The
anthropophilic varieties cause forms of
dermatophytosis, that is, fungal infection of the skin. They are keratinophilic: they feed on the
keratin in nails, hair, and dead skin.
Trichophyton concentricum causes "Malabar itch", a skin infection consisting of an eruption of a number of concentric rings of overlapping scales forming
papulosquamous patches.
Trichophyton rubrum and
Trichophyton interdigitale cause athlete's foot (tinea pedis),
toenail fungal infections (a.k.a. tinea unguium, a.k.a. onychomycosis),
crotch itch (a.k.a. tinea cruris), and
ringworm (a misnomer, as there is no worm involved; it is also known as tinea corporis).
Trichophyton schoenleinii cause favus (tinea capitis),
Trichophyton mentagrophytes var. mentagrophytes and
Trichophyton verrucosum cause
kerion (violent reaction results from infection with an animal dermatophytes).
Fungal folliculitis is a rare hair follicle infection induced overwhelmingly by
Trichophyton, which can be spread
zoonotically. The fungi can easily spread to other areas of the body as well and to the host's home environs (socks, shoes, clothes, showers, bathtubs, counters, floors, carpets, etc.). They can be transmitted by direct contact, by contact with infested particles (of dead skin, nails, hair) shed by the host, and by contact with the fungi's
spores. These fungi thrive in warm moist dark environments, such as in the dead upper layers of skin between the toes of a sweaty foot inside a tightly enclosed shoe, or in dead skin particles on the wet floor of a communal (shared) shower. Their spores are extremely difficult to eliminate, and spread everywhere. When the
hyphae of the fungi burrow into the skin and release enzymes to digest keratin, they may irritate nerve endings and cause the host to
itch, which may elicit the
scratch reflex, which directs the host to scratch. Scratching directly transfers fungi and dead skin particles that are infested with the fungi to the fingers and under the finger nails. From there they can be transmitted to other parts of the host's body when the host touches or scratches those. Scratching also damages skin layers, making it easier for the fungi to spread at the site of the infection. If the fungi and infested debris are not washed from the fingers and fingernails soon enough, the fungi can also infect the skin of the fingers (
tinea manuum), and burrow underneath and into the material of the fingernails (
tinea unguium). If left untreated, the fungi continue to grow and spread. ==Treatments==