Goosebumps may also spread across the skin in "hair-raising" moments of high emotion, a tingly wave you feel thanks to the pilomotor reflex. Back in the day, humans faced many predators. When threatened, the pilomotor reflex would kick in and puff out the body hair, making a person appear larger and more imposing. The raised hair also trapped an extra layer of air near the body to retain warmth. We modern humans have retained this porcupine-like reflex. It no longer provides much help during cold snaps, since we don't have as much body hair as our ancient ancestors. So what good does it do us in a stressful moment? Like blushing, you could consider goosebumps another way your body clues you in to stresses or dangers.
