Parastomalacia, also known as polymastia, is a congenital developmental abnormality. In humans, the mammary glands originate from the ectoderm, and during embryonic development, six to eight pairs of mammary primordia are formed at the “breast line” (line from the axilla to the groin). Under normal circumstances, except for the pair of mammary primordia in the anterior thoracic region between the fifth ribs, which can continue to develop and form mammary glands, the rest of them are atrophied and disappear. If one or more of the remaining pairs of breast primordia do not disappear, an extra breast or nipple is formed, which is called a parametrium (multiple breasts or multiple nipples). Parametrial breasts can occur in both men and women, and most have only one pair, but there may be a single pair or more than one pair. They are commonly found in the armpit or forehead, forming a localized bulge like a lump, with a nipple-like protrusion in the central part, or just a halo-like pigmentation, with a soft, fat-like texture and sometimes a glandular tissue-like tenderness, which can be painful to the touch, with unclear borders. If there are nipples and glands, it is called complete parametrium; if there are only nipples and no glands, or if there are only symmetrical skin pigmentation on both sides and no nipples, it is called incomplete parametrium. The complete parametrium is commonly found in the armpit and is larger in size. Like the mammary gland, it is affected by endocrine hormones and can change periodically with menstrual flow. Incomplete parametrium can occur on the chest or other parts of the body, and is smaller in size, usually with only a secondary nipple, and is more affected by endocrine hormones. There is no need to be alarmed by the presence of parastomas, and smaller parastomas with no obvious symptoms do not need to be treated. If you have an incomplete parametrium, you will usually feel nothing and rarely experience any lesions; if you have a complete parametrium, you should be aware of the changes in the parametrium. Benign or malignant tumors can occur in the parametrium, but they are less common. If the gland gradually increases in size, is painful, or if local discomfort affects life or appearance, or if an abnormal lump is found in the parametrium and a benign or malignant tumor is suspected, you should consult a doctor and have the parametrium surgically removed if necessary.