Gynecomastia is the most common type of benign breast disease in males. It is general swelling of breast tissue, usually caused by increased estrogen hormone levels in the body. Estrogens may be in medications, foods or dietary supplements. Gynecomastia usually occurs in males in their thirties. Adolescents and older males can also develop gynecomastia.

Other less common types of male breast disease include fibroadenoma or juvenile fibroadenoma. These conditions usually occur in younger men.

Estrogen stimulation, a benign tumor, or medication can cause a breast nipple discharge in males.

Infection of the breast tissue, called mastitis, is common in females. It can occur due to a local skin injury, such as a bruise or insect sting. The skin around the breast area can become infected and cause an abscess or cellulitis. Mastitis is rare in males.