Effects of Temperature, Humidity, Minor Injury and Washing on Penetration of Dermatophytes into Human Stratum Corneum

We evaluated the minimum time for penetration of Trichophyton mentagrophytes into human stratum corneum using an experimental model of tinea pedis. After fungal elements were applied on the surface of stratum corneum obtained from a healthy human heel, samples were incubated under designated conditions of temperature and humidity. The penetration of fungal elements was much faster at 35 degrees C than 27 degrees C despite the fact that the latter is an optimal temperature for fungal growth. At 35 degrees C and 100% humidity the minimum time required for penetration was one day. When we applied fungal elements on an abraded surface of stratum corneum, fungi penetrated within a half day under the same conditions. This suggests that minor injury of stratum corneum is a significant factor for infection. The development of tinea pedis does not occur frequently in daily life. We examined the effect of washing the surface of stratum corneum to which T. mentagrophytes had been applied. The samples were incubated under conditions simulating daily life: i.e. with 80% humidity for 8 hours, and 100% humidity for 16 hours. After washing, nearly all the fungal elements had been removed from the surface of stratum corneum within one day. The data suggests that to prevent tinea pedis, daily washing of soles and interdigital regions is effective.