[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Molds and dermatophytes](https://durgical.com/en/microbiology/groups/molds-and-dermatophytes/) › Dermatophytes (Trichophyton, Microsporum, Epidermophyton)

[Microbiology](https://durgical.com/en/microbiology/) · [Molds and dermatophytes](https://durgical.com/en/microbiology/groups/molds-and-dermatophytes/)

# Dermatophytes (Trichophyton, Microsporum, Epidermophyton)

- Fungus
- Exam priority: medium

Fungi that feed on keratin and cause tinea of the skin, scalp, groin, feet and nails. Spread by contact with people, animals or objects.

Updated 2026-11-01

Also called: ringworm, tinea, athlete's foot, nail fungus

## Key points

- Three genera: Trichophyton (skin, hair, nail), Microsporum (skin, hair), Epidermophyton (skin, nail)
- KOH: septate hyphae
- Tinea capitis needs oral treatment
- T. rubrum is the most common in adults; M. canis comes from cats and dogs
- Topical steroid on tinea: worsens and disguises it

## At a glance

**Shape**
Septate hyphae and arthroconidia in scale, hair or nail

**Family**
Arthrodermataceae (Onygenales)

**Type**
Keratinophilic molds (do not invade living tissue)

**Stain**
KOH: branching septate hyphae; Wood's lamp: some Microsporum species fluoresce

**Size**
Hyphae about 2–4 µm wide

## Morphology

- In scale on KOH: septate hyphae that branch and break into arthroconidia
- Trichophyton: many microconidia; Microsporum: large rough-walled macroconidia; Epidermophyton: club-shaped macroconidia, no microconidia
- In hair they can invade inside the shaft (endothrix) or outside it (ectothrix)

## Transmission

- Direct skin contact with infected people (anthropophilic, such as T. rubrum)
- Contact with animals, mainly cats and dogs (zoophilic, such as M. canis)
- Contact with soil (geophilic)
- Shared objects and wet floors: towels, combs, showers, pools

**Reservoir:** Humans; Cats, dogs and livestock; Soil

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Keratinases that digest keratin
- Grow in the stratum corneum, hair and nail; tolerate deep body temperature poorly
- Inflammation is stronger with animal or soil species

## Diseases it causes

- Dermatophytosis (tinea): tinea corporis, capitis, cruris, pedis and onychomycosis (tinea unguium) [Dermatophytosis (tinea) and onychomycosis →](https://durgical.com/en/conditions/dermatophytosis-and-onychomycosis/)

## Clinical picture

- Tinea corporis: annular plaque with a scaly active border and clearer centre
- Tinea capitis in children: patches with broken hairs and scaling; kerion is an inflammatory form
- Tinea pedis: scaling and cracks between the toes
- Onychomycosis: thick, yellow, brittle nail, mostly toenails
- Tinea incognito: atypical look after steroid creams

## Diagnosis

- KOH direct exam of scale, hair or nail
- Culture on Sabouraud (or dermatophyte medium) for the species
- Wood's lamp: green fluorescence in some Microsporum tinea
- Biopsy with PAS in doubtful onychomycosis

## Treatment

Skin tinea: topical antifungals (azoles such as clotrimazole or allylamines such as terbinafine). Scalp tinea and onychomycosis: oral treatment (terbinafine, griseofulvin, itraconazole). Terbinafine-resistant strains (such as T. indotineae) have emerged; steroid creams make tinea worse.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Terbinafine](https://durgical.com/en/pharmacology/terbinafine/)
- [Griseofulvin](https://durgical.com/en/pharmacology/griseofulvin/)
- [Clotrimazole](https://durgical.com/en/pharmacology/clotrimazole/)
- [Itraconazole](https://durgical.com/en/pharmacology/itraconazole/)

## Prevention

- Dry feet and skin folds well; footwear in showers and pools
- Do not share towels, combs or caps
- Treat pets with lesions
- Confirm the diagnosis before treating, to avoid needless steroids and antifungals

## Memory aid

Tri, Micro, Epi: skin for all; hair for Tri and Micro; nails for Tri and Epi. Epi never touches hair.

## Test yourself

Think of the answer, then tap the question to see it.

## Which quick office test confirms tinea?

A KOH direct exam of scale, hair or nail, showing septate hyphae.

## Which dermatophyte does not affect hair?

Epidermophyton (it affects skin and nails).

## Why is tinea capitis not treated with creams alone?

The fungus sits inside the follicle and hair shaft, where cream does not reach; it needs an oral antifungal.

## What happens if a steroid cream is put on tinea?

The infection worsens and changes its look (tinea incognito), which makes diagnosis harder.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/dermatophytes/)

## Related

- [Malassezia](https://durgical.com/en/microbiology/malassezia/)
- [Candida albicans](https://durgical.com/en/microbiology/candida-albicans/)

## Related conditions

- [Dermatophytosis (tinea) and onychomycosis](https://durgical.com/en/conditions/dermatophytosis-and-onychomycosis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Molds and dermatophytes](https://durgical.com/en/microbiology/groups/molds-and-dermatophytes/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Ringworm Basics](https://www.cdc.gov/ringworm/about/index.html) (CDC, 2024); [Clinical Overview of Ringworm](https://www.cdc.gov/ringworm/hcp/clinical-overview/index.html) (CDC, 2024); [Ringworm: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001439.htm) (MedlinePlus (NLM), 2024).

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Representative model, for educational purposes only.

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