What Is Hair

Hair at its most basic form is a biomaterial which is very thing. It is generally found in the skin (dermis). Almost the entire human body is covered in hair apart from glabrous skin areas (such as the palm of the hand). The hair is produced in hair follicles, these follicles produce two types of hair thin vellus hair "bum fluff" (this is prevalent when young over the body), then there is the dense terminal hair (adult hair, mostly obviously found on the head). Generally hair is a very important topic to many people, given its interlinking with beauty and perceived attractiveness. Whether it be male hair loss or female over growth of hair, a huge industry surrounds hair. Hair is produced in hair follicles deep in the skin. It is the only body structure that is renewable without scarring. In the developing fetus the hair follicles form by week 22. At this point there are 5 million follicles present. 1 million of these in the head, and this is the largest number of follicles that we will have, as new follicles are not added during life, as we age the thickness of the follicles reduces.

Hair is mostly made from protein. Its principle component is keratin (keratins are long chains of amino acids). Human hair comes in four main shades; black, brunette, blonde and red. Hair is normally split into two distinct structures, there is a section beneath the skin, this is called the hair follicle, and when a pulled from the skin it is referred to as the bulb. he hair follicle contains stem cells which are used to regrow hair and to regrow skin after a cut has occurred on the skin. The part which protrudes from the dermis is called the shaft. Hair is between 17 to 180 µm in width. The average human head has about 100,000 hair follicles. It is normal to lose about 50-100 hairs from the head each day.

When looking at the cross section of a hair there are three distinct zones:

  • The cuticle - this is the outer most layer and consists of a few layers of flat cells which overlap like shingles.
  • The cortex - this contains groupings of keratin in cell like structures
  • The medulla - this is the innermost section and is generally not organized (it is also not always present)

Creation of the hair

The Keratin withing the hair is arranged into filaments. The structure gives the hair its tensile strength. The visible part of the hair starts its life inside the hair follicle. In fact the only part that is classed as living is the follicle, the rest is effectively dead as it has not activity. Within the hair follicle there is also the sebaceous gland. drawing of a hair follicle The sebaceous gland produces oil which oils the hair. Also there is the erector pili muscles. These muscles have the arduous job of getting the hairs to stand up on end, as a heat conservation mechanism. These produce the goose bump effect. Interestingly enough this reaction can trigger in other situations which have nothing to do with heat conservation. The cortex part of the hair is where the melanin is stored. The melanin is what gives the hair its pigment. The various different colours are achieved by the number and mixture of these granules, there are two separate types of melanin pigment found. To get darker hair Eumelanin must dominate, while to get red hair it is required that pheonmelanin be most prevalent. Blonde hair is actually produced by having very little pigment. The arrangement of the fibers determines how straight or bendy the hair is. Older people will tend to get grey hair because the pigment which colors the hair is lost. In general everyone over the age of 75 has grey hair.

Hair Growth

Hair has a very specific cycle. There is the anagen, catagen and telogen phases. The phases are in no way coordinated across hairs, so some hairs are in anagen, some are in catagen and some are in telogen.

The function of hair

Hair has various functions in humans

Hair keeps us warm. Although hair is not as thick as fur on other mammals, in humans it does help to keep the head warm, which is very important as a large portion of heat loss which occurs in humans is from the head. Hair also helps to cool humans down via the mechanism of sweating.

Hair helps to protect humans, although not as impressive as porcupines, the hair on humans helps to keep the senses at full power. The most obvious example would be eye brows and eye lashes which help to keep debris out of the eye.

Hair helps us to sense touch quicker, as movements of the hairs are felt by nerve receptors which are nearby the hair follicle. This is so sensitive that even air motion have been sensed. This is heightened in certain areas such as eye lashes where it is essential that the response be immediate.

Grooming practices

Hair removal is a constant endeavor because of the ever growing nature of hair in most respected. Almost always hair removal is done due to it being perceived to be better looking. Two terms which are commonly used to do with this is depilation, which is the process of removing the visible hair strand (by shaving for example) while Epilation is the removal of the entire hair including the hair strand which is still within the follicle.

Shaving is the most common way to get rid of hair and is mostly mandatory for men. The basic concept is to bring a sharp blade close to the skin and cut the hair as close to the skin as possible. Remarkably hair begins to grow out almost immediately. The hairs that appear are referred to as stubble and tend to look more obvious, but this is not because more hair is growing rather it is because the ends of the hair tend to be the thinnest whilst the base is the thickest.

Waxing is the process of sticking wax to a cloth and removing the hair using a sharp motion. This technique tends to last longer that shaving, and it can generally take the hair up to 9 weeks to come back again to the surface.

Cutting and trimming is most commonly done on the head, this is achieved with clippers or scissors.

Laser hair removal and Electrolysis are two examples of methods to permanently stop the hair from growing back, by destroying the hair follicle