Hair is the characteristic threadlike outgrowth of the outer layer of the skin of many mammals, forming an animal’s coat or pelage. It serves several purposes: it helps regulate body temperature, provides camouflage or visual signaling (like the polar bear’s white fur), assists in mating and sexual display, and for some mammals, even protects against cold temperatures, snow, and sun. Hair is present to some degree on all mammal species, although it is most prominent on elephants, rhinoceroses, sirenians, and whales.
Hair grows from a small hole in the skin called a follicle. The follicle extends into the dermis and is connected to a blood vessel that supplies the hair with nutrients. The hair is also supported by a special gland that produces sebum, an oily substance that acts as a natural lubricant and prevents the hair from drying out.
The hair is made of a protein known as keratin, which gives it strength and structure. The keratin proteins are packed tightly together in a helix formation, and they are covered by a thin layer of lipids that makes the hair shiny. The helix is surrounded by the cuticle, cortex, and medulla. The medulla is a honeycomb-like region in the center of the hair that contains melanocytes, the cells that produce the pigment that determines the color of the hair.
For humans, our hair serves mostly as a form of protection. It is thicker on the head than on other parts of the body, providing a barrier that protects the brain and the scalp from UV rays that could cause sunburn. In addition, hair can provide a tactile signal to others, making it easier for people to recognize each other.
In some cultures, hair is seen as a sign of beauty or femininity. In Ancient Egypt, for example, a woman’s hairstyle was considered an indicator of her rank within the hierarchy. In modern times, women who are balding or with very sparse hair may still choose to wear their hair in a certain style to express a sense of femininity, and the popularity of certain hairstyles has served as a way to distinguish one group from another, such as when Oliver Cromwell’s followers cropped their hair short during the English Civil War, turning them into a band of Roundheads.
However, for those with voluminous hair, keeping it healthy and shiny isn’t always easy. To keep their tresses looking their best, those with thick hair should look for shampoos that are free of silicones, which build up on the hair and make it dull and dry. They should also avoid products that contain alcohols, as they can lead to dryness and breakage. Instead, those with thick hair should opt for shampoos that are rich in moisture-boosting ingredients, such as argan oil (derived from the nuts of the Argania spinosa tree) and shea butter.