Is Breast Size Hereditary?


Ever wonder what determines your boob size and shape? Did you get them from your Mom? Are they the result of environment, diet, even activity level?

Well, like most body parts, the size and shape of our breasts is largely genetic.

But that doesn’t mean that:

  1. They can’t change (in fact they do, quite often)
  2. There are no other factors that influence their size.

Yes, Breasts Are Largely Influenced by Genetic Factors

So why is one woman a 30B and another woman a 36E? Does it signify anything?

You can mostly blame (or thank) your genes for both the size and shape of your breasts, and even the composition of your breast tissue. 

According to Nature, “Breast size is a highly heritable trait. A twin study previously estimated the heritability of bra cup size to be 56%. Several genome-wide association studies have also identified common genetic variants associated with breast size.”

In 2012, in the journal BMC Medical Genetics, researchers identified seven genetic markers linked with a woman's breast size. While it was known already that breast size is in part heritable, the study was the first to find specific genetic factors that are associated with differences in breast size, the researchers said.

What Other Factors Influence Breast Size?

So we know genes play a big role, but what other factors are important?

Body weight is a big one. To understand why, it helps to learn what breasts are made of. Your breasts contain fatty tissue (also known as adipose tissue). Adipose tissue extends from the collarbone down to the underarm and across the middle of the ribcage.

The presence of fat tissue in the breasts means your breast size can fluctuate with weight gain or loss. It can also mean that individuals with higher body fat will often have larger breasts.

What Else Causes Breast Size to Change?

While breast size is mostly determined by your genes, that doesn’t mean it stays the same throughout your life. Indeed, most women experience many changes. Here are some of the key causes of changes to your breast size (and shape).

Age: Puberty to Menopause

From puberty through maturity and into menopause, our bodies go through many changes. These developmental stages are often ushered in by hormonal changes, which can definitely affect your boobs. 

Menstrual Cycle

Hormones also play a major role in your menstrual cycle and these can cause monthly changes to your breast size. Many women especially notice breast swelling and tenderness just before their period as part of their premenstrual symptoms (PMS) and/or during ovulation, around the middle of their cycle.

Hormonal Birth Control

Hormonal birth control is used to prevent unwanted pregnancy but the hormones in play can also cause fluid retention and breast swelling in some women. These effects are often stronger in the first few months of taking a new birth control pill.


During pregnancy, your breasts may double or triple in size. According to the Mayo Clinic,

“One of the first signs of pregnancy is an increase in breast size. As early as two weeks after conception, your breasts start to grow and change in preparation for producing milk. Stimulated by the hormones estrogen and progesterone, the milk-producing glands inside your breasts get bigger and fatty tissue increases slightly.

By the end of your first trimester, your breasts and nipples will be noticeably larger, and they may keep growing throughout your pregnancy. Breast enlargement accounts for at least a pound of the weight you gain while pregnant.”

Your breasts may remain enlarged for a while after birth.

What You Can Do to Change Breast Size

So is there anything you can do to change your breast size?

Quit Smoking

Among the many health risks associated with smoking is a loss in skin elasticity, which can affect the delicate skin and breast tissue. This can cause breasts to sag. Some women perceive this as a change in size, though it’s really more related to shape unless accompanied by other changes.

Consider the Pros & Cons of Breast Augmentation

One of the more obvious ways to alter your breast size is to go under the surgical knife. Whether it’s a breast augmentation or a desire to reduce breast size, this will cause a more extreme and often permanent change to your breast size.

Some women with larger breasts experience back and neck pain as a result of their breasts. So, while the reasons for breast augmentations can go beyond the cosmetic, we generally advocate discussing all the pros and cons with your healthcare provider. 

Try Different Bra Styles

Different styles of bras promise to increase your cleavage, while others claim to minimize your breast size. It’s definitely worth trying different styles of bra to see what makes you feel most comfortable with your silhouette, and in your skin.

We strongly recommend getting properly fitted— an ill-fitting bra can make you feel really out of sorts. The wrong size or fit of bra will ruin your day but it can also make you feel unhappy with the size and shape of your bust. The right bra can be a game-changer.