Like many spice junkies, Marco Tizzano, an investigator at the Monell Chemical Senses center, once believed he could develop a tolerance to the burning, painful sensations generated by eating chilis. But as a chef and researcher in chemosensory sensations, he now knows better. Tizzano explains how capsaicin creates a chemical cascade inside your body and why emotions might make chili lovers think they can handle the heat.