There are any number of underlying causes for gynecomastia including a hormone imbalance, certain medical conditions and drug use. But the most common reason is that you simply have a genetic tendency towards gynecomastia. This is part of what makes it so frustrating. You want to understand why it happened or if you were to blame. In most cases, there is nothing that you can do or could have done to prevent your gynecomastia. Thankfully, the treatment options are very effective and totally life changing.