Hair is a specialized filament that grows from follicles in the skin. It is one of the most recognizable characteristics of mammals, and it serves a number of functions.
It helps to insulate the body, protect the scalp from cold environments, and regulate temperature by trapping air close to the skin. It also protects the head from sunburn, by reflecting UV radiation away from the head. It can also serve as a social marker, denoting a person’s racial or cultural group.
Humans have many different types of hair, and each type of hair has specific needs. For example, curly hair often requires special care to keep it hydrated and healthy. This can be done with specialized shampoos that target curl patterns and thick hair strands, as well as conditioners that contain intense ingredients such as shea butter, coconut oil, glycerin, and ceramides. This hair type can be difficult to manage, but it can also be beautiful when properly cared for.
The defining characteristic of hair is its elongated structure that extends from the dermis of the skin, and it has a keratin composition. In cross section, a typical hair is composed of three zones: the cuticle, cortex, and medulla. The cuticle is a hard layer of flat keratinocytes that overlap each other like shingles on a roof, and it is covered with a thin layer of lipids, which increases its ability to repel water.
The cortex contains a coiled-coil protein phase and intermediate filaments that organize into large fibrils, and it is surrounded by the cell membrane complex. X-ray diffraction of human hair shows a lamellar periodicity and rings at spacings of about 4.3 A, which is due to the lipid order within the membrane layers.
Although it is not clear when humans first acquired body hair, it has been suggested that it may have evolved as a response to the harsh African environment. Specifically, it is believed that hair was necessary to protect the head and scalp from the intense sunlight of equatorial Africa, which would cause sunburn and skin damage in people without it. The presence of body hair in other mammals provides further support for this theory. However, a recent study suggests that the evolutionary advantage of hair is not limited to ultraviolet protection, as it has many other roles. For example, it is thought that hair in the chest and groin provides thermal regulation, and it also plays a role in sexual behavior in females. Interestingly, it is also thought that the hairs on the arms and legs are used to signal a male’s readiness for mating. Despite these various functions, some experts believe that the use of hair for social or aesthetic reasons has become more important than its functional role. This has led to the development of many products designed to protect, style, and treat hair. Many of these include shampoos, conditioners, and sulfate-free hair treatments that contain vitamins and minerals. In addition, there are a number of techniques that are used to modify the appearance of the hair by cutting, curling, dyeing, and bleaching.