Red, swollen and painful nipples can be caused by wear and tear of clothing, trauma and mastitis. 1. Clothing wear: when patients wear poor quality underwear for a long time, it may cause prolonged wear and tear to the nipple area, resulting in redness, swelling and pain in the area, which may also be accompanied by a certain burning sensation. 2. Trauma: When the nipple area is damaged by direct or indirect violence from outside, it may lead to soft tissue damage, causing nipple redness, swelling and pain, and some patients may also have nipple bleeding. 3. Mastitis: Mastitis can be induced by bacterial growth in the mammary gland, and the inflammation can cause repeated stimulation of the nipple area, which can also cause redness, swelling and pain. Red, swollen and painful nipples can also be caused by other reasons such as inflammatory breast cancer, so patients should go to the hospital in time and take appropriate treatment.