Reader's Question

Dear Doc,
I have been wondering this for a while, but am too embarrassed to ask my mom--why do some women have small breasts while their mothers have larger breasts than they do? Does breast size increase with age, or what is it? I'm just curious; not shunning small breasted women in the search for my mate.

Doc's Answer

Breast growth in girls begins about two years prior to menarche (the start of menstrual periods) and may continue up to four more years, which is to say women’s breast generally grow for about six years. A 2010 Australian twin study found that bra size was fifty-six percent a matter of heredity (genetic). However, not everything in life is genetic, and genes are about predisposition and not destiny. So, a woman’s mother’s breast size says something about her own, but not everything.

Other things during her life may change a woman’s breast size. Since adipose (fat) makes up a good part of the breasts, significant weight loss or gain will also affect breast size in the same direction. Pregnancy, for obvious reasons related to hormonal changes and milk production, will usually enlarge a woman’s breasts. About twenty percent of women will have breast growth after menopause, and the main reason for this is weight gain.

Genes, weight, age, pregnancies, menopause and other factors all play roles in breast size. So the answer to your question about why some women have smaller breasts than their mothers is that they are not their mothers.