In a recent double-blind study, cadets attending the U.S. Military Academy were separated into two groups that used either an antiperspirant or a placebo preparation. Each group was asked to apply the preparation for five consecutive nights before completing a 21-km hike. After the hike, only 21 percent of the cadets who reported using the preparation for at least three nights before the hike were diagnosed with foot blisters. The placebo group reported a 48 percent incidence of foot blisters. Researchers theorized that reducing sweating might reduce friction and consequently reduce blisters.