Cause
Ringworm infection is caused by a fungus. Fungi that cause ringworm live and multiply on the upper layer of the skin and on the hair. Ringworm is not caused by a worm or other parasite.
The medical term for fungal infections is tinea, followed by a word that describes the location of infection. For example, tinea capitis is ringworm of the scalp, and tinea barbae is ringworm of the beard.
Ringworm of the scalp is most commonly caused by the fungus Trichophyton tonsurans, which is spread from one person to another. This fungus causes more than 90 out of every 100 cases of ringworm of the scalp in North and Central America.1 In the past, the fungus Microsporum canis was the most common cause, but it is a less frequent cause now. Microsporum canis is spread by cats and dogs.
Ringworm of the beard is caused by Trichophyton verrucosum and is spread by cattle and other farm animals.
You can catch ringworm by sharing contaminated hats, combs, brushes, towels, telephones, clothing, sports equipment, or even theater seats, and by direct contact with an infected person.
Children are more susceptible to the fungus and more likely to develop an infection than adults. Adults often do not develop an infection even after exposure to ringworm-causing fungi. Adults, and less commonly children, can be carriers for ringworm—carriers can pass ringworm on to others but do not have symptoms of the disease.
Ringworm-causing fungi can live on people, objects (such as hats or brushes), or animals for several months.
