Breast development in males (gynaecomastia) is most usually an over enthusiastic response during puberty.
The male and female breast is identical before puberty. At puberty some degree of breast development in men is normal, and just as some women have very little and others have very significant breast development, so too some men develop significantly as their normal response during puberty.
There are other reasons for breast development in males, including hormonal imbalances, and as a response to some medications, including anabolic steroids, and it must be remembered that 1% of all breast cancer occurs in males: therefore it is important to have any unusual breast development examined by your doctor.
Treatment depends on whether the breast development is mainly fatty, in which case liposuction can produce excellent results, or mainly glandular, in which case surgical excision is required. Often a combination of surgery and liposuction is required and in many cases liposuction in combination with avulsion of the glandular component is effective with minimal scars.