The Science Behind Breast Pain During Your Cycle

Breast pain got you down? If you’re like many women, your breasts and nipples can change drastically over the course of your menstrual cycle. Some days, it feels like you could put a clothespin over your nipple and you’d barely notice it. Other days, the fabric of your t-shirt barely grazing your nipples can feel like a razor blade.

The hormones progesterone and estrogen are responsible for cyclical changes in the way your breasts and nipples feel throughout the month. To understand why, let’s start by reviewing the way these hormones change during the menstrual cycle.

Hormonal changes throughout the cycle

The cycle is divided into two phases: the follicular phase, which begins on the first day of your period and ends at ovulation, and the luteal phase, which begins after ovulation and lasts until your next period. During the follicular phase of the cycle, estrogen rises and peaks, falls just before ovulation, and increases slightly in the luteal phase. Progesterone begins rising just before ovulation, and peaks midway in the luteal phase. If pregnancy doesn’t occur, progesterone plummets which prompts your next period to begin.

Your breasts go through a cycle, too

Your breasts go through a cycle of their own. To understand how your cycle impacts the way your breasts feel, let’s review what the breast really is. Its primary function is to provide milk to babies, and the physiology of the breast can be understood according to this function. The internal breast structure is kind of like a drainage system: milk is produced in sacs of mammary cells, called alveioli. These alveoli are connected to a series of ducts, which drain towards the nipple. This drainage system is surrounded by connective tissue and fat, which provude strucutural support and assist in mammary cell function.

At the beginning of the follicular phase, your progesterone levels are low. For most women, this means that there isn’t much going on in their breasts or nipples. But estrogen rises as you approach ovulation. One of the impacts of estrogens is an increase in the number of progesterone receptors in the breasts, setting the stage for progesterone to do its job during the luteal phase of the cycle. As progesterone levels rise, it drives mammary cells and alveoli to multiply in preparation for a possible pregnancy.

If you become pregnant, your progesterone levels continue to rise, which drives continued—and quite visible!—growth of your mammary cells during pregnancy. If no pregnancy occurs, progesterone levels fall, and the newly created cells start dying. As the mammary cells die, they cannot be shed and discarded in the same way that the uterine lining is during your period. Instead, the dying mammary cells are broken down and eliminated by scavender cells and surrounding tissue. As the cells die, the breast structure returns to its earlier architecture, and a new cycle starts again.

PMS or Pregnancy?

It’s common to feel some breast pain right around the time that progesterone peaks, or about a week before your period is due. If you have a 28 day cycle, you might experience breast or nipple tenderness around day 21. It should subside as hormone levels plummet, just before or during your period.

Breast pain can also be an early pregnancy sign. Is there a way to tell the difference between normal premenstrual breast soreness and soreness that indicates pregnancy? While there’s no conclusive test, there are a few possible clues. During early pregnancy, soreness often extends to the whole breast, rather than the nipple only. And it tends to last for an extended period of time—often throughout the entire first trimester—whereas premenstrual breast soreness usually lasts for only a few days.




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