[Experimental studies on the penetration into the human stratum corneum of the dermatophyte]

We present results on the experimental penetration of Trichophyton mentagrophytes and T. rubrum under designated condition of humidity into human stratum corneum obtained from a healthy human heelregion. When mycelia were applied to the surface side of stratum corneum and then incubated at 100 % humidity, T. mentagrophytes and T. rubrum were observed in the stratum corneum on day 1 and day 1.5, respectively. At 95% humidity, T. mentagrophytes and T. rubrum penetrated on day 1.5 and day 4, and at 90% humidity, they penetrated on day 3 and day 7, respectively. At less than 85% humidity, no fungal elements of either strain were observed in stratum corneum for up to 7 days. These datasuggest that at least 90% humidity is necessary for these two fungi to penetrate into stratum corneum within a few days. However, when T. mentagrophytes was applied to the cutting side of the stratum corneum and thenincubated at more than 70% humidity, the mycelia were able to penetrate within a day. The same results were obtained when T. rubrum was applied on the cutting side and incubated at 95 and 100% humidity. T. rubrum was also able to penetrate into the stratum corneum within several days at 70 and 80% humidity. These results may indicate that not only persistent moisture but also minor injuries of stratum corneum are the most important factors in the development of tinea pedis.