What causes goose bumps?

Goose bumps or goose pimples are little bumps on your skin that appear when you are cold or afraid. They are named that because they look like the bumpy flesh of a goose that has had its feathers plucked. When you are cold the muscles in your skin raise the hairs on your body so that they can trap a thicker layer of air next to your skin, which may keep you a bit warmer. And, as with all muscular activity, this contraction of the skin muscles also produces heat.