Antiperspirants work by plugging underarm pores so that they don't release sweat (deodorants, on the other hand, merely mask the scent of scent of bacteria that feast on sweat once it's released). Most antiperspirants rely on some form of aluminum salt to do the plugging; clinical strength deodorants amp up this active ingredient. For example, both Secret and Secret Clinical Strength contain the ingredient aluminum zirconium tricholorohydrex, but Secret Clinical Strength features a concentration that is 25 percent higher [source: Newman].
With higher concentrations of the active ingredients, deodorant manufacturers claim that their products will provide 24-hour protection, as opposed to protection for just a few hours. However, to get maximum benefit, you must follow instructions carefully. Secret Clinical Strength, for example, should be applied at nighttime, before bed. That's to allow those aluminum-based plugs to develop overnight, when sweat is minimal. If the product is applied in the morning, the stress-related sweat that occurs as you try to walk pets, feed children and make it to work for your big presentation could overwhelm the main ingredients in the deodorant. Most people sweat just enough during the night to pull the active ingredient into the sweat gland and allow the long-lasting plugs to form. Even a morning shower won't wash away the plugs -- you're set for 24-hours of sweat-free activities.
A clinical strength antiperspirant may be an effective first defense for those who have hyperhidrosis, or extreme sweating. However, some doctors believe that only those with hyperhidrosis (estimated to be 2 percent of the population) should shell out the extra cash for clinical strength [source: Park]. For many people, though, even a little extra sweating is too much. When Proctor & Gamble was completing market research for Secret Clinical Strength, it found that 25 percent of women consider themselves "heavy sweaters" [source: Newman]. Whether women are overestimating their sweat production or just need extra help on stressful days, the successful sales numbers indicate that people are willing to spend more for a little extra sweat security.