While it’s easy to think that your cup size was predestined, there are actually a lot of things that affect it. Here are the biggest factors that determine the overall size of your breasts.
Most body parts grow to a certain size and then stop. Your breast size, on the other hand, is a completely different story. Your boobs can actually change size and shape throughout your life. So what determines breast size, anyway?
1. Your family history
Just as your genes help dictate your hair and skin color, how tall you are, and a bunch of other characteristics, they also have some impact on your breast size. That doesn’t mean you’re guaranteed to be a C-cup if other people in your immediate family are, but it’s definitely more likely for you than someone who comes from a family with a history of A-cups.
“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. In short, family history is one indicator of many, and there are other factors that contribute to the fluctuations that can happen over time.
2. Your weight
Your breasts are a complex part of your anatomy, made up of supportive or connective tissue, milk glands and ducts, and fatty tissue. How much of each tissue type you have is unique to you. Some people have more supportive tissue than fat and vice-versa. If your breasts contain a higher concentration of fatty tissue, 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, California, and author of She-ology: The Definitive Guide to Women’s Intimate Health. Period., tells SELF. That said, you probably won’t see a drastic 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. Your workout routine
If you started lifting recently and noticed your boobs seem a little perkier, that may be related. Doing pectoral exercises can strengthen your pecs, which are four major muscles that sit behind your breast tissue and facilitate deep breathing and arm movement. If your pecs bulk up a little, this 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 period
Your menstrual cycle can bring pretty distinct changes to your breast size, texture, and shape. During the first half of your cycle, your body produces estrogen, a hormone that brings about ovulation and stimulates the milk ducts in the breasts, Hopkins Medicine explains. But in the second half of the cycle (as you get closer to your period), progesterone stimulates the formation of milk glands, which is said to cause swelling (and even a little soreness), according to Hopkins Medicine. This might prompt you to wonder why your boobs have suddenly gotten bigger. While you’re on your period, your breasts might also feel a bit lumpier than usual, but this isn’t a cause for concern – your glands are simply enlarging to prepare for a possible pregnancy, according to Hopkins Medicine. Ultimately, your breasts will return to their normal size and texture.