Breasts are secondary sex characteristics, which are features that distinguish the sexes but are not directly related to reproduction.
Most women think of them as a key component of their sexual selves, and self-image is often affected by reactions to their size and shape. Society’s fixation on sexualizing breasts makes it difficult to think about them as a functioning body part, especially in a culture that heavily markets breast enlargement/augmentation.
Like fingerprints, no two breasts are alike, and there is no “perfect” pair. Breasts come in all sizes and shapes: large, small, firm, lumpy. You can see that your breasts may be slightly different from each other in size or shape, which is totally normal. You may notice areas of hardness or softness, different textures, and varying areas of sensitivity. Nipples may lie flat, stick out, or retract (be inverted).
The areola (area surrounding the nipple) may be large or small, darker or lighter, and it usually has little bumps just under the skin. These bumps are the sebaceous glands, which secrete a lubricant that protects the nipple during breastfeeding. Sometimes there are hairs near the edge of the areola.
Breast size is not related to the sexual responsiveness of the breast or to the amount of milk produced after giving birth; small-breasted women are able to breastfeed just fine.
During pregnancy and breastfeeding, breasts often enlarge considerably. They may also swell during sexual arousal. Weight gain and loss also affect breast size.
Breasts usually become droopier over the years as skin becomes less elastic and milk (mammary) glands get smaller. This happens even faster after childbirth (when breastfeeding is completed) and again after menopause, when the milk glands are no longer stimulated to grow.
Because breasts react to sex hormones produced by the ovaries, you may notice pronounced changes during the menstrual cycle, such as your breasts becoming bigger or fuller right before you menstruate. This fullness sometimes produces tenderness that can be felt up into the armpit, in the part of the breast called the tail.
Around the time the ovaries begin producing estrogen (a year or two before menstrual periods start), the breasts respond by growing. At first, a firm mass develops directly behind the nipple. This is called the bud. As puberty progresses, the ductal tissue in the bud grows out into the fatty tissue, forming branches and lobules to make up the glandular portion of the breast.
The fatty and fibrous tissues that support it (stroma) also increase during puberty. Most of this growth happens early, but slower growth continues during the teen years. One breast may develop more quickly than the other.
With the great increase of sex hormones during adolescence, the milk-producing glands in each breast start to develop and increase in size. During the reproductive years, breast tissue consists of the glandular breast lobules, which are supported by connective tissue ligaments that anchor breast tissue to the skin and to the connective tissue covering the underlying muscles. Variable amounts of fat fill the spaces between the breast lobules and the supporting ligaments.
After menopause, the glandular breast tissue is gradually replaced by fat. The amount of fat in the breast is determined partly by heredity and causes breast size to vary.