A number of infectious agents and infection-related conditions can contribute to hair loss. Some common ones are described here.
Surprisingly, ringworm has nothing to do with worms, but is a fungal infection that can occur anywhere on the body. If it develops on the scalp, it can cause patches of hair loss and is known to doctors as "tinea capitis." Ringworm is the same thing as athlete's foot, and the same kind of fungal infection that can affect the nails too.
On the scalp, ringworm usually begins as a small pimple that progressively expands in size, leaving scaly patches of temporary baldness. The fungus gets into the hair fibers in the affected area and these hairs become brittle and break off easily, leaving a bald patch of skin. Affected areas are often itchy, red, and inflamed, with scaly patches that may blister and ooze. The patches are usually redder around the outside with a more normal skin tone in the center. This may create the appearance of a ring -- hence the name, ringworm.
Worldwide, the fungus Microsporum audouinii is a very common cause of ringworm, but increasingly Trichophyton tonsurans can also cause tinea capitis, especially in the US and Latin American countries. Other fungi that may cause tinea capitis include Trichophyton schoenleinii and Trichophyton megninii in Southern Europe and Africa, and Trichophyton violaceum in the Middle East.
The fungus Microsporum gypseum can also sometimes cause tinea capitis. This fungus is common in soil and may be transferred to humans by contact with infected animals. You can also get ringworm from pets that carry the fungus, and cats in particular are common carriers. Ringworm is contagious. It can be passed from one person to the next by direct skin-to-skin contact. You can also catch ringworm through contact with contaminated items such as combs, unwashed clothing, and shower or pool surfaces.
Treatment for ringworm varies depending on the particular fungus involved. Some types of ringworm infection will go away spontaneously and no treatment is given. However, most commonly, griseofulvin, an anti-fungal, is used. Griseofulvin is very effective against fungi in hair and skin but it is not so good at treating yeast or bacterial infections. The drug gradually accumulates in the skin and hair. It especially likes to bind with keratin, which is a key component of hair, skin, and nails, and blocks the fungus from infecting the keratin.
More recently, some fungi that cause tinea capitis show some resistance to the drug, which means higher doses and longer courses of treatment. As an alternative to griseofulvin, newer anti-fungal drugs like terbinafine, itraconazole, and fluconazole can be prescribed.