Ryan Gallagher, of St Joseph's School, Port Chalmers, asks :-

What causes the goosebumps I get on cold days?

David Bolton, a physiologist at the Otago University Medical School, responded.

These'goosebumps' are hair follicles, the bits of your skin which house the hairs themselves, trying to erect the hairs in order to enclose a thick layer of air and ward off the cold.

Air is a very good insulator of heat, in fact the reason we wear woolly clothes is to trap air around us and stop it moving away to be replaced by colder drier air. Why drier? Because we lose a lot of heat by evaporation of water from our skin, even when we are not actively sweating. So having warm moist air around us prevents evaporation, as well as the need to warm up more air. Our ancestors had lots of hair, and for them erecting hairs was as good as putting on another jersey. Although most of us now don't have enough hair to make it worthwhile, our bodies' control systems still include this message to the hair follicles, along with changes to the flow of blood to the skin and the desire to find shelter, curl up tight or huddle together with your mates.

You can also get goosebumps if you see or hear something really scary, because the controls that prepare you for fighting or running away may use the same messages as the ones for keeping warm. My cat's fur stands upright when he sees a dog too close, especially the hairs on his tail and along his back; perhaps it makes him look bigger and stronger.