7 Things That Might Cause Your Breasts to Get Bigger

Breast size is the result of a combination of factors. While your genes have the biggest influence, other lifestyle factors can come into play, too.

Large breasts are both a blessing and a curse. They're either regaled or minimized and hidden, depending on the culture in which you are raised. Big breasts seem voluptuous and stunning in some outfits, but they can also be a challenge when you're trying to exercise.

Read more: Can You Make Your Breasts Smaller With Exercise?

But what, exactly, determines breast size? It turns out that a variety of factors can come into play, including family history, natural estrogen levels and certain medications, including birth control.

1. Genetics

Large breasts may simply be the luck of the draw — or an unfortunate accident, depending on how you look at it — that you can chalk up mainly to genetics. Breast size is heritable, according to a June 2012 study in BMC Medical Genetics, which means your size is determined in part by the body type of not only your mother, but your father and more extensive family line as well.

A girl's breasts grow and change for several years after she hits puberty; someone who has smaller breasts at age 12, for example, may end up having large breasts by the time she is 16. You might also have larger breasts if you are overweight, with more of a fatty layer surrounding your breast tissue.

2. Hormonal Changes

Hormonal changes can cause people of both genders to develop large breasts. Females develop larger breasts during puberty, when estrogen levels rise. And of course pregnancy and lactation can also cause your breasts to become bigger due to hormonal changes that prepare your body for nourishing a baby, per the American Pregnancy Association 3.

Too much estrogen can also cause males to have large breasts, a condition called gynecomastia. Baby boys sometimes have swollen breast tissue immediately after birth due to the circulation of excess estrogen in their bodies. Pubescent and adult males who have a hormonal imbalance may also develop large, female-looking breasts, according to the National Library of Medicine 146. Treatment varies based on the underlying cause of the imbalance.

3. Certain Drugs

Drug use, in the illegal sense as well as the use of prescription medications and medical treatments, can cause large breasts in both men and women. One example is risperidone, an antipsychotic medication that carries the rare side effect of enlarged breast tissue, according to the National Library of Medicine 46.

The Mayo Clinic explains that chemotherapy, marijuana and anabolic steroids can also cause large breasts, though these more often cause male gynecomastia than breast enlargement in women 15.

Read more: Drugs That Could Cause Gynecomastia

4. Gigantomastia

This rather uncommon condition sounds like what is is: enormous breast growth that can occur during puberty, pregnancy or when taking certain drugs 3.

According to the Genetic and Rare Diseases Information Center, gigantomastia causes breast and back pain, posture issues and can lead to infection and nerve injury 10. "The more common term for this condition is breast hypertrophy or macromastia, and it refers to an excessive amount of breast tissue," explains Amy Fitzpatrick, MD, an internal medicine physician at Boston Medical Center 9.

Hormonal or genetic factors may be behind a case of gigantomastia, whose treatment usually involves breast reduction and possible mastectomy if growth recurs after the initial surgery.

5. Pregnancy and Breastfeeding

Of course your belly swells considerably as your baby-to-be grows, but during pregnancy a woman's breasts also get bigger in order to feed her newborn. In fact, breast changes and sensitivity are one of the first signs of pregnancy, according to Johns Hopkins Medicine 37. The changes that signal pregnancy may also include tenderness, a darkening of the nipple area and more pronounced veins along the sides of your breasts.

And when it's time to breastfeed, you can expect swelling, tingling and occasional engorgement or enlarged breasts due to the production of breast milk, says the American Academy of Pediatrics 8.

6. Weight Gain

Extreme weight gain, whether due to lifestyle factors or pregnancy, can show up in the fatty tissue of the breast area, notes Dr. Fitzpatrick. However, just because a woman has large breasts does not necessarily mean she is overweight.

Read more: 9 Things You DON'T Have to Do to Lose Weight

7. Birth Control

Yup, the hormones in some birth control pills can change the size of your breasts. "Exogenous hormones can contribute," confirms Dr. Fitzpatrick. However, the change is often short-lived and isn't permanent.

8. Medical Complications

There are certain physical conditions that can cause breasts to enlarge, notes Dr. Fitzpatrick. "Benign breast cysts and/or benign tumors like fibroadenoma may be large enough to affect breast size," she explains. But typically this is a localized occurrence (not the entire breast) and often unilateral—just on one side.

If you experience any unusual pain in your breasts or notice sudden swelling or enlargement, be sure to speak with your doctor.