Most (not all!!) mammals have nipples as they feed their live young milk from their bodies made in mammary tissue. Marsupials and eutherian mammals typically have an even number of nipples arranged in pairs on both sides of their bodies, from as few as two to as many as 19 pairs. Some 5,600-6,000 species of mammals feed their young milk, and thus have mammary glands, but not all mammals have breasts (or nipples!!). In humans, the areola surrounds the nipple in a round shape and comes in varying sizes, on average 3 to 6 centimeters. The little bumps around the areola (called Montgomery glands) secrete an oil that smells like amniotic fluid to help baby use smell to find the nipple to latch on. In the center of the areola is the nipple, again in a wide variety of sizes shapes and lengths, and can be 10 to 27 millimeters (mm) wide by 1 to 10 mm in height. Its skin is similar to the areola, but has no oil glands. It has 4 to 20 pores where milk can come out. The skin of the nipple rests on a thin layer of smooth muscle, called areolar muscle fibers which are distributed in two directions: radial and circular. The muscle of Sappey responsible for circular fibers and the muscle of Meyerholz, formed by the radial fibers. Contraction of these muscles is responsible for the erecting of the nipples during stimulation and breastfeeding as well as the ejection of milk from the breast. How tight or loose these nipple muscles are may contribute to why some of us leak more than others and some don’t leak at all, but there is no way to exercise these nipple muscles!