The veins on top of the breast are blue, a very common clinical symptom, and the main causes generally include physiological and pathological aspects. Physiologically, the blood vessels are lighter when the skin is fair or the mammary glands and subcutaneous fat are thin. In addition, in women during pregnancy or lactation, the blood vessels on the surface may turn blue, mainly for the secretion of milk or the reaction to pregnancy, physiological changes are related, no special treatment and medication is needed. If it is clear and obvious, it may be a localized mastitis of the breast, or in severe cases, it is not excluded from the possibility of breast hemangioma, which occurs mostly unilaterally. Therefore, it is best to go to a regular hospital for detailed consultation and examination to rule out pathological factors, so that it can be normal and does not require special treatment.