In short. The three groups of fungi that infect skin, hair and nails, where each lives, and why the distinction decides which treatment works.
Key points
- Dermatophytes live only in dead keratin: skin surface, hair shafts and nail plates.
- Malassezia lives in the oily, sebum-rich skin of the trunk, scalp and upper back.
- Candida lives on mucous membranes and in moist skin folds.
Fungi are not a single enemy. The organisms that infect human skin fall into three practical groups, and knowing which group is involved explains almost everything about how an infection behaves, how long it lasts, and what will treat it.
Dermatophytes
Dermatophytes are moulds that digest keratin — the protein in the dead outer layer of skin, in hair and in nails. They cannot invade living tissue, which is why they stay in the surface layer, the hair shaft and the nail plate. They cause ringworm of the body and groin, athlete's foot, scalp ringworm and most nail fungus. They are acquired from other people, from animals such as cats, dogs and cattle, and from soil. Because they live only in keratin, a topical antifungal can reach them in the skin — but not inside a nail plate or a hair follicle, which is why those sites need oral treatment.
Yeasts
Yeasts are single-celled fungi. The one that lives on human skin, Malassezia, is present on almost everyone and normally causes no trouble. It causes pityriasis versicolor when it overgrows, and contributes to seborrhoeic dermatitis. Candida species live in the gut and on mucous membranes and cause skin infection mainly in warm, moist, occluded folds, and in people who are diabetic, obese, or taking antibiotics or immunosuppressive treatment. Yeast infections do not come from animals and are not caught from soil.
Moulds and the environment
Environmental moulds occasionally infect skin, almost always after trauma in someone immunosuppressed, and they are a different and more serious problem. In healthy people, the great majority of fungal skin disease is dermatophyte or yeast.
Where each group lives
Dermatophytes live only in dead keratin: skin surface, hair shafts and nail plates. Malassezia lives in the oily, sebum-rich skin of the trunk, scalp and upper back. Candida lives on mucous membranes and in moist skin folds. That map predicts where each infection appears and which treatment can reach it.
Why the distinction matters in practice
Dermatophyte infection of the skin usually responds to a topical antifungal given for weeks, not days. The same organism inside a nail needs oral treatment for months. Pityriasis versicolor needs a different approach again, and it leaves pale or brown patches that persist long after the fungus has gone. Candidal infection in a fold improves only when the moisture, friction and any underlying diabetes are addressed as well as the fungus. Treating all three as one condition is how patients end up with drawers full of creams that never worked. Confirmation is straightforward and worth doing: microscopy of a scraping takes minutes and separates fungal infection from the many rashes that imitate it.
Get the rash looked at if
- It has been treated as fungal infection for several weeks and is not settling.
- The scalp, beard or nails are involved — these sites usually need oral treatment.
- You have diabetes, HIV, or take immunosuppressive treatment and the rash is spreading.
Frequently asked questions
Why can a cream clear ringworm on the skin but not the same fungus in a nail?
Dermatophytes live only in dead keratin, so a topical antifungal can reach them in the skin surface layer. It cannot reach inside a nail plate or a hair follicle, which is why infection at those sites usually needs oral treatment.
Which fungal skin infections are caught from animals or soil?
Dermatophytes are acquired from other people, from animals such as cats, dogs and cattle, and from soil. Malassezia lives on almost everyone and is not caught from anyone, and Candida lives on mucous membranes and in the gut rather than coming from animals or soil.
Why does a candidal rash in a skin fold return so often?
Moisture, friction, occlusion, diabetes, obesity and antibiotic treatment all create the conditions Candida needs. A fold infection improves only when those factors are addressed as well as the fungus, so the rash returns promptly when only the yeast is treated.
Risks & Limitations
- Treatment fails if the diagnosis is wrong, or if the course is shorter than the infection requires.
- Relapse after apparent cure is common — reinfection from feet, nails, pets, household contacts or shared floors.
- Oral antifungals interact with many common medicines and need liver and blood monitoring.
- Skin colour change and scarring can follow infection, and may take months to fade or be permanent.
- Warts recur after any treatment, and no single treatment is guaranteed to clear them.
- Antiviral treatment for herpes works best started early, and it does not remove the virus.
- Nail fungus treatment takes months, and a proportion of people relapse afterwards.
When to Seek Care
- Fever with a spreading rash, or pain far worse than the skin appears — seek emergency care the same day.
- Rapidly spreading redness, swelling, dusky or blistered skin, or numbness over the area.
- Shingles near the eye or on the tip of the nose, or eye pain, redness or blurred vision.
- Blistering skin, or a rash involving the eyes, mouth or genitals.
- Any skin infection with fever in someone who is immunocompromised, diabetic, or taking steroids or chemotherapy.
References & Further Reading
- American Academy of Dermatology (AAD) — public and clinical guidance
- World Health Organization (WHO) — skin and infectious disease resources
- Centers for Disease Control and Prevention (CDC) — infection prevention and treatment guidance
- Chinese Medical Association, Dermatology Branch — clinical guidance
- Cochrane Library — systematic reviews in skin infection and dermatology
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.