Aluminum
Aluminum-based compounds are the active ingredients in antiperspirants. They block the sweat glands to keep sweat from getting to the skin’s surface. Some research has suggested that these aluminum compounds may be absorbed by the skin and cause changes in estrogen receptors of breast cells. Because estrogen can promote the growth of both cancer and non-cancer breast cells, some scientists have suggested that using the aluminum-based compounds in antiperspirants may be a risk factor for the development of breast cancer.
Studies have looked at aluminum content of breast tissue, and aluminum absorption through the skin, but no clear link to breast cancer has been made. Researchers continue to look at this possible breast cancer risk factor and more studies are needed. (American Cancer Society)