Ringworm is a superficial fungal infection of the skin, nails, or hair. The causative agent is not a worm, but a type of mold called a dermatophyte (“skin plant”). Dermatophytes love non-living and/or keratinized tissue, like the stratum corneum of the skin, the nails, and the hair. There are three genera, if you care: microsporum, trichophyton, and epidermophyton.

Most of the time, the dermatophytoses (a more official name than ringworm) are classified by their location. The word “tinea” (meaning, in this case, “dermatophytosis”) usually precedes the anatomic location. Here are some common dermatophytoses:

Tinea capitis (dermatophytosis involving the scalp)
Tinea barbae (dermatophytosis involving the beard area)
Tinea pedis (dermatophytosis involving the feet, commonly called “athlete’s foot”)
Tinea crurus (dermatophytosis involving the groin, commonly called “jock itch”)
Tinea corporis (dermatophytosis involving skin in any other anatomic location)
Tinea unguium (dermatophytosis involving the nails)

There are a couple unique kinds of dermatophytoses too, including tinea nigra (a tropical condition in which dark brown fungi cause brown/black macules on palms or soles) and piedra (a fungal infection of the hair shaft itself).

Dermatophytoses affecting the skin have a characteristic ring-shaped lesion with a raised, red, sharply-demarcated border. This is probably where the worm idea came in – people thought the advancing borders of the lesion indicated the presence of a worm in the skin. These lesions are most common in warm, moist areas of the body, but they can occur anywhere, really. They are not dangerous – just bothersome.

Note: the nice picture of an athlete’s foot (perhaps with a ringworm infection between the first and second toes) was taken in the Capitolene Museum in Rome by Thrillho. It can be found at: