In the late 1880s, various chemists got the idea of using aluminum salts in an effort to stop the flow of sweat from our armpits. How this actually works is kind of ingenious. Sweat, as it turns out, is pushed out of our pores by pressure created by charged particles, called ions, which want to move and join with particles of the opposite charge. But if you apply aluminum salts to the armpits, the opposite occurs, and your body draws ions from the antiperspirant into the pores, where they form plugs, which block the flow of water to the skin [sources: Williams and Schmitt, Newman].
The first trademarked product to exploit this phenomenon was a liquid called Everdry, which appeared on the market in 1903. Users applied it with a cotton ball, which was a bit messy. Another breakthrough antiperspirant was Odorono, a liquid preparation, which contained aluminum chloride. It was so effective that it actually reduced perspiration by about 60 to 70 percent, and lasted for up to three days [sources: Laden; Everts]. But it had a few downsides, too. It contained an acid that irritated the skin inside users' armpits, and sometimes even ate through their clothing [source: Everts].
Fortunately, antiperspirant makers have refined their formulas considerably since then, so they're less harsh. The trade-off is that the modern antiperspirants are actually slightly less effective — generally decreasing perspiration between 30 and 50 percent in the course of a day. While that may not seem so great, it's enough to prevent sweat from seeping into a person's clothing and creating conspicuous stains [source: Laden].
Cameron Diaz isn't the only person who worries that antiperspirants are somehow bad for your health. The Internet has been rife with rumors that the aluminum in antiperspirants can increase the risk of breast cancer and Alzheimer's disease, if it is absorbed by the body through a cut in the skin [sources: Grossman, Moninger].
But the National Cancer Institute says it is aware of no studies that conclusively link aluminum in antiperspirants to breast cancer, and the Alzheimer's Association says that studies have failed to confirm a link between the disease and everyday exposure to aluminum. Similarly, the rumor that chemicals called parabens, which have been found in breast tumors, are linked to antiperspirant use turns out to be shaky, since most major brands are paraben-free [source: Moninger].