Here’s How Your Breasts Can Change During Your Menstrual Cycle

If your breasts came with an owner's manual, one of the first things it would say: The terms of your endowment will change. One day your boobs can be plump and perky, and the next, not so much. So why all the shape-shifting? 

Here's what you need to know about how your breasts change during your menstrual cycle, especially during and after your period.

What Happens During the Menstrual Cycle

The menstrual cycle is a sequence of events that prepare the body for pregnancy. It depends on interactions between the brain and reproductive system involving the hormones estrogen, progesterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH).

The menstrual cycle begins with menstruation, also called a period, when estrogen and progesterone levels are low. During a period, the uterus sheds its endometrial lining—the tissue that lines the inside of the uterus—through the vagina. Typically, a period lasts four to eight days and occurs every 24 to 38 days. 

Following menstruation, the ovaries produce estrogen, triggering the release of LH and subsequently leading the ovary to release an egg, also called ovulation. Estrogen and progesterone levels rise, allowing the endometrial lining to become thick. That prepares the uterus for a fertilized egg to attach itself to the tissue, beginning pregnancy. 

However, the menstrual cycle begins again if the egg is not fertilized and you do not become pregnant.

The changing hormones during the menstrual cycle cause all sorts of symptoms, including breast changes.

Hormonal Changes During Your Menstrual Cycle

The leading cause of breast changes: The ebb and flow of hormones throughout your menstrual cycle. 

"Hormones affect many aspects of our breasts—it's what inspired their development in the first place," said Rebecca Booth, MD, a board-certified OB-GYN in Louisville, Ky., and author of The Venus Week.

During your menstrual cycle, the hormones progesterone and estrogen rise and fall and may be the reason behind changes in your breasts. For example, estrogen stimulates the growth of milk ducts, while progesterone stimulates the formation of milk glands. The glands will enlarge to prepare for pregnancy, and if you don't become pregnant, they will return to their usual size.

"Most [people] will notice differences across their monthly cycle, and it's completely normal," added Dr. Booth.

Although, keep in mind: If your breasts are a borderline size B, you're not suddenly going to wake up with a pair of DDs.

How Your Breasts Change During Your Period

At the beginning of your period, estrogen and progesterone levels are low. Estrogen begins to rise, peaking just before mid-cycle. And if your menstrual cycle lasts 28 days, progesterone level will typically peak around the 21st day. That rise in hormones causes the growth of the breast lobules, also known as milk glands.

During the first few days of your cycle (when your period starts), the texture of your boobs may suddenly feel uneven and nodular. Why the sudden rough patch? 

"During menstruation, breasts may feel lumpier as milk glands enlarge in preparation for a possible pregnancy," explained Sara Gottfried, MD, a board-certified OB-GYN in Berkeley, Calif., and author of The Hormone Cure.

In addition to feeling lumpy, your breasts may feel swollen, painful, or tender. However, those feelings aren't permanent. As soon as your body realizes you're not pregnant, your breasts will smooth out, and those symptoms will subside, added Dr. Gottfried.  

Toward the end of your period, your boobs may suddenly pull a disappearing act.  

"Breasts are at their lowest volume at this time because estrogen and progesterone are at their lowest," explained Dr. Gottfried. "They also tend to soften up towards the end of bleeding." 

Breasts Changes After Your Period

In the luteal phase—which occurs after ovulation—generally around day 15 and up through the end of your cycle, expect to be at your largest cup size. 

"Progesterone is really peaking, so this is a time associated with the largest breast size and density," said Dr. Booth.

Other Causes for Breast Changes

Aside from the monthly rhythm of your menstrual cycle, there are other times when your hormones fluctuate, which can cause changes to your chest.

Pregnancy

When you're pregnant, the glands in your breasts that produce milk will swell, enlarging your breasts and making them feel lumpy.

You may have developed mastitis if you are breastfeeding and notice other changes in your breasts, like redness or tenderness. Mastitis is an infection that healthcare providers often treat with antibiotics.

Approaching Menopause

As you approach menopause, your hormones will fluctuate. Even though you no longer have a menstrual cycle, your breasts can still be tender and lumpy from the fluctuation of hormones. You may notice these issues will resolve after menopause.

Cancer

Not all breast changes are causes for concern, but you may want to see a healthcare professional if you are experiencing any of the following symptoms:

• Lump in your breast/under your arm
• Nipple changes or discharge
• Itchy, red, dimpled, or puckered skin

If you notice these changes, a healthcare provider will examine the breast and take imaging such as a mammogram, ultrasound or sometimes an MRI to determine if you are at risk for breast cancer.

A Quick Review

Your breasts go through a series of changes throughout your life. The hormonal changes your body experiences can cause your breasts to feel lumpy, small, or swollen, depending on where you are in your menstrual cycle.

Besides the menstrual cycle, your breasts may experience changes during pregnancy or menopause. However, if you feel any abnormal lumps or other signs of breast cancer, you should consult your healthcare provider.