[Threshold of contact allergy to stearamidoethyl diethylamine in guinea pigs].

The cationic surfactant, stearamidoethyl diethylamine (SD) is an emulsifier used in topical medications and cosmetics. It has been reported to cause allergic contact dermatitis. This report concerns a study of the sensitizing capacity of SD in guinea pigs, using the modified maximization method (8) and closed epicutaneous test (10); the induction concentration was 10% in petrolatum. By the modified maximization method, 8 of 20 (40%) of the guinea pigs were sensitized to 1% SD, mean response 1.9; and 6 (30%) to 0.5% SD, mean response 1.4. In closed epicutaneous tests, 3 of 20 (15%) guinea pigs also showed reactions to 1%, and 2 of 20 (10%) to 0.5% SD. The results from modified maximization test showed that SD is a moderate sensitizer, as the sensitizing rate is in the range of 26-50% (below 26% is classified as "mild", and above 50% is "strong"). Even with a less sensitive closed epicutaneous test, its sensitivity could also be detected. From a risk-benefit point of view, no substantial risk for cosmetic chemicals intended for extensive use on normal and diseased skin will be accepted. Drugs may be acceptable, in spite of their sensitizing potential, because of their inherent benefit. As such, this surfactant may be only suitable in prescription drugs. Allergic contact dermatitis is rarely reported from cationic surfactants. Lack of suspicion of these not-necessarily-innocent chemicals has been partially responsible. The potential widespread use of emulsifiers with sensitizing capacity warrants further surveillance, as does the possibility of cross reaction between various emulsifiers.