Hair is the collection of thin strands that grow from the skin of mammals, including humans. Each strand is made of a protein called keratin, the same material that forms your fingernails. On your head alone, you probably have between 80,000 and 120,000 individual hairs, each growing from its own tiny pocket in your scalp called a follicle.

Hair serves important purposes. It helps regulate body temperature, keeping your head warm in winter like a built-in hat. Your eyebrows keep sweat from dripping into your eyes, while eyelashes protect your eyes from dust. Animals use hair (often called fur or a coat) for warmth, camouflage, and sometimes defense, like a porcupine's sharp quills, which are modified hairs.

Hair grows continuously but at different rates on different parts of your body. Head hair grows about half an inch per month, which is why you need regular haircuts. The color, texture, and curliness of your hair depend on your genetics: some people have straight hair, others have curls or waves, and hair color ranges from black to blond to red.

People often style their hair in different ways, cutting it short or growing it long, braiding it, or arranging it in various fashions. Throughout history and across cultures, hairstyles have signified everything from social status to personal expression.