Irritant actions of unphysiological pH values. A controlled procedure to test for topical irritancy.

The abdominal skin of juvenile white mice was used. Topical application was accomplished by intracutaneous injection. The solutions tested were thoroughly standardized. By using a special buffer system, a mixture of histidine glutamate and lysine glutamate, each pH value could be tested with the same buffer capacity. The pH values varied from pH 3 to pH 11, the solutions being always iso-osmolalic with plasma. Two criteria were used to judge the irritancy: (a) the edematous reaction for the first 6 h and (b) the macroscopic aspect after 24 h. A very special procedure enabled us to obtain objective numerical values for criterion (a). The results disclose that irritation becomes manifest at pH 4 and pH 10, becomes clear-cut with pH 3 and even more so with pH 11, and depends strongly on the buffer capacity employed. With two substances-amidosulfuric acid and (tri) sodium phosphate--it was exemplified how the procedure could be used to routinely screen for topical irritancy in an informative, inexpensive and decent manner.