At issue is a substance called parabens, widely used as a germ-fighting preservative in cosmetics such as deodorants and antiperspirants.
British researchers examined breast tissue samples from 40 women who had mastectomies and found traces of parabens are widespread in tissues, even in women who said they had never used underarm products.
They say the implications in nonusers is that parabens must have come from another product or products.
Parabens can also be found in lotions, makeup and sunscreen.
Scientists in the Journal of Applied Toxicology say their study does not show direct cause and effect, but they suggest women should cut down or cut out the use of cosmetic products as much as possible.
The American Cancer Society says more research is needed.
