Fungal Infection of the Skin

What causes fungal skin infections

Three groups of fungi cause most skin infections:

• Dermatophytes (Trichophyton, Microsporum, Epidermophyton): feed on keratin, the protein in skin, hair and nails. They cause the "tinea" infections and are contagious.
• Yeasts (Candida): live harmlessly on skin and in the gut but overgrow in warm, wet, rubbing skin folds.
• Malassezia: a yeast on everyone's skin that causes tinea versicolor and contributes to seborrheic dermatitis.

Fungi thrive where skin stays warm and damp: feet in closed shoes, the groin, under the breasts, belly folds and armpits.

Types of fungal skin infection by body area

Symptoms

• Itching, often the main complaint
• Redness (or darker brown or purple patches on brown and black skin)
• Scaling, peeling or cracking
• A ring shape with a more active edge
• Soreness or burning in moist areas, typical of candida
• Small blisters at the edge, especially on the feet

Who is at risk

• Sweating heavily, wearing tight clothing or closed shoes for long periods
• Communal showers, pools and locker rooms; contact sports such as wrestling (tinea gladiatorum)
• Close contact with an infected person or pet, especially cats, dogs and guinea pigs
• Diabetes, obesity and a weakened immune system
• Antibiotic or steroid use, which raises the risk of candida
• Young children (scalp ringworm) and older adults (nail fungus)

How to tell if a rash is fungal

Fungal rashes are often confused with eczema and psoriasis. Clues that point toward fungus:

• one side of the body or one area, spreading slowly outward
• a clearly defined, scaly, active edge with a clearer center
• a rash that gets worse after using a steroid cream alone
• itchy, peeling skin between the toes alongside the rash

Eczema is usually symmetrical, in skin creases, with ill-defined edges and very dry skin. Psoriasis forms thick, silvery plaques on elbows, knees and scalp.

A doctor can confirm a fungal infection by scraping some scale and looking at it under a microscope with potassium hydroxide (KOH test), or by sending it for culture. A Wood's lamp (ultraviolet light) makes some scalp infections and tinea versicolor glow.

Treatment

Over-the-counter antifungal creams

• Terbinafine and butenafine creams work fastest for tinea, often in 1 to 2 weeks.
• Clotrimazole and miconazole creams treat both tinea and candida, usually used for 2 to 4 weeks.
• Apply to the rash and about 2 cm (1 in) of normal skin around it, once or twice a day.
• Keep going for 1 to 2 weeks after the skin looks clear, or the infection often returns.

For tinea versicolor, selenium sulfide or ketoconazole shampoo used as a body wash is effective. Skin color takes months to even out after the fungus is gone.

Prescription treatment

• Antifungal tablets (such as terbinafine, itraconazole, fluconazole or griseofulvin) are needed for scalp ringworm, nail infections, widespread or stubborn tinea, and severe infections in people with weak immune systems. Some require blood tests for liver function.
• Medicated nail lacquers help mild nail infections but take a year or more.

Antifungal resistance is growing. Strains such as Trichophyton indotineae cause widespread, stubborn infections that do not respond to terbinafine. See a dermatologist if a rash keeps returning despite correct treatment.

Preventing fungal skin infections

• Dry thoroughly after washing, especially between the toes and in skin folds.
• Change socks and underwear daily, and choose breathable fabrics.
• Wear sandals in communal showers and pool areas.
• Do not share towels, razors, combs or shoes.
• Alternate shoes so each pair dries out for 24 hours.
• Have pets with patchy hair loss checked by a vet.
• Put socks on before underwear if you have athlete's foot, to avoid spreading it to the groin.

Frequently asked questions

What does a fungal skin infection look like?

Usually an itchy, red or darker patch with fine scale. Tinea often forms a ring with a raised, scaly edge and clearer middle. Candida in skin folds is bright red, moist and sore with small spots around the edge. Tinea versicolor causes pale or brown patches on the chest and back.

How long does a fungal skin infection take to go away?

With an antifungal cream, most skin infections improve within 1 to 2 weeks and clear in 2 to 4 weeks. Keep applying for 1 to 2 weeks after the skin looks normal. Scalp infections need 6 to 8 weeks of tablets, and nail infections take months.

Is a fungal skin infection contagious?

Tinea infections are contagious through skin contact, shared towels, floors and pets. Candida and tinea versicolor come from fungi already on your skin and rarely spread to others. Cover the rash and wash hands after touching it to protect others.

Can I use hydrocortisone on a fungal rash?

It is best not to. Hydrocortisone can reduce itching briefly but lets the fungus spread and makes the rash harder to diagnose. Use an antifungal cream instead, and see a doctor if you are unsure whether the rash is fungal.

Why does my fungal infection keep coming back?

Common reasons are stopping treatment too early, untreated athlete's foot or nail fungus reseeding the infection, damp shoes, infected pets or family members, and conditions such as diabetes. Treat every site at the same time and keep skin dry.