Dermatophytosis, also known as ringworm, is a fungal infection of the skin. Typically it results in a red, itchy, scaly, circular rash. Hair loss may occur in the area affected. Symptoms begin four to fourteen days after exposure. Multiple areas can be affected at a given time.

About 40 types of fungus can cause ringworm. They are typically of the Trichophyton, Microsporum, or Epidermophyton type. Risk factors include using public showers, contact sports such as wrestling, excessive sweating, contact with animals, obesity, and poor immune function. Ringworm can spread from other animals or between people. Diagnosis is often based on the appearance and symptoms. It may be confirmed by either culturing or looking at a skin scraping under a microscope.

Prevention is by keeping the skin dry, not walking barefoot in public, and not sharing personal items. Treatment is typically with antifungal creams such as clotrimazole or miconazole. If the scalp is involved, antifungals by mouth such as fluconazole may be needed.

Globally, up to 20% of the population may be infected by ringworm at any given time. Infections of the groin are more common in males, while infections of the scalp and body occur equally in both sexes. Infections of the scalp are most common in children while infections of the groin are most common in the elderly. Descriptions of ringworm date back to ancient history.