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|Classification and external resources|
Characteristic "bull's eye" rash (erythema migrans) of early Lyme disease
Erythema (from the Greek erythros, meaning red) is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation. Examples of erythema not associated with pathology include nervous blushes.
Erythema disappears on finger pressure (blanching), while purpura or bleeding in the skin and pigmentation do not. There is no temperature elevation in erythema, unless it is associated with the dilation of arteries in the deeper layer of the skin.
It can be caused by infection, massage, electrical treatment, acne medication, allergies, exercise, solar radiation (sunburn), cutaneous radiation syndrome, niacin administration, or waxing and tweezing of the hairs—any of which can cause the capillaries to dilate, resulting in redness. Erythema is a common side effect of radiotherapy treatment due to patient exposure to ionizing radiation.
In about 30–50% of cases, the cause of erythema is unknown.
May also be caused by Vitamin A toxicity.
Associated conditions 
- Erythema ab igne
- Erythema chronicum migrans
- Erythema induratum
- Erythema infectiosum (or fifth disease)
- Erythema marginatum
- Erythema migrans
- Erythema multiforme (EM)
- Erythema nodosum
- Erythema toxicum
- Keratolytic winter erythema
- Palmar erythema
See also 
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