I bet the AC in your office has given you a fair share of goosebumps. Want to know what causes them? Scientifically speaking, they're triggered by a reflex called piloerection. This reflex causes tiny muscles at the base of each hair to contract, making the little hairs that cover your body to stand up. Which in turn makes little bumps all over your skin, giving it the appearance of a freshly-plucked goose.
When animals get cold, this reflex helps to fluff up their hair or feathers to trap in body heat. Human goosebumps on the other hand are an attempt to make us warm, but since we have such little body hair, goosebumps serve absolutely no purpose.
Goosebumps are also a physical response to fear, just like when you sweat or your heart races. When animals are scared, like a cat or porcupine, they get goosebumps too and their fur or quills stand up, making them look more fierce. Our tiny hairs stand up, too, but I think we can all agree that it doesn't do much to protect us from harm or make us look more ferocious.
Our skin also gets all goosebumpy when we hear beautiful music or a touching story. Like other emotion-linked reflexes such as blushing, turning pale, and butterflies in your tummy, goosebumps are triggered by the limbic system of the brain. This bodily response isn't driven by a physical prompt, but by a psychological one. Yet another example of the mind-body connection. Wow. I just gave myself goosebumps.