Noma is a disorder that causes sudden, rapidly progressive tissue destruction. The mucous membranes (e.g., gums, lining of the cheeks) become inflamed and develop ulcers. The infection spreads from the mucous membranes to the skin. The tissues in the lips and cheeks die. Rapid, painless tissue breakdown continues and this gangrenous process can destroy the soft tissue and bone. Noma can also affect the mucous membranes of the genitals, spreading to the genital skin (this is sometimes called noma pudendi).

This disorder occurs primarily in young, severely malnourished children 2-5 years of age. Often they have had a preceding illness such as measles, scarlet fever, tuberculosis, malignancy, or immunodeficiency. It is seen in areas of poor cleanliness and sanitation. The exact cause is unknown, but may be bacterial (fusospirochetal organisms).

Risk factors include Kwashiorkor and other forms of severe protein malnutrition, poor sanitation and poor cleanliness, disorders such as measles or leukemia, and living in an underdeveloped country.