A new report raises the possibility that the aluminium salts contained in many underarm deodorants could increase a woman's breast cancer risk.
Metals including aluminium salts and cadmium have recently been shown to exert oestrogen-like effects, while some also promote the growth of breast cancer cells in the laboratory, Dr Philippa D Darbre of the University of Reading in the UK notes in the Journal of Applied Toxicology.
Darbre's own research has shown that aluminium salts increase oestrogen-related gene expression in human breast cancer cells grown in the laboratory.
Given the wide variety of other substances that can mimic oestrogen, including certain pesticides, cosmetics and detergents, it is possible that aluminium salts and other inorganic oestrogen-related compounds called "metalloestrogens" can further disrupt normal hormonal signalling within the breast, Darbre says.
"There is no doubt that the human breast is now subject to a wide range of environmental oestrogenic assaults," 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 show that aluminium salts can penetrate human underarm skin even if it is unbroken.