There are many causes of nipple pain in men, such as: 1. Pain caused by trauma or friction. Excessive exercise when clothing friction leads to nipple injury, sometimes with nipple rupture bleeding and other symptoms, you can use band-aids or apply ointment treatment. The nipples are bumped causing pain and redness, you can ice first, and then apply hot compresses after 48 hours. 2, allergies. The nipple contact with allergens appear red, swollen, painful, and itchy, you can actively anti-allergy treatment, check and away from allergens. 3, breast disease. Men who have abnormal hormone levels in their bodies can also have breast diseases, such as mastopexy and breast cancer. They should not abuse estrogen and eat less soy products with high estrogen content. Maintain good living habits, overcome psychological barriers, and actively go to the hospital for treatment, either with medication or surgery if necessary.