Most people put on either deodorant or antiperspirant before leaving the house. There are some products that perform both functions. These products are used to control sweat and odor in our underarms. There are two types of glands in our underarms, apocrine and eccrine. The eccrine glands are by far the most numerous sweat glands and are responsible for producing most of the sweat in our underarms, as well as in our entire body.

Some people wear deodorants to cover up underarm smells, but if you sweat a lot, you probably need an antiperspirant to slow down the production of underarm sweat. Our bodies are constantly producing sweat, but there are certain times when they produce a lot more. Additional sweat is produced to cool down our bodies when we are exposed to heat, physical exertion, stress or nervousness. When the sweat gland is stimulated, the cells secrete a fluid that travels from the coiled portion of the gland up through the straight duct and out onto the surface of our skin.

Solid antiperspirants are made with several ingredients, including wax, a liquid emollient and an active-ingredient compound. It's the active ingredient that gives antiperspirants their sweat-blocking power. All antiperspirants have an aluminum-based compound as their main ingredient. If you look at the back of an antiperspirant container, the aluminum-based compound is always the first ingredient listed. Here are a few of the common active ingredients:

  • Aluminum chloride
  • Aluminum zirconium tricholorohydrex glycine
  • Aluminum chlorohydrate
  • Aluminum hydroxybromide

The aluminum ions are taken into the cells that line the eccrine-gland ducts at the opening of the epidermis, the top layer of the skin, says dermatologist Dr. Eric Hanson of the University of North Carolina's Department of Dermatology. When the aluminum ions are drawn into the cells, water passes in with them. As more water flows in, the cells begin to swell, squeezing the ducts closed so that sweat can't get out.

Each cell can only draw in a certain amount of water, so eventually, the concentrations of water -- outside and inside the cells -- reach equilibrium. When this happens, the water inside the cell begins to pass back out of the cell through osmosis, and the cell's swelling goes down. This is why people have to re-apply antiperspirant. For those who suffer from excessive sweating, hyperhydrosis, aluminum chloride in high concentrations can prolong the swelling and may ultimately shrink the sweat gland, decreasing the amount of sweat it can produce.

An average over-the-counter antiperspirant might have an active-ingredient concentration of anywhere from 10 to 25 percent. The FDA requires that over-the-counter antiperspirants contain no more than 15 to 25 percent of the active ingredient, depending on what it is. The FDA also requires that all antiperspirants must decrease the average person's sweat by at least 20 percent. For those who have excessive underarm sweating, there are prescription products that contain concentrations higher than those of over-the-counter antiperspirants.

For more antiperspirant information and articles on related topics, check out the links on the next page.