A study by Pan et al looked at the effect of parabens, which act as estrogens, on breast cancer.  They found that parabens stimulate the proliferation of breast cancer cells. Exposure to estrogens and to some xenoestrogens has been associated with cell proliferation and an increased risk of breast cancer. Despite evidence of estrogenicity, parabens are among the most widely used xenoestrogens in cosmetics and personal-care products.