Optimal patch application time in the evaluation of skin irritation

Abstract

We investigated the optimum application for evaluating skin irritation response by using samples of irritants commonly used as additives in cosmetics and other common household products. We studied 47 volunteers (16 men and 31 women). We selected three types of surfactant, one moisturizer, one anti-infective agent and one oil solution. Using Finn chambers on Scanpor tape, we performed the patch test. A total of 0.015mL of each sample was applied to the Finn chamber. For liquids, circular filter paper was soaked in 0.015mL of the sample. Samples were placed on the upper back of participants, and closed for 4, 24 or 48h. A patch application time of 24h is sufficient to detect primary skin irritation from irritants in cosmetics and other common household products. In addition, we found that skin irritation reactions were strongest at 24h after patch removal and that the reaction tended to be weaker at 48h after patch removal. Patch testing to evaluate irritants should be performed by means of a 24-h patch test with a follow-up reading at 24h after patch removal. An application time of 24h places less of a burden on patients than a 48-h patch test.