The active ingredients are usually aluminum salts.
There's something that seems icky or potentially unhealthy about blocking sweat, like magic, and that might be why some people have wondered whether they could cause cancer.
But these worries are unfounded.
Researchers at the National Cancer Institute wrote that they "are not aware of any conclusive evidence linking the use of underarm antiperspirants or deodorants and the subsequent development of breast cancer."
They also said that the US Food and Drug Administration doesn't have any evidence supporting this fear, either.
Early research on aluminum exposure in rabbits found that it might be connected to Alzheimer's disease, but studies since then have not found this connection in animals or in humans.
We probably get more aluminum from food than antiperspirants, anyways.
You might worry that blocking sweat from being released could be a problem, too, since sweat can flush toxins from the body. But Dr. Hooman Khorasani from the Icahn School of Medicine at Mount Sinai told The New York Times that other sweat glands throughout the body can pick up the slack.
"There is not a significant buildup of biological waste with the use of antiperspirants," he said. You don't sweat only from your armpits, after all.
So if you want to keep your underarms dry, swipe on some antiperspirant. It shouldn't hurt.