Tinea pedis pathophysiology and treatment.

Fungal infections of the foot can be divided into three major varieties, all of which have differing pathophysiologic aspects with therapeutic implications. Interdigital infections involve an ecological interplay between dermatophytes and bacteria. Simple scaling types of infection are caused by dermatophyte invasion of the stratum corneum, whereas macerated, erosive infections are caused by selection and overgrowth of bacteria, particularly Brevibacterium epidermidis, Micrococcus sedantarius, and various gram-negative species. Bacterial production of methanethiol and other sulfur compounds leads to inhibition of dermatophytes and accounts for the lower recovery of dermatophytes from the most severe cases. Plantar surface infections consist of widespread, moccasin-type infection caused by Trichophyton rubrum and localized scaling infections with episodes of intense inflammation caused by Trichophyton mentagrophytes. The former is particularly associated with an atopic background. Therapy is difficult because of poor immune responses and difficulty in delivering a sufficient quantity of drugs to the lower layers of a thick stratum corneum. Intense inflammation in T. mentagrophytes infections is the result of an immune, contact allergic response to fungal antigens.