Many mammals have hair that serves many purposes. It provides thermal regulation, camouflage, warnings, and sensory experiences. Hair in the nose, ears, and on the head protects from dust and dirt. Eyebrow hairs protect the eyes by trapping particles and sweat. Some animals have hair in various styles, from a simple bob to a complex hat. Hair on the head and neck is especially important for polar bears. They use their fur to keep warm and also use it as a camouflage, especially in icy climates.
Under a microscope, hair appears as a thick tube. The filament is made up mainly of the strong protein keratin. Keratin is also the main component of skin and nails. Hair follicles contain hair bulbs, which are filled with hair cells. These cells receive nourishment from blood vessels. The hair bulb produces new hair cells and replaces the old ones. This is how new hair strands appear. This process occurs repeatedly, so the hair is able to regenerate without scarring.
Your hair color usually correlates with your skin tone. For instance, most blondes have light-skinned parents and darker-skinned people have dark-colored hair. Your hair type is determined by the shape of your hair follicles. Some follicles produce hair that is straight, while others produce curls and flat hair. Genetics and environment play a big role in hair color and shape. Whether you have curly or flat hair is largely determined by your genes, although it does vary throughout your life.
Some hairstyles have deep cultural associations. For example, the early modern Chinese wore a queue, a hairstyle that mimicked male-pattern baldness. This hairstyle was also popular among Han Chinese during the Qing dynasty. During this period, the hair in the front of the head was shaved every ten days, mimicking male-pattern baldness. This hair was then braided into a long pigtail.
Hair growth cycles depend on where you have it. Some areas of the head are in this growth phase for many years. If you let the hair grow uncut, it will grow to over one meter. Ear and nasal hairs grow in less time, but eyelashes and eyebrows only grow 100 days or so. Those who have long lashes are probably in their growth phase. If your hair has grown long, you may be tempted to cut them.
Hair growth and loss cycles are closely linked. Hair follicles have cycles of active and dormant growth. Inactive hair follicles go through the cycle in one month or less, while active follicles stay on for years. During active cycles, about 50 to 100 hairs fall out each day. New hairs replace the older ones. This cycle helps maintain a proper balance of hairs on the head.
The roots of hair follicles are surrounded by tiny blood vessels that nourish the hair root. They are located in the germinal matrix, a rounded structure deep in the skin. The bulb contains several types of stem cells. These cells divide every 23 to 72 hours. Their division rate is faster than other cells in the body. Hair follicles are often sensitive to drafts. Hair grows and renews in the hair bulb.