Most deodorants contain Aluminium and one can tell this by reading what active ingredients are listed at the back of the cover. The aluminium component is thought to get easily absorbed by the skin and then cause oestrogen-like (hormonal) effects which lead to breast cancer.
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Because of the concern for aluminum there are a lot more brands coming out without it. The only way to know for sure if it is in the brand or not is to read the package. I know that Burt's Bee has some and so does some others.
A deodorant is a substance applied to the body to prevent body odor caused by the bacterial breakdown of perspiration in armpits, feet, and other areas of the body. A subgroup of deodorants, antiperspirants,...