|Medical anthropologists Sydney Singer and Soma Grismaijer -- authors of Dressed to Kill: The Link Between Breast Cancer and Bras -- conducted a study of over 4,000 women, and found that women who do not wear bras have a much lower risk of breast cancer.
Their findings included:
Women who wore their bras 24 hours per day had a 3 out of 4 chance of developing breast cancer
Women who wore bras more than 12 hour per day, but not to bed, had a 1 out of 7 risk
Women who wore their bras less than 12 hours per day had a 1 out of 52 risk
Women who wore bras rarely or never had a 1 out of 168 chance of getting breast cancer
The overall difference between women who wore their bras 24-hours a day and those who did not wear bras at all was a 125-fold difference. Based on the results of this study, the link between bras and breast cancer is about three times greater than the link between cigarette smoking and cancer.