Interdigital athlete's foot: new concepts in pathogenesis.

In our view, interdigital athlete's foot usually begins with invasion of the horny layer by dermatophytes. Because of hot weather, sweating, exercise, or tight shoes, enough moisture accumulates to stimulate an overgrowth of bacteria. Large numbers of normally resident aerobic diphtheroids cause the common wet, macerated type of athlete's foot, while an overgrowth of Gram-negative organisms, such as Pseudomonas and Proteus, is responsible for the more serious cases. The dry, scaly type (dermatophytosis simplex) often alternates with the wet, macerated type (dermatophytosis complex). Flare-ups are common in summer and can be experimentally induced by occlusion of fungus-infected feet. Suppression of bacteria is essential in treating symptomatic athlete's foot. This can be accomplished by exposing the feet to air (eg, wearing sandals) to enhance evaporation of water and prevent the accumulation of excess moisture that stimulates bacterial overgrowth. Topical antibiotics are another approach, with the ideal perhaps being an agent with both broad-spectrum antibacterial and antifungal activity. The newer imidazoles are broad-spectrum compounds but have limited activity against Gram-negative organisms. Our agent of choice, aluminum chloride, combines broad-spectrum antimicrobial activity with chemical drying, a two-pronged attack. We view drying as the decisive element. We doubt that any local treatment can permanently eradicate athlete's foot. Potent antifungal agents can virtually exterminate interdigital dermatophytes, but the inevitable presence of infection in the nails or on the soles assures reinfection. In shoe-wearing populations living in temperate climates, interdigital athlete's foot is mainly a seasonal disease. The various therapies discussed provide a variety of approaches to prevent or ameliorate hot-weather exacerbations.