Remember the moment you came to know who Keyser Söze was? Or the splash down moment of the Apollo 13 crew? Yeah! Those Goosebumps moments! Have you ever wondered what actually makes you raise your body’s hair in such occasions?
Goosebumps are triggered when you encounter strong emotions – Especially in movies, when you watch the protagonist makes a sudden discovery or when a lively 3D dinosaur roars next to you. The body reacts to the sudden emotional changes by pumping adrenaline into your blood. This contracts your Arrector pili muscle. These muscles are attached to you hair follicles and when it contracts, it shoots your hair straight. The same thing happens when you are threatened by someone or when you feel cold. The hair stands up straight to regulate the body temperature by forming a tiny insulation layer around the body. (This is a vestigial reflex, which is retained from our ancestors.)
Every time you have an unexpected adrenaline rush, this vestigial reflex is triggered. Fight-or-flight is one such sympathetic response that produces that sudden rush of adrenaline in your body when threatened.
A cat is a good example. Threaten your neighbor’s kitty and experiment it. When threatened, the Fight-or-flight response in the cat kicks in the adrenaline to raise its hair to look menacing and little bit bigger in size. This happens in most of the mammals too.
Though they are of no use for humans now (as we are not as hairy as our ancestors are, and obviously, we have no terrifying enemies to intimidate), it’s kinda fun to experience it every time.