What is it about eating Szechuan peppers that causes the lasting tingling or numbness in your mouth and lips after the burn has subsided? Sure, Capsaicin produces the burning sensation that delights hot sauce connoisseurs but there's another process at play when it comes to Szechuan peppers.
New research shows that a molecule in the Szechuan pepper, Hydroxy-alpha-sanshool, excites a certain type of tactile sensor in our skin in a way that feels like the sensors have been vibrated very quickly. University College London researchers explored this strange phenomena by brushing volunteers' lips with both ground Szechuan peppers and later a vibrating metal tool to match the level of numbness caused by the pepper. By identifying the frequency of the numbing sensation, the scientists determined that the high-sensitivity Meissner receptors in the skin were the ones fired up by the Szechuan peppers.
"Why Szechuan Peppers Make Your Lips Go Numb" (Smithsonian)