Well, not all stress makes us sick. Stress can motivate and energize us—it helps us perform better in front of an audience or get psyched for an adventure, like white-water rafting on the Colorado River in chilly November (shout-out to Mike, Eric, and Frederique!) or skydiving from 13,000 feet (“terrifying” and “freeing” says my brave niece, Laura, pictured). Not surprisingly, skydiving triggers a “fight-or-flight” (literally!) stress hormone response. In one study, 39 men and women who tandem jumped for the first time had increases in cortisol, stress catecholamines, inflammatory cytokines (IL-12 and interferon-gamma), and natural killer cell numbers and gene expression. Manfred Schedlowski, a German researcher I heard at a conference way back in 1993, [...]