Unilateral breast tenderness is especially obvious, which may be related to thinner, enlarged breast, mastitis, breast hyperplasia, breast cancer and other conditions. 1. Thinness: If the patient is thin, the subcutaneous fat content is low, the skin in the breast area is thin, and superficial blood vessels can be seen vaguely, so the veins are particularly obvious. 2. Breast enlargement: If a woman is in the late stage of pregnancy or breastfeeding, due to the influence of estrogen and progesterone, it will lead to rapid enlargement of the breast, and the capillaries of the chest wall will increase and expand and become congested, resulting in venous vasodilatation. 3. Mastitis: If a woman has mastitis, it can lead to breast enlargement, redness, swelling and pain, as well as bruising and other symptoms. 4. Mammal hyperplasia: During the onset of mastal hyperplasia, the proliferation of breast glands may lead to the appearance of lumps or nodules in the breasts, affecting the normal blood flow and leading to the appearance of bruises. 5. Breast cancer: If the patient has breast cancer, there may be symptoms such as dilated veins in the chest wall, nipple blood overflow, lumps inside the breast, and cellulite-like changes in the breast. Unilateral breast bruising is especially obvious may also be other reasons, should promptly consult a doctor, do a systematic examination and diagnosis, and actively deal with.