One time only
On May of 2015, A certain hypnotist by the name of Chris Jones came on and Howie was the volunteer for the hypnotist act. Chris hypnotize Howie into thinking he had gloves on his hands. Chris then ask Howie to shake his hands while Howie being in the influence of "wearing gloves", after that Howie began shaking each of the 3 judges' hands that surprised them as this is the first and only time that Howie Mandel shook with his bare hands (without using hand sanitizer).
The act itself
Chris Jones: Howie Mandel Gets Hypnotized to Shake Hands - America's Got Talent 2015