Fungal infection, also known as mycosis, is a disease caused by fungi. Different types are traditionally divided according to the part of the body affected; superficial, subcutaneous, and systemic. Superficial fungal infections include common tinea of the skin, such as tinea of the body, groin, hands, feet and beard, and yeast infections such as pityriasis versicolor. Subcutaneous types include eumycetoma and chromoblastomycosis, which generally affect tissues in and beneath the skin. Systemic fungal infections are more serious and include cryptococcosis, histoplasmosis, pneumocystis pneumonia, aspergillosis and mucormycosis. Signs and symptoms range widely. There is usually a rash with superficial infection. Fungal infection within the skin or under the skin may present with a lump and skin changes. Pneumonia-like symptoms or meningitis may occur with a deeper or systemic infection.

Fungi are everywhere, but only some cause disease. Fungal infection occurs after spores are either breathed in, come into contact with skin or enter the body through the skin such as via a cut, wound or injection. It is more likely to occur in people with a weak immune system. This includes people with illnesses such as HIV/AIDS, and people taking medicines such as steroids or cancer treatments. Fungi that cause infections in people include yeasts, molds and fungi that are able to exist as both a mold and yeast. The yeast Candida albicans can live in people without producing symptoms, and is able to cause both superficial mild candidiasis in healthy people, such as oral thrush or vaginal yeast infection, and severe systemic candidiasis in those who cannot fight infection themselves.

Diagnosis is generally based on signs and symptoms, microscopy, culture, sometimes requiring a biopsy and the aid of medical imaging. Some superficial fungal infections of the skin can appear similar to other skin conditions such as eczema and lichen planus. Treatment is generally performed using antifungal medicines, usually in the form of a cream or by mouth or injection, depending on the specific infection and its extent. Some require surgically cutting out infected tissue.

Fungal infections have a world-wide distribution and are common, affecting more than one billion people every year. An estimated 1.7 million deaths from fungal disease were reported in 2020. Several, including sporotrichosis, chromoblastomycosis and mycetoma are neglected.

A wide range of fungal infections occur in other animals, and some can be transmitted from animals to people.