They will show themselves when you are frightened, or when you’re shivering from the cold. Sometimes they can appear at the slightest touch. If the area in which they appear is particularly hairy, the hair follicles can stand completely on end. If you’re not expecting it, it can be a strange sensation. But why do they appear? What’s the biology behind goosebumps?
Why Do We Have Goosebumps?
The short and simple answer is that goosebumps are a remnant of our hairy past. They are an evolutionary feature.
The longer answer is that at one point, we were all pretty hairy. Completely hairy in fact. While most of us have lost the bulk of our body hair, the internal wiring is still present. The evidence of this internal wiring is the goosebumps themselves (some people call them goosepimples).
Goosebumps are an automatic reaction of our nervous system. The nervous system activates them by flexing the piloerector muscle found at the base of every hair follicle. Piloerector literally means “making the hair stand on end”. This reaction is triggered by the nervous system for one of two things — either you are very cold, or you are frightened out of your wits.
Using Cats As An Example
Looking at cats, or just about anything else more furry than us, animals can puff up their fur (or hair) when they are cold to trap and hold more air around their body. By trapping air near their body, they are creating a small pocket warm air which insulates them and keeps them warmer than without. When our goosebumps are triggered, they are attempting to do the same thing.
As for being spooked or scared, the fur puffing reaction is seen in many animals (including cats) as an attempt to make themselves appear larger and more threatening than they are. The general rule of thumb in the animal kingdom is that size generally equals power. So whenever an animal has the capacity to make itself larger, it stands a better chance of scaring away whatever may be attacking or harassing it.
Fun Fact: Even though we call them “goose” bumps, only mammals have what is known as “horripilation” (the scientific term for goose bumps). Although most species of birds do have a similar system in place, they do not have hair, and thus also lack those small muscles, which lay below the skin level.