ERYTHEMA

Erythema is skin redness that is symptomatic of such disorders as allergy, histoplasmosis, and rheumatic fever; sarcoidosis, coccidioidomycosis, rubella (German measles), Mediterranean fever, and ulcerative colitis; as well as a number of more familiar conditions including sunburn, chemical poisoning, sensitivity to certain oral contraceptives, and emotional excitement. Such malignancies as leukemia and lymphoma may also be accompanied by erythema.
Erythema is due to increased amounts of blood in the deeper layers of the skin as a result of the dilation of capillaries. Reddening may be restricted to a small area of the body or may be general over the body surface. The reddened areas turn white when pressed by a finger. In allergy or sunburn erythema disappears within a few days or progresses into some other type of symptom. In such conditions as Mediterranean fever, coccidioidomycosis, histoplasmosis, ulcerative colitis, and sensitivity to oral contraceptives, skin reddening is accompanied by a nodule that is painful to the touch.
Inflammation, in contrast to erythema, includes heat, swelling, and pain as well as redness. Urticaria, or hives, differs from erythema in consisting of raised reddish areas that are similar to pimples or welts.