It can be caused by infection, massage, electrical treatments, acne medication, allergies, exercise, solar radiation (sunburn), or waxing and plucking 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.
