It is quite common to talk about hair raising personal experiences when watching an eerie movie or exposed to very cold climate conditions. This hair rising phenomenon is due to innate reflex or a psychological reaction commonly known as goose bumps. Goose bumps are messages from the brain to the skin to react to the animal oriented phenomena of fight or flight. Porcupine raising its quills on seeing a threat is a good example to understand goose bump and its nature.
Since human body cannot differentiate between real and imaginary conditions, goose bumps can be a reflex to a physical condition or a reaction to a psychological condition. Goosebumps are directly related to the adrenaline rush that flows through the body. Adrenaline rush can be triggered by fear or emotional reactions. Emotional reactions can be positive or negative, powered by intense ‘stress’ to induce the emotional welling up to trigger goose bumps.
Skin of a goose or chicken has a bump at the place where feather is attached to the skin. In the event of a hair rising phenomenon, each spot on the human skin has a bump similar to the goose bump, and this connection must have given this phenomenon its name as goose bumps.
Animals are warm-blooded and maintain stable body temperature. Animals do not display variance in temperature in excess of 2 deg even during hectic working conditions. Normal muscle and blood activities help the animals to maintain the stable temperature under different climate conditions. During extreme cold conditions, hair is used as a mechanism for heat retention. Air acts as an excellent insulator. Tiny muscles, called arrector pili muscles, exist under the skin that pulls the hair base on exposure to cold or scary conditions. Pulling of the hair base fluffs the hair or fur trapping the extra air between the skin and the environment. Air thus trapped acts as an insulator to protect the animal from cold conditions. Fluffy hair contributes to the size of the animal making it seem bigger to the threatening enemy. Due to skimpy fur, human do not exhibit a change except the hair rising phenomenon.
Scientifically, Goose bumps are called Piloerections. Piloerections are emotion based autonomic reflex reactions routed through the limbic system. Piloerections are similar to blushing or feeling butterflies in the stomach. Limbic system controls primitive drives of hunger, sex, fear, anger and aggression. Limbic system anatomically has thalamus, a major structure in control of the sensory inputs. Medial forebrain bundle and the hypothalamus play a major role in the invocation and mediation of the autonomic reflexes.
Goose bumps have been observed on head or scalp on scary occasions but goose bumps on a face requires well formed arrector pili muscles. Every arrector pili muscle does not have hair attached to them. Arrector pili with hair are found in areas with thick hair. Human facial hairs are extremely tiny and thin. So Goose bump in face is a rare occurrence.