Studies have shown that restroom automatic dryers inhibit the growth of bacteria on the skin by drying the skin more effectively than paper towels. Rub your hands with paper towels and you are probably missing some nooks and crannies that warm air from restroom hand dryers can reach. Even though you may think your skin looks dry and feels dry after using a paper towel, there are probably some moist places where bacteria could thrive.
Warm air hand dryers are more likely to get the hands thoroughly dry, as long as you give them enough time. The average model hand dryer takes about 30 seconds to dry hands--count to 30 when using an air dryer to make sure you get dry enough to keep the bacteria in check.