Most body parts, like your arms, legs, feet, and ears, grow to a certain size and then stop. Your boobs, on the other hand, are a completely different story. Your breast size and shape can go change throughout your life.
Of course, your boobs tend to have a standard size that you consider your “normal.” And, while they may deviate here and there, you probably eventually come back to this size. While it’s easy to think that your cup size was predestined, there are actually a lot of things that affect boob size. Here are the biggest factors that influence the overall size of your breasts.
1. Your family history.
Your genes dictate your hair and skin color, how tall you are, and a bunch of other things including, yup, your breast size. But your genes are more likely to predict your breast baseline—not your actual size. “Women often are born with their breast size, but it can change in their lifetime,” Nazanin Khakpour, M.D., F.A.C.S., a surgical oncologist specializing in breast cancer at Moffitt Cancer Center, tells SELF. That doesn’t mean you’re guaranteed to be a C-cup if your mom and sister are, but it’s definitely more likely for you than someone who comes from a family with a history of A-cups.
2. Your weight.
Breasts are made up of supportive tissue, milk glands and ducts, and fat, and how much you have of each is unique to you. Some women have more supportive tissue than fat and vice-versa. If your breasts contain a decent amount of fat, you could see a difference in your boob size when you gain or lose weight, Sherry Ross, M.D., a women’s health expert at Providence Saint John’s Health Center in Santa Monica, CA and author of She-ology: The Definitive Guide to Women’s Intimate Health. Period., tells SELF. That said, you probably won’t see a huge change if you gain or lose a few pounds. “It usually has to be a significant weight gain or loss to change your breast size,” Dr. Ross says.
3. Pushups, bench presses, and other pectoral exercises.
If you started lifting recently and noticed your boobs seem a little perkier lately, that may be related. Doing pectoral exercises can strengthen your pecs, which sit behind your breast tissue, and can cause your boobs to push out a tiny bit more than usual, Albert Matheny, M.S., R.D., C.S.C.S., of SoHo Strength Lab and Promix Nutrition, tells SELF. Keep in mind that these exercises won’t actually increase your breast size—but they might grow the muscle behind the breast, which could make them appear a little bigger.
4. Your birth control.
Your birth control can do more than prevent unintended pregnancy and help regulate your period: Hormonal birth control methods like the pill, the shot, and the hormonal IUD can actually impact your breast size, women’s health expert Jennifer Wider, M.D., tells SELF. This is largely due to water retention, she says—and it’s unlikely to last. “It’s usually most noticeable when someone starts birth control,” Dr. Wider adds.
5. Pregnancy and breastfeeding.
Pregnancy boobs are legit phenomena—a woman’s breasts can grow several cup sizes during pregnancy thanks to hormonal changes like increases in progesterone, Dr. Khakpour says. Your breasts may swell up even more when you’re breastfeeding thanks to your milk coming in, but they typically go back to normal about three to six months after you stop nursing, Dr. Khakpour says.
And if you have a few kids, the effects may be more pronounced. “Some women may experience changes in breast size and shape after multiple births and breastfeeding,” Dr. Khakpour says.
6. Your age.
Your boobs probably aren’t the same now as they were when you were 15, and it’s likely they’ll look different down the road. Most women’s breasts will become less perky with time, and that’s totally normal, Dr. Ross says. “It’s largely due to a change in skin elasticity and stretched ligaments,” she says.
While it’s normal for your boobs to change, there’s often a reason behind it that you can pinpoint. But, if you find that you’re experiencing sudden breast changes and you don’t know why it’s important to talk to your doctor. While it’s likely due to something you haven’t thought of, it could be a sign of a tumor or growth in your breast. Again, don’t panic if you notice changes, but it’s best to get it checked out, just in case.