The genital areas and the exposed areas such as the eyelids, forearms, face and neck are more prone to it.
The cells of the epidermis (the surface layer of the skin) are normally protected from damage by the tightly packed squamae of keratin of the horny layer. The elasticity of keratin varies with its water content. This water content can be reduced by evaporation or by removal of the lipid with which it retains moisture. Substances which produce inflammation of the epidermis or dermatitis by mechanical or chemical disruption of the horny layer are called irritants.
Degreasing agents like soaps, if used too frequently over a short time, will cause dryness, redness, fissuring and irritation of the skin in almost everyone.
Certain medications applied externally such as atropine, belladonna, carbolic acid, iodine, mercury, penicillin, sulphonamides, sulphurs, tars and turpentine sometimes cause dermatitis. Other substances are hair dyes, bleaches, skin tonics, nail polish, perfume, wool, silk, nylon, floor-wax and various detergents. Deficiency of vitamin A and pantothenic acid, and nervous and emotional stress can also cause it.