786 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The disadvantage of formaldehyde is its well-known sensitization action after repeated application. The authors feel, however, that it should be pos- sible to employ low concentrations (about 1%) in routine use especially with the assumption that this anhidrotic agent is applied repeatedly. •4/uminium Chloride is currently one of the most widely used anhydrotic agents and possesses some advantages over formaldehyde. It has a lower sensitizing potential but is more of a primary irritant due to its acidity in an aqueous medium. There is no unanimity in explaining its antiperspirant action. Denaturation and astringent action which could cause mechanical constriction of the eccrine sweat ducts similar to formaldehyde have been described (20) (21). This concept is confirmed also by recent findings of the authors of this paper. In addition degenerative changes, primarily of the apocrine glands, have been described (22). Recently, Papa and Kligman have carefully studied this complex of problems. They conclude that the anti- perspirant influence of aluminJure chloride is caused by increased sweat resorption during passage through the eccrine ducts as a consequence of periductal changes due to aluminium chloride (19). Gordon and Maibach conclude that the changes take place below the level of the horny layer (25). The authors believe that different conclusions can follow from different experimental approaches. For example, the concentration of aluminium chloride is of great importance. The manner and the rate of penetration depend furthermore on the degree of filling of the eccrine sweat ducts by sweat, on the temperature conditions of the subject (sub-treshold thermal excitation and season of the year), and on the period of exposure to the active anhidrotic. If sweating occurs in the test area, aluminium chloride can conceivably penetrate via the eccrine ducts thus degenerative changes in the vicinity of the eccrine duct and possibly even in the coiled duct of the sweat gland may occur. Chances for this are especially good in the axillary region, in view of the artatomic course of the eccrine sweat duct and in view of the fact that here, as also on the palm, psychic sweating is almost continuous. One must also take into account the influence of resorption in the axillary region in a manner similar to that under conditions of partial occlusion. Zinc chloride is employed relatively rarely as an antiperspirant at this time. Its action is that of a slow astringent and the mechanically constricted eccrine sweat ducts can be opened by stripping with adhesive tape. Hexameth•ylene tetramine causes no suppression of sweating even after 10 hours of application. The anhidrotic effect of hexamethylene tetramine depends on the liberation of formaldehyde vapors in the presence of acid-

COMPARISON OF THE EFFECTIVENESS 787 reacting sweat (17) (23) and can thus occur only in a sufficiently acidic and moist environment which is required for its hydrolysis. Thus, on the volar side of the forearm, where there is no sweating under normal temperature conditions, it exhibits no anhidrotic effect. Sodium hexametaphosphate and the metaphosphate po•mer are used as bath additives with antiperspirant action (Calgon ©, Dulgon ©) (17) (23). From our measurement it is concluded that these materials by themselves have no antiperspirant effect. They act instead as agents which accelerate the penetra- tion of water into the horny layer and thus can assist the penetration of simultaneously or subsequently applied antiperspirants (powders with zinc oxide, boric acid, salicylic acid, etc.). It the bath lasts very long, they can cause temporary constriction or closure of the eccrine s•veat duct through swelling of the periporal horny layer. Distilled water applied to the forearm skin as the control causes, depending on the period of skin moistening, increased sweat expulsion in the test area after a given period of drying. This certainly is not direct stimulation of the sweat gland. On the other hand, one could attribute this effect to hydration (plasdcization) of the horny layer which surrounds the sweat gland outlets. The inside dimensions of the outlets regulate the rate of passage of sweat through the eccrine ducts and thereby the quality and the quantity of the expelled sweat and to a degree also the activity of the sweat gland via feed- back (33). Prolonged increased hydradon even after termination can lead to changes in the sorptive capacity and sweat diffusion within the periporal horny layer perhaps as a result of the elution of water-binding substances. The authors have shown changes on the epidermal surface after maceration in water by microtopographical prints (29), and these are confirmed by their results from perspiration print tests (Fig. 5 D, E, F). Excessive hydration with total prevention of water evaporation (occlusion) leads, after a period of time, to swelling of the horny layer which includes the periporal rings which can lead to a temporary stoppage of sweating via hidromeiosis. Maceration lasting longer than 48 hours leads to irreversible denaturation changes in the horny layer (34). CONCLUSIONS From the above results it can be concluded that the tested antiperspirants can be rated with regard to their effectiveness for sweat reduction as follows: Formaldehyde aluminium chloride zinc chloride. Perspiration print tests, microtopographical observations of the epidermal surfaces, and the reversal of hypo- and even anhidrosis by stripping lead to