Foam soaps may be a bit more fun to dispense than liquids, but that doesn't mean they kill germs better. In fact, despite their increased usage in hospitals, schools, and other public buildings, they may actually be inferior to the old liquid standby, according to a study in the American Journal of Infection Control.
For the experiment, five people washed their hands for six seconds using one pump of liquid detergent-based soap before drying them on paper towels for four seconds, and another five used foam soap. The concentration of germs on the hands afterward were quantified on a 1-4 scale.
After using foam soap, the amount of bacteria went from a 3.6 to a 2.6 on average, which wasn't statistically significant. The liquid soap, on the other hand, led to a dramatic decline of 3.8 to 1.2. Two follow-up studies produced the same findings.
It's possible that foam soap is less effective simply because with all those bubbles, there's just less soap in each dollop of the product. "Our data suggest that the use of foam soaps for handwashing may give a false sense of hand decontamination and potentially lead to the spread of resistant bacteria," the authors conclude.
But since the study only involved five people, it's hard to draw conclusions, hand hygiene expert Dr. Guenter Kampf told Reuters. If you want to get your hands as germ-free as possible, though, he said the best kinds of soaps are probably "alcohol-based hand rubs or gels," followed by antimicrobial soaps and then plain soaps. The FDA, however, has reported that a lot of antimicrobial soaps may not actually be any better than regular ones.
Don't overanalyze this, though: Soap choice may matter more to places like hospitals that have to keep germs from spreading than in your home, Kampf said. "For domestic use it may not make a difference whether a foam or liquid soap is used because cleaning of the hands is the main purpose of washing them."