Dermatophytes are a highly specialized group of fungi that break down keratin -- the protein the makes up hair and nails -- and absorb its nutrients. One dermatophyte in particular -- trichophyton rubrum -- reportedly is responsible for than 80% of onychomycosis (tinea unguium), 96% of athlete's foot infections (tinea pedis), 90% of jock itch infectios (tinea cruris), and more than 50% of ringworm infections of the body (tinea corporis).