DURING the last three decades various investigators have shown that the hydrogen ion concentration of the skin determined in pH units varies between 4-0 and 6-6, depending on site, age, sex and race. Changes of the skin pH can be found in intertriginous areas normally, in dermatological conditions and after the use of alkaline soaps or synthetic detergents.Alkaline soaps and synthetic detergents, apart from their ability to remove dirt from the skin, disturb its "acid mantle " which normally is replaced by the active skin glands. This loss of normal acidity is usually restored within one to two hours. Bernstein and Hermann (1942) found that the usual washing with ordinary soap raised the pH by 1 to 1-5 units and that it took three and a half hours for the normal pH to be restored. Klauder and Gross (1951) found that after ordinary washing the pH was restored to normal in three-quarters to two and a half hours. When excessive washing of the skin (bakers, food handlers, etc.) was performed, the recovery period was prolonged to 19 hours.It is commonly believed that soap may sometimes give rise to dermatitis. It is also over-emphasized that alkaline soaps as cleansing agents in eczema and other inflammatory conditions may produce irritation. Downing (1939) blamed soap and water as the primary hazard in hotel and restaurant workers. Jordan etal.(l 940) described a series of 239 cases of soap dermatitis in housewives. Klauder and Gross (1951) stated that 13 % of their cases of industrial dermatitis were due to soap and water. The exact cause of this effect is not known (Bettley and Donoghue, 1960), but it often arises when they are used in concentrations many times greater than those recommended.The concentration of free alkali was believed to be the most important factor but Klauder and Gross found that alkali sensitivity was an attribute of the eczematous skin and might not be the expression of a selective dysfunction of the skin since the alkali neutralization and sensitivity tests of Burckhardt were positive in patients with diffuse eczem.a unrelated to alkah exposure. Blank (1939) incriminated saturated fatty acids of lower molecular weight as the primary cutaneous irritants. Wilkinson (1962) believed that the disadvantage of soaps in hard water was their facihty for precipitation, resulting in a falling off in efficiency of cleansing. These led to the use of more soap and of greater friction, hotter water, and more immersion, which are the most important factors in the aggravation of an existing inflammatory state. Soap may also * Present address :