiate until hair development again occurs. Furthermore, the initial damage to the epidermis in terms of hyperplasias and hyperkeratoses is less in areas where hairs were in anagen IV at the time of the single or combined treatment. Maximal damage occurs in telogen areas. Not only, then, is active hair proliferation associated with restoration, as in the case of sebaceous glands, but it also protects the epidermis from damage and it is associated with the repair of epidermal damage.

The explanation of such phenomena is as yet incompletely known. Cells of the external sheath of the follicle are directly involved in redifferentiation of sebaceous glands and to a considerable extent in repair of the epidermis. This layer of external sheath cells forms the morphological continuity between the hair germ or bulb and the basal layer of the epidermis. The resistance of epidermis to damage, as well as the capacity for repair, which are associated with hair proliferation may well indicate a comparable functional continuity of the external sheath. In any case, the importance of considering and controlling conditions in the skin at the time of and after treatments is obvious.