Dermatophytes are eliminated from the skin by a cell-mediated immune reaction. Immunity is acquired by active infection. The inflammatory reaction that ensues may increase the pro-liferatory activity of keratinocytes, causing the fungus to be sloughed from the skin surface. Nonspecific mechanisms of defense prevent invasion into the dermis and bloodstream even in the absence of immunity. Serum inhibitory factor robs fungi of iron, an essential nutrient. The cell walls of the organism activate complement through the alternative pathway and inhibit fungal growth. Polymorphonuclear leukocytes adhere to opsonized and unopsonized hyphae to inhibit growth of the dermatophyte and perhaps damage or kill it. The fungus secretes keratinases and other enzymes that allow the dermatophyte to burrow deeper into the stratum corneum. Mannan from the cell wall of Trichophyton rubrum and a lipophilic toxin associated with it might inhibit cell-mediated immunity and keratinocyte proliferation.