Abnormal skin redness from increased blood flow, caused by dilation and irritation of surface capillaries. It has a variety of manifestations. In erythema multiforme, a symptom complex seen in several diseases, spots appear suddenly, often with a bull's-eye pattern. It may become life-threatening in severe cases; in mild cases symptoms may recur. Hormone treatment may be effective. In erythema nodosum, a hypersensitivity reaction usually associated with strep infection (see streptococcus), drugs, or the disease sarcoidosis, painful red nodules appear in the deeper skin layer of the lower legs. They usually disappear over several weeks and do not recur. Another form of erythema is pellagra.
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In about 30-50% of cases, the cause of Erythema is unknown.