Fungi are plant-like organisms that may cause infection. Many different types of fungi can affect the skin. Some are naturally present in the human body and are called yeast. Others are foreign particles that cause infection when they grow on the human body and are called dermatophytes.

Fungi grow best in areas that are warm, moist and dark. Therefore, they thrive in tropical environments. In humans, fungi grow well on skin, in skin folds (e.g., breast folds, groin, armpits) or in mucous membranes (e.g., mouth, genitals).

The most common type of yeast infection is candidiasis. Common candidiasis infections include thrush (yeast infection of the mouth) and yeast onychomycosis (yeast infection of the nails). Some common dermatophyte infections include athlete’s foot and ringworm (round red patches with scales on the edges).

Symptoms of fungal infection vary depending on the type of infection present, but may include skin rash and itching (pruritus). Yeast infections may occur when the immune system is weakened, such as by illness, stress or certain medications. Dermatophyte infections may spread due to contact with infected humans or animals or contaminated objects or soil.

Fungal skin infections are diagnosed by physical examination, skin scrapings and examination of skin scrapings under a microscope, and fungal cultures. Occasionally a biopsy of the involved area is performed as well. 

Topical antifungal medications, which are applied directly to the skin, are typically the first-line treatment for fungal skin infections. Resistant or chronic infections (e.g., athlete’s foot) may require oral antifungal medications.

Fungal skin infections can usually be prevented by maintaining proper hygiene. It is important to keep the skin clean and dry, to wear clean clothing every day and to avoid using other people’s personal items (e.g., towels, toiletries).