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What causes goose bumps?

The fight-or-flight response pulls the physiological trigger. When you’re cold or you sense danger, your sympathetic nervous system floods your blood with epinephrine, a hormone that raises your body temperature and primes you for a physical fight. “The sympathetic nervous system also causes a reflex called piloerection, which makes the muscles attached to the base of each hair follicle contract and force the hair up,” says Horatio Wildman, MD, an assistant professor of dermatology at Cornell University. Goose bumps cause your hairs to stand up – just as porcupines raise their quills when threatened. When piloerection occurred in our hairy ancestors, it made them appear larger to enemies and kept them warm. Over the millennia, we lost the fur but not the reflex.