A recent reference in the Journal of Applied Toxicology about aluminum salts and breast cancer is worth some discusssion.
In every class we teach, the question always comes up, do deodorants cause breast cancer. This is the most recent interesting research we have found - the answer seems to be yes! Aluminum Salts have estrogen effects in the body. Most researchers agree that estrogen activity and breast cancer are related. Putting an active estrogen on your underarms could effect the breast tissue.
Here's a quote from Philippa D Darby of the University of Reading in the UK. "..it is possible that aluminum salts and other inorganic estrogen-related compounds called "metalloestrogens" can further disrupt normal hormonal signaling within the breast, Darby says. "There is no doubt that the human breast is now subject to a wide range of environmental estrogenic insults," she writes.
What is particularly concerning about aluminium, according to Darby, is the fact that it is applied to the underarm, close to the breast, and left on the skin. Deodorants also are frequently used after shaving, making it easier for aluminium salts to enter the blood stream. Studies also have demonstrated that aluminium salts can penetrate human underarm skin even if it is unbroken.
Many of us are very commited to not smelling bad, there are deodorants out there without aluminum. Make sure that what you are using does not have aluminum salts.