STINGING CAPACITY OF APPLIED SUBSTANCES 203 stripped skin. The first test was carried out on the backs without sweating and on the cheeks after 15 rain of sweating. Stinging did not occur on normal skin. On the stripped sites of the back, as well as the cheek intense immediate stinging developed, disappearing within about a minute. Stripping practically eliminates the distinction between stingers and nonstingers. It should also be noted that almost as severe stinging occurred after application of the ve- hicle, 95 per cent alcohol. It had become evident by this time that the difference between stingers and nonstingers was merely quantitative. To test this idea, 5, 10, and 15 per cent ADP was applied on separate occasions to the profusely sweating cheeks of 3 stingers and 3 nonstingers. The stingers experienced sharp discomfort with 5 per cent ADP the sevek'ity and duration of stinging increased progressively with the 10 and 15 per cent concentrations. With the latter, the distress was not appreciably reduced by leaving the chamber. As expected, 5 per cent ADP had no effect on nonstingers. All 3, however, experienced slight stinging with 10 per cent, while with 15 per cent, 2 of the 3 had moderate stinging. It is clear, then, that stingers merely have lower thresholds. When the stimulus is great enough, even nonstingers will experience mild to moderate stinging. We have repeatedly observed this phenomenon with other drugs at higher concentrations. VIII. REGIONAL DIFFERENCES Five per cent ADP was used on 3 stingers to compare the intensity of stinging in the following regions: central cheek, nasolabial fold, forehead, chin, infraorbital and retroauricular regions, axilla, antecubital fossa, upper back, and scalp. The applications were made after the subjects had been sweating for 15 min. Clear-cut stinging was restricted to the face, being most pronounced on the nasolabial fold, followed by the cheek, chin, infraorbital, and retroauricular region. The forehead reaction was marginal. Stinging was not perceived on the scalp, back, arm, and axilla. These findings conform to those of Weigand and Mershon (6) using tear gas 0-chlorobenzylidene malononitrile (CS) as the stinging agent. Stinging is pre- dominantly a facial phenomenon. IX. CORRELATION OF STINGING WITH IRRITANCY A. c•-hydroxy acids.' The test agents were: lactic acid, pyruvic acid, tartaric acid, and glycolic acid. Five per cent aqueous solutions were evaluated in 3 stingers at different sweating sessions. Comparative irritancy was determined by 24-h occlusive patch tests on the forearms with 5 and 15 per cent concentrations of the respective acids on the same subjects. The intensity of the reaction was scored on a 0 to 3 scale (0 = no erythema I = slight 2 = moderate and 3 = severe). The rank order of descending irritancy was: pyruvic glycolic tartaric lactic.

204 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The first 2 produced severe erythema and vesiculation with the 15 per cent concentra... tion. The rank order was the same in stinging tests the correlation was thus very good despite the small size of the sample. pH does not account for these differences (range 1.7 to 2.0). Laden (4) also found that acids of the same pH had quite different stinging capacities. Following his precedent, we compared equimolar (0.3 N) solutions (concentration percentages 2.25 to 2.70). The rank order of stinging was identical, although, stinging tended to be rather weak at these lower co ncentrations. I3. Esters ofp-aminobenzoic acid.' The test agents were glyceryl p-aminobenzoic acid (Gpi •:.•i• :I Escalol 106), (ADP-Escalol 506), and octyl-dimethyl-paba (OCP-Escalol 507). Five perljii" cent solutions in ethanol were tested for stinging in the usual manner on 3 subjects. Five per cent solutions were evaluated for irritancy by occlusive patch tests on the"•: forearm after criss-cross scarification of the skin with a 27-gauge needle. Applications .: were made daily for 3 consecutive days under cutaneous occlusion. : :: As usual, ADP induced sharp stinging. The other 2 esters lacked this property com, il pletely. GP caused modest redness while ADP and ODP were completely innocuous on sacrifled skin. So, in this instance, a stinging ester (ADP) was found to be nonirritating, while an irri-'. rating one (GP) was nonstinging. 5' C. Metalh'c antiperspirants: The test agents were aluminum chloride hexahydrate, alu-:: minum chlohydroxide, aluminum bromhydroxide (basic aluminum bromide), and zir-i conium hydroxychloride. Thirty per cent aqueous solutions of these were evaluated for irritancy by 24-h occlusive patch tests on forearm skin. This same concentration was , also used in stinging tests performed on 3 stingers. The rank order of irritancy was: ß minum chloride zirconium hydroxychloride aluminum chlorhydroxide equals i::• basic aluminum bromide. ß The last two caused no skin reaction, whereas the first two produced erythema and'::!:: ß : small pustules, aluminum chloride being somewhat more severe. As with hydroxy acids, stinging capacity paralleled irritancy. Aluminum chlorideii :i caused slight stinging, followed closely by zirconium hydroxychloride, while the other./ 2 salts lacked this property altogether. D. Effect of strong irritants.' A•'5 per cent aqueous solution of sodium lauryl sulfate produced an intense dermatitis in a 24-h patch test on the forearm of 3 stingers, still this same solution did not induce stinging in any sweating subject when applied to the: face. • Undiluted kerosene caused blisters in a 24-h patch test on the same 3 persons, but was•:: I. utterly without stinging potentiality. . A 5 per cent solution of Hyamine 3500 produced a marked irritant reaction by a 24 ' hr occlusive patch test. It, too, failed to elicit stinging. It is thus apparent that strong irritants may be completely free of stinging capacity.