Large breasts are a physical characteristic that is either regaled or minimized and hidden, depending on the culture in which you are raised. Breast size does not correspond to an increase in milk production or any other type of prowess. Large breasts can be exacerbated by your family history, excess estrogen and medication use.
Large breasts may simply be the luck of the draw--or an unfortunate accident, depending on how you look at it--due to your genetics. TeenGrowth.com explains that your breast size is determined in part by the body type of not only your mother, but your father and more extensive family line as well. A girl's breasts grow and change for several years after she hits puberty; someone who has small breasts at age 12, for example, may end up having large breasts by the time she is 16. You might also have larger breasts if you are overweight, with more fatty layer surrounding your breast tissue.
Hormonal changes can cause people of both genders to have large breasts. Females develop larger breasts during puberty, when estrogen levels rise. Pregnancy and lactation can also cause your breasts to become large due to hormonal changes that prepare your body for nourishing a baby, according to the Ohio State University Medical Center. Too much estrogen can also cause males to have large breasts, a condition called gynecomastia. Baby boys sometimes have swollen breast tissue immediately after birth due to the circulation of excess estrogen in their bodies. Pubescent and adult males who have a hormonal imbalance may also develop large, female-looking breasts, according to the National Institutes of Health. Treatment varies according to the underlying cause of the imbalance.
Drug use, in the illegal sense as well as the use of prescription medications and medical treatments can cause large breasts in both men and women. Risperidone, an antipsychotic medication, carries the side effect of enlarged breast tissue, according to Drugs.com. The NIH explains that chemotherapy, marijuana and anabolic steroids can also cause large breasts, more often as a cause of male gynecomastia than breast enlargement in women.