Public restrooms can be a disgusting place filled with unflushed
  toilets and other repulsive smells. The rise of hand-dryers is
  only contributing to this problem, posing a more serious risk to
  public health than most people think.
  In 2018, researchers from the University of Connecticut suspected
  that hand dryers in public bathrooms may be sucking up bacteria
  from the surrounding air, and blowing it onto the freshly washed
  hands of unaware guests. To prove this hypothesis, scientists
  placed petri dishes in different locations around a bathroom, and
  then recorded any mycobacterial growth. With the hand dryers off,
  petri dishes exposed to the air in the bathroom grew one or zero
  colonies of bacteria within a span of two minutes. However, petri
  dishes exposed to the hot-air hand dryers for thirty seconds grew
  anywhere from 18 to 254 colonies.