Polymastia, also called hypermastia or accessory breast tissue, is commonly found in the axillary (the armpit or a corresponding part). In women who suffer from this condition, swelling and tenderness in the armpit are common during puberty, menstruation, or after delivery.
The armpit can also become engorged and painful, especially for women, after delivery. There is no visible nipple or areola in most cases, but in other cases where there are working ducts, leaking of milk from the armpit can be expected.
An affected individual may not even realise the presence of axillary breast tissue. Because it is similar to normal breast tissue, it is only discovered during the first occurrence of menstruation, pregnancy or lactation.