Understanding Accessory Breasts: Causes, Symptoms & Treatment Advances in Seoul

“I always thought it was just a stubborn lump under my arm—until I found out it was actually breast tissue,” says a patient treated at Dite Plastic Surgery in Gangnam. For many, the discovery of accessory breast tissue—clinically termed polymastia—can be unexpected and emotionally taxing.

Often overlooked, accessory breasts affect a small percentage of the population and can manifest anywhere along the embryological milk lines—from the armpits to the groin. Though benign, this condition can lead to discomfort, body image concerns, and hormonal sensitivity. With increased awareness and advanced surgical options, individuals now have access to effective, minimally invasive solutions.

What Are Accessory Breasts?

Accessory breasts are extra breast tissue that develops outside the normal pectoral region. Commonly found in the axilla (underarm), this tissue may resemble a soft lump and can even develop areolae or nipples. While typically harmless, their presence may cause physical irritation or psychological distress, particularly during hormonal shifts such as puberty or pregnancy.

The condition, while rare, is not entirely unknown in the medical community. Studies estimate the prevalence of accessory breast tissue to be around 1-6% globally, with a higher incidence in women. However, it can also affect men, often leading to delayed diagnosis due to a lack of awareness. Accessory breasts typically consist of glandular tissue, fat, and sometimes even ductal components, making them biologically similar to normal breast tissue.

What Causes Accessory Breast Tissue?

Accessory breasts form during fetal development when the mammary ridges fail to regress fully. This congenital anomaly can be influenced by several factors: