Mycoses are caused by dermatophytes, which belong to the imperfect fungi (Fungi imperfecti ). Dermatophytes include about 40 species belonging to 3 genera: Trichophyton , Microsporum and Epidermophyton. Dermatophytes have the mycelial part (mycelium) that grows into the ground and serves to collect nutrients and spores (conidia). Fungi occur in one of the three developmental stages: asexual saprophytic (in soil), sex saprophytic (in soil), always asexual (in host) parasitic stage. Dermatophytes form hyphae or fragments of mycelium on the skin and hyphae and arthospores on the outside or inside of the hair. The infectious form of the fungus are spores – arthospores and hyphae. Artrospores are resistant to adverse environmental conditions and can survive up to two years in the environment. The main source of mycoses are indirect infections through infected epidermis or hair. Dermatophytes produce keratinases and other proteolytic enzymes that enable them to hydrolyze keratin, the main protein that is part of the hair, nails and skin, as well as other skin components. They use keratin as a source of carbon and energy, and thus only colonize dead skin elements. Living tissues are not infected, but fungi can provoke a cellular immune response that can lead to the destruction of living tissues.

A type of dermatophyte that mainly affects hair and skin, causing microbial mycosis. Its characteristic symptom is single or multiple round or oval foci of various sizes with evenly broken hair, which are covered with gray, finely flaky epidermis. The skin in the foci of infection usually shows no signs of inflammation.

Dermatophytes from Trichophyton genus cause mycoses in both animals and humans. These dermatophytes are one of the main causes of human, skin and nail infections. The most common clinical forms of zoonotic infections are deep mycosis of scalp and chin and mycosis of smooth skin.

Fungi species of the genus Nannizzia are geophiles. Sometimes these dermatophytes may infect animals or humans.