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Dermatophyte (from Greek language δέρμα derma "skin" (Genitive case δέρματος dermatos) and φυτόν phyton "plant"), . is a common label for a group of fungus of Arthrodermataceae that commonly causes skin disease in animals and humans. Traditionally, these anamorphic (asexual or imperfect fungi) mold genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera. Species capable of reproducing sexually belong in the teleomorphic genus Arthroderma, of the Ascomycota (see Teleomorph, anamorph and holomorph for more information on this type of fungal life cycle). As of 2019 a total of nine genera are identified and new phylogenetic taxonomy has been proposed.
Dermatophytes cause infections of the skin, hair, and nails, obtaining nutrients from material. The organisms colonize the keratin tissues causing inflammation as the host responds to metabolic byproducts. Colonies of dermatophytes are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate the viable tissue of an immunocompetent host. Invasion does elicit a host response ranging from mild to severe. Acid (proteases), (2025). 9780071669047, McGraw-Hill Medical. ISBN 9780071669047 elastase, , and other proteinases reportedly act as virulence factors. Additionally, the products of these degradative enzymes serve as nutrients for the fungi. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection.
Some of these skin infections are known as ringworm or tinea (which is the Latin word for "worm"), though infections are not caused by worms. (2018). 9781259644047 ISBN 9781259644047 It is thought that the word tinea (worm) is used to describe the snake-like appearance of the dermatophyte on the skin. Toenail and fingernail infections are referred to as onychomycosis. Dermatophytes usually do not invade living tissues, but colonize the outer layer of the skin. Occasionally the organisms do invade subcutaneous tissues, resulting in kerion development.
Although symptoms can be barely noticeable in some cases, dermatophytoses can produce "chronic progressive eruptions that last months or years, causing considerable discomfort and disfiguration." Dermatophytoses are generally painless and are not life-threatening.
The infection can be seen between toes (interdigital pattern) (2025). 9780071772969, McGraw-Hill Education/Lange Medical Books. ISBN 9780071772969 and may spread to the sole of the foot in a "moccasin" pattern. In some cases, the infection may progress into a "vesiculobullous pattern" in which small, fluid-filled blisters are present. The lesions may be accompanied by peeling, maceration (peeling due to moisture), and itching.
Later stages of tinea pedis might include hyperkeratosis (thickened skin) of the soles, as well as bacterial infection (by streptococcus and staphylococcus) or cellulitis due to fissures developing between the toes.
Another implication of tinea pedis, especially for older adults or those with vascular disease, diabetes mellitus, or nail trauma, is onychomycosis of the toenails. Nails become thick, discolored, and brittle, and often onycholysis (painless separation of nail from nail bed) occurs.
The rashes appear red, scaly, and pustular, and is often accompanied by itch. Tinea cruris should be differentiated from other similar dermal conditions such as intertriginous candidiasis, erythrasma, and psoriasis.
The fungi use various proteinases to establish infection in the keratinized stratum corneum. Some studies also suggest that a class of proteins called LysM coat the fungal cell walls to help the fungi evade host cell immune response.
The course of infection varies between each case, and may be determined by several factors including: "the anatomic location, the degree of skin moisture, the dynamics of skin growth and desquamation, the speed and extent of the inflammatory response, and the infecting species."
The ring shape of dermatophyte lesions result from outward growth of the fungi. The fungi spread in a centrifugal pattern in the stratum corneum, which is the outermost keratinized layer of the skin.
For nail infections, the growth initiates through the lateral or superficial nail plates, then continues throughout the nail. For hair infections, fungal invasion begins at the hair shaft.
Symptoms manifest from inflammatory reactions due to the fungal antigens. The rapid turnover of desquamation, or skin peeling, due to inflammation limits dermatophytoses, as the fungi are pushed out of the skin.
Dermatophytoses rarely cause serious illness, as the fungi infection tends to be limited to the superficial skin. The infection tends to self-resolve so long as the fungal growth does not exceed inflammatory response and desquamation rate is sufficient. If immune response is insufficient, however, infection may progress to chronic inflammation.
Infection may become chronic and widespread if the host has a compromised immune system and is receiving treatment that reduces T-lymphocyte function. Also, the responsible species for chronic infections in both normal and immunocompromised patients tends to be Trichophyton rubrum; immune response tends to be hyporeactive . However, "the clinical manifestations of these infections are largely due to delayed-type hypersensitivity responses to these agents rather than from direct effects of the fungus on the host."
Additionally, a Wood's lamp examination (ultraviolet light) may be used to diagnose specific dermatophytes that fluoresce. Should there be an outbreak or if a patient is not responding well to therapy, sometimes a fungal culture is indicated. A fungal culture is also used when long-term oral therapy is being considered.
Fungal culture medium can be used for positive identification of the species. The fungi tend to grow well at 25 degrees Celsius on Sabouraud agar within a few days to a few weeks. In the culture, characteristic septate hyphae can be seen interspersed among the epithelial cells, and the Conidium may form either on the hyphae or on conidiophores. Trichophyton tonsurans, the causative agent of tinea capitis (scalp infection) can be seen as solidly packed arthrospores within the broken hairshafts scraped from the plugged black dots of the scalp. Microscopic morphology of the conidium is the most reliable identification character, but both good slide preparation and stimulation of sporulation in some strains are needed. While small microconidia may not always form, the larger macroconidia aids in identification of the fungal species.
Culture characteristics such as surface texture, topography and pigmentation are variable, so they are the least reliable criteria for identification. Clinical information such as the appearance of the lesion, site, geographic location, travel history, animal contacts and race is also important, especially in identifying rare non-sporulating species like Trichophyton concentricum, Microsporum audouinii and Trichophyton schoenleinii.
A special agar called Dermatophyte Test Medium (DTM) has been formulated to grow and identify dermatophytes. Without having to look at the colony, the hyphae, or macroconidia, one can identify the dermatophyte by a simple color test. The specimen (scraping from skin, nail, or hair) is embedded in the DTM culture medium. It is incubated at room temperature for 10 to 14 days. If the fungus is a dermatophyte, the medium will turn bright red. If the fungus is not a dermatophyte, no color change will be noted. If kept beyond 14 days, false positive can result even with non-dermatophytes. Specimen from the DTM can be sent for species identification if desired.
Often dermatophyte infection may resemble other inflammatory skin disorders or dermatitis, thus leading to misdiagnosis of fungal infections.
While even healthy individuals may become infected, there is an increased susceptibility to infection when there is a preexisting injury to the skin such as scars, burns, excessive temperature and humidity. Adaptation to growth on humans by most geophilic species resulted in diminished loss of sporulation, sexuality, and other soil-associated characteristics.
The mixture of species is quite different in domesticated animals and pets (see ringworm for details).
Infections occur more in males than in females, as the predominantly female hormone, progesterone, inhibits the growth of dermatophyte fungi.
For extensive skin lesions, itraconazole and terbinafine can speed up healing. Terbinafine is preferred over itraconazole due to fewer drug interactions.
Tinea unguium (nails) usually will require oral treatment with terbinafine, itraconazole, or griseofulvin. Griseofulvin is usually not as effective as terbinafine or itraconazole. A lacquer (Penlac) can be used daily, but is ineffective unless combined with aggressive debridement of the affected nail.
Tinea capitis (scalp) must be treated orally, as the medication must be present deep in the hair follicles to eradicate the fungus. Usually griseofulvin is given orally for 2 to 3 months. Clinically dosage up to twice the recommended dose might be used due to relative resistance of some strains of dermatophytes.
Tinea pedis is usually treated with topical medicines, like ketoconazole or terbinafine, and pills, or with medicines that contains miconazole, clotrimazole, or tolnaftate. Antibiotics may be necessary to treat secondary bacterial infections that occur in addition to the fungus (for example, from scratching).
Tinea cruris (groin) should be kept dry as much as possible.
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