Parabens
Parabens in their many forms (methylparaben, propylparaben, ethylparaben, or butylparaben) are a class of artificial preservatives widely used in cosmetics and personal care products that are being investigated for their possible role in breast cancer. Parabens mimic the activity of estrogen in the body. Since estrogen promotes the growth of breast cancer cells and a woman is eight times more likely to develop breast cancer in the part of the breast closest to the underarm, scientists are studying the connection.
Although parabens have estrogen-like properties, the estrogens that are made in the body are hundreds of times stronger. So, natural estrogens (or those taken as hormone replacement) are much more likely to play a role in breast cancer development.