Nipple and areola

The nipple does not have a single hole: it looks more like the face of a showerhead. Each lactiferous duct, one of the tubes that carry milk, opens through its own pore, barely half a millimeter across, and each pore has a tiny sphincter, that is, a ring of muscle that closes off the passage and keeps milk from dripping out during breastfeeding.

Around the nipple is the areola, the circular, more pigmented area. On the outside it is covered by stratified squamous epithelium, the same kind of layered skin found on the rest of the body. Its color varies enormously from one person to another, from pink to nearly black, and it darkens at puberty and during pregnancy.

The little bumps you can see along the rim of the areola have a name: they are the tubercles of Morgagni, the openings of the Montgomery glands, which release a substance that lubricates the area during breastfeeding. And underneath the nipple and the areola there are bundles of smooth muscle, the kind of muscle you cannot control at will: they are what make the nipple erect.