Cause

Ringworm infection is caused by a fungus. Fungi (plural of fungus) that cause ringworm live and spread on the outer layer of skin. Ringworm is not caused by a worm or other parasite.

Fungi are present everywhere in our environment, including on the human body. They thrive in warm, moist areas, such as locker rooms and swimming pools, and in skin folds. You can get ringworm of the skin by sharing contaminated towels, clothing, and sports equipment, and by direct contact with an infected person.

Ringworm of the skin (tinea corporis) is most commonly caused by the fungus Trichophyton rubrum, which spreads from one person to another. It can also be caused by Microsporum canis, which is spread by cats and dogs. This type is less common but causes a more severe infection.

People often get ringworm of the groin ("jock itch") by accidentally spreading athlete's foot fungus to their own groin area. People with athlete's foot also commonly spread it to their hands (tinea manuum).

Some people are more likely to get (susceptible to) fungal infections than others. The tendency to get fungal skin infections or to have them return after treatment seems to run in families.

Symptoms

Most ringworm infections cause a rash that may be peeling, cracking, scaling, itching, and red. Sometimes the rash forms blisters, especially on the feet. See a picture of a typical ringworm skin rash.

Symptoms of ringworm of the body include a rash:

• On the chest, stomach, arms, legs, or back.
• With edges that are red and scaly or moist and crusted. The rash also may have small bumps that look like blisters. The center of the rash may be clear, giving it a ring-shaped appearance, or there may be a cluster of red bumps.
• That may forms large, round patches.

Symptoms of ringworm of the face include a rash:

• On the face, the ears, or both.
• With a border that may not be very distinct.
• That may get worse after being in the sun.

Symptoms of ringworm of the groin (jock itch) include a rash:

• On the groin, skin folds, inner thighs, or buttocks. The rash usually does not occur on the scrotum or penis.
• With edges that are very distinct and may be scaly or have bumps that look like blisters.
• That may have a red-brown center.

Jock itch and athlete's foot frequently occur at the same time.

Symptoms of ringworm on the hand include a rash:

• On the palm that may be mistaken for eczema.
• On the palm that is thickened, dry, and scaly, similar to athlete's foot, while skin between the fingers may be moist and have open sores.
• On the back of the hand that is red and scaly, with edges that have bumps that look like blisters.

Fingernails can also be infected. For more information, see the topic Fungal Nail Infections.

Ringworm of the skin may be confused with other conditions with similar symptoms, such as eczema or psoriasis.