Thrush, or oropharyngeal candidiasis, is an infection of the mouth and throat caused by the fungus Candida, a genus of yeast. This microorganism is naturally present on the skin and mucous membranes, but overgrowth can cause disease. Candidiasis is not considered communicable because the microorganism is ubiquitous (common and widespread).

Symptoms of thrush include cottage cheese-like white patches in the mouth and throat, with raw areas underneath. Esophageal involvement may result in difficulty in swallowing, nausea, vomiting, and chest pain. Candidiasis is confirmed by culture from a swab of the infected tissue.

Proliferation of Candida is most often the result of a weakened immune system. Candidiasis is one of the most common and visible opportunistic infections that strike people with AIDS, chemotherapy patients, and other immunocompromised individuals. Many AIDS patients have been first diagnosed after they, or their dentists, noticed a thrush infection. In individuals with normal immune systems, candidiasis may be associated with antibiotic use. Infants, diabetics, smokers, and denture wearers are particularly susceptible to thrush.

In addition to causing thrush, Candida may affect the gastrointestinal tract or genitals. The microorganism may also enter the bloodstream, either via surgery or catheterization, or through damage to the skin or mucosa. If the immune system is unable to clear the fungus from the bloodstream, a dangerous systemic infection may occur, resulting in endocarditis, meningitis, or other serious problems.

Antifungal medications such as fluconazole and clotrimazole are generally effective in treating candidiasis. However, drug-resistant strains of Candida are becoming increasingly prevalent, and recurrence is common. This situation is driving research into new therapies and potential vaccines.