Protruding nipples in boys may be a physiological reaction, or it may be caused by pathological reasons such as breast hyperplasia and nipple allergy. 1. Physiological reaction: If nipple protrusion is caused by cold or shock, it is a normal physiological reaction and the symptoms will disappear after removing the stimulating factors. 2. Mammary gland hyperplasia: after taking estrogen, men may cause endocrine disorders, which will result in symptoms such as hard lumps in breasts, enlarged nipples, and bulging, etc. Protruding nipples in boys may be caused by mammary gland hyperplasia. 3. Nipple allergy: after contact with allergens, it will stimulate the capillaries of the skin, making the capillaries congested, which will lead to swelling, boy breast protrusion may be caused by nipple contact with allergens. Boys protruding mammary glands may also be seen in breast fibers, cysts and other diseases, if the symptoms of boys protruding mammary glands, persistent and unrelieved, you need to seek timely medical treatment.