COMPARISON OF THE EFFECTIVENESS 785 of an unmoistened area. On the perspiration prints, one can also see an in- crease of the large polymorphal spots which are formed by the inhibition of expelled sweat in a periporal relief which is altered by water moistening lasting for varying times. DISCUSSION From the above results it follows that, amongst the tested materials, formaldehyde is the most effective anhidrotic even at low concentrations and after short exposure periods. By denaturing the proteins of the horny layer it causes mechanical constriction or even closure of the terminal portion of the eccrine sweat duct (so-called high level blockage) (19) (20). Such microstructural contractive changes of the epidermal surfaces of the palm and the forearm have been verified with the aid of silicone rubber prints by the method of Sarkany and Caron (28) (29). The intensity and depth of denaturation of the epidermal surface are proportional to the concentration of and the exposure time to formaldehyde (3). This is also confirmed by the gradual regeneration of sweating with successive stripping. Denaturation causes modification of the physico-chemical properties of the horny layer and is the cause of varying adhesivity to the stripping tape as a result, no mechanical failure of the barrier takes place even after a large number of strippings. Mechanical occlusion of the eccrine sweat duct with simultaneously unreduced activity of the sweat gland effects changes in the water circulation in the skin and leads to dilatation of the eccrine sweat ducts in their epidermal sections (30) (31) (32). The period, during which sweating is stopped or reduced, depends on the rate of epidermal regeneration as a result of its uninterrupted renewal (horny layer--approximately 6 days, whole epidermis--26 to 30 days) (2). Explications to A) Construction to impermeability of most eccrine sweat ducts. Longitudinal elongation of dark spots demonstrates the constriction of eccrine sweat ducts to B) Changes after aluminium chloride treatment are the same as those for formaldehyde (longi- tudinal constriction to closure of a large number of eccrine sweat ducts) to C) The contours of most detected eccrine sweat ducts are round and wide open which corres- ponds to their morphological structure in the deeper portions of the horny layer. There is no pronounced imbibition of sweat into the periporal relief to D) Polymorphous, mostly isolated minute black spots with marked small dendritical spines to E) Larger, polymorphous spots with interconnected spines in the periporal relief to F) Intensely black, polymorphous spots, the maiority of which is interconnected with the surrounding spots into large merged groups.

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-