In prehistoric times, goose bumps may have helped humans frighten their enemies. Now they’re not much use. The hairs on your body lie close to your skin and have small muscles attached to them called arectores pilorum. When you feel cold or are frightened, these muscles pull on the hairs so they stand out almost perpendicular to your body, causing small bumps to appear. Hairs trap air between them in the same way that the fibers in a sweater trap air, helping to keep you warm. The arectores pilorum muscles also press against the oil glands located at the base of each hair shaft and squeeze oil onto the surface of the skin. The oil covers the skin’s surface and helps to keep the skin warm by reducing evaporation of sweat from the skin’s surface.

Many thousands of years ago, people had more body hair and fewer clothes. Contraction of arectores pilorum muscles caused hair to stand on end, making a man appear larger than he was. Today, our greatest adversaries are other people, and goose bumps may reveal that you are scared. Now most people hide their goosebumps with clothes.

December 10, 2005