A chronic superficial slowly spreading skin infection, especially in the folds of the body and webs between the toes, caused by a bacterium called Corynebacterium minutissimum. Erythrasma most often affects adults, especially those with diabetes, and people in the tropics.
Erythrasma looks like a chronic fungal infection. Scaling, cracks, and slight maceration (softening) typically occur in the toe webs, almost always the 3rd and 4th interspaces. Where the thighs contact the scrotum, sharp-edged patches first appear irregular and pink and later become brown with a fine scale. Erythrasma may also involve the armpits, creases below the breasts, abdominal folds, and perineum, particularly in obese middle-aged women or in patients with diabetes mellitus. Erythrasma can be distinguished from ringworm with a Wood's light (a type of UV light) which causes erythrasma characteristically to fluoresce a coral-red color.