- Erythema (from the Greek erythros, meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation.
- Erythema nodosum is a type of skin inflammation that is located in a part of the fatty layer of skin. Erythema nodosum results in reddish, painful, tender lumps most commonly located in the front of the legs below the knees. The tender lumps, or nodules, of erythema nodosum range in size from a dime to a quarter. It usually occurs symmetrically on the lateral side of the lower legs and occasionally on the medial side of the lower legs and buttocks. The onset is usually abrupt. The course of the disease is usually about six weeks but may last several months.
- Erythema induratum is a panniculitis on the calves. It occurs mainly in women, but it is very rare now. Historically, when it has occurred, it has often been concomitant with cutaneous tuberculosis, and it was formerly thought to be always a reaction to the tuberculum bacillus.
- Erythema multiforme (EM) is a skin condition of unknown cause; it is a type of erythema possibly mediated by deposition of immune complexes (mostly IgM-bound complexes) in the superficial microvasculature of the skin and oral mucous membrane that usually follows an infection or drug exposure. It is an uncommon disorder, with peak incidence in the second and third decades of life. The disorder has various forms or presentations, which its name reflects (multiforme, "multiform"). Target lesions are a typical manifestation. Two types, one mild to moderate and one severe, are recognized (erythema multiforme minor and erythema multiforme major). The disease mostly affects females. The lesion often appears symmetrically on the dorsum of the hand, palms, finger edges,insteps, heels,face, neck, mucous membranes of the mouth and genitalia. The patient has a feeling of burning Heat and itching. The course is usually two to three weeks, but is liable to relapse.