There is a multitude of factors influencing a woman’s breast size, including genetic predispositions, changes in body weight, the natural ageing process, hormonal fluctuations, pregnancy and breastfeeding, and lifestyle factors like smoking.
Here is a closer look at each factor:
Genetics: Genetics passed down from female relatives is one of the strongest factors influencing the size of women’s breasts. You may find that people whose close relatives have large breasts are likely to inherit that trait.
Body weight: A woman’s BMI can also strongly influence the size of her breasts. The breast contains fatty tissue, so weight gain and loss impact size. Women with higher BMI tend to have larger breasts.
Age: Breasts change over a woman's lifetime. The breasts start to grow during puberty, and many women’s breasts may shrink after menopause.
Hormones: A woman’s estrogen levels can also influence the size of her breasts. Estrogen stimulates breast tissue growth, so having low estrogen or high testosterone can cause small or underdeveloped breasts.
Pregnancy and breastfeeding: A woman’s breasts may become significantly bigger during pregnancy. Pregnancy causes mammary glands to swell in preparation for lactation. Once the baby is born and breastfeeding begins, the breasts can slightly deflate or return to their original size.
Lifestyle factors: Lifestyle choices like diet, exercise, smoking, and medications can also influence breast size to some degree. Smoking, for instance, has proven to decrease estrogen levels, and this can cause a reduction in breast size.