The same nerve receptor that responds to the green paste on your sushi plate is activated by car exhaust, the smoke of a wildfire, tear gas and other chemical irritants. iStockphoto hide caption

itoggle caption iStockphoto

The origin of itch has confounded scientists for decades. Oktay Ortakcioglu/iStockphoto.com hide caption

itoggle caption Oktay Ortakcioglu/iStockphoto.com