Horripilation, the pilomotor reflex better known as goosebumps, begins when the sympathetic nervous system releases norepinephrine onto tiny erector pili muscles that anchor the skin’s basement membrane to hair follicles. Recent anatomy shows one muscle often controls a cluster of follicles, and its contraction squeezes sebaceous glands to push oil to the surface. The follicle’s deep bulb gives the muscle a firm anchor to pull against. In furred mammals the reflex traps insulating air and makes animals look bigger, from porcupines and cats to sea otters facing sharks. In nearly hairless humans it is a vestigial reflex.

A bug on the arm triggers local goosebumps, while cold or strong emotion sets off a whole body response, though sensor studies found reported music chills rarely involve actual muscle contraction. Goosebumps can signal temporal lobe epilepsy or autonomic hyperreflexia, and opiate withdrawal produces so much piloerection that skin resembles a plucked turkey, the origin of going cold turkey. In 1500s London, Winchester geese meant sex workers in Southwark licensed by the Bishop of Winchester, and goose bumps took on a whispered link to syphilis.

• The hair follicle has four parts: bulb, suprabulbar area, isthmus, and infundibulum
• Yohimbine, a tree bark alkaloid, triggers goosebumps by releasing norepinephrine
• Several languages name the reflex after chickens or hens, Hebrew after a duck, and Russian and Ukrainian after crawling ants
• Voluntarily generated piloerection is an innate ability, usually discovered by accident
• People who can raise goosebumps at will tend to score high in openness to experience