Hayes says the heat threshold for mammals is 42 degrees Celsius (about 108 degrees Fahrenheit). Chile plants figured out a way to fool the body's temperature sensors via the chemical capsaicin, which works on the receptor TRPV1 (Hayes calls it a "molecular thermometer"). Basically, the chemical punks the body into thinking it's burning tissue. In fact, the reaction with capsaicin is an inflammatory response, more like an allergy.
So how do restaurant workers, who have to cut hot peppers every day, deal with the faux burn? "You just wash with soap and hot water," says Alex Bhowjani, supervisor at Bun Mee, a Vietnamese sandwich joint in San Francisco that serves up to 600 jalapeño-packed banh mi per day. Restaurant cooks don't have time to bother with the fancy solutions floating around the Internet, ranging from applying vegetable oil to soaking in whole milk. Bhowjani says you stop noticing after a while. "You just get used to it." There is evidence this is true.
For home cooks, Hayes happens to agree with Bhowjani: The best remedy is actually washing with soap and water, although Hayes insists on cold water, not hot. The soap binds with the capsaicin to wash it away, and the cold water lowers the temperature of your hands so that TRPV1 isn't activated.
As for all the folk remedies out there, Hayes says they're a mixed bag. Milk and other dairy products? Fine, but probably mostly effective because they're cold. Tomatoes, vinegar, lemon, or lime? "It turns out the molecular thermometer works by sensing hydrogen atoms, so acids are the worst thing you can use." [Ed. note: Acids usually "donate" hydrogen ions to solutions.] Vegetable oil? It'll take the capsaicin off your hands but won't reduce the temperature unless it's cold. Rubbing alcohol? "That's an irritant in and of itself. Don't add an irritant to an irritated place!" Gasoline? "I guess it would work, but it's not very safe. You gonna put it in your sink?"
Topical skin-numbing creams containing benzocaine or tetracaine are, in fact, effective. Hayes says they work by temporarily shutting down the nerves that register pain.