The quantitative assessment of topical irritancy and its application to unphysiological pH-values.

Injection of aqueous solutions of topically irritant substances intracutaneously into the skin of juvenile white mice creates a persisting oedema which can be assessed by the number of wrinkles formed upon reefing the skin at the site of injection. An algorithm is presented which transforms the number of wrinkles recorded just before as well as 2.5 h and 6 h after injection into the intensity of the oedematous reaction. The results obtained with a collective of about 10 mice per solution to be tested are reliable and reproducible; they conform to dose-response relations and hence can serve for quantifying local irritancy. The method is used to investigate the effect of pH, and a general model is developed describing the local irritancy of unphysiological pH-values.