Nipple

The nipple is a central projection on the breast through which milk ducts open. In humans, nipples occur on individuals of most sexes; they form in the embryo before sex differentiation. The area around the nipple is the areola, which is typically darker and may contain small glands that lubricate the area.

Anatomy: The nipple contains the openings of lactiferous ducts from underlying mammary glands. The tissue beneath includes smooth muscle fibers (myoepithelial cells) that can contract, causing the nipple to become erect in response to cold, touch, or sexual arousal. The areola contains sebaceous glands, known as Montgomery glands, that secrete lubricating fluids during lactation. Nerve supply is rich, contributing to sensation.

Development and variation: Nipples are present in both sexes and vary in size, projection, and pigmentation. Some nipples are inverted or flatter than others. Hormonal changes during puberty, pregnancy, and lactation can alter appearance and function, including nipple size, color, and milk production readiness.

Function and clinical notes: The primary role is to deliver milk produced in the mammary glands to a nursing infant via lactation. Stimulation of the nipple can trigger the release of oxytocin, promoting milk ejection. Non-lactating nipples may experience irritation, dermatitis, or benign changes; persistent nipple discharge, a lump, or sudden changes should be evaluated by a healthcare professional.