Most people describe their hair as either thick or thin. However, the number of hairs you have can affect the thickness as well as the size if each hair. The diameter of scalp hair does not have a typical size given that different scalps have different hair structures. There are a number of factors that can affect the diameter of hair as can be seen by the examples given below:
The human hair diameter can be so varied that measurements have been known to range from 20 to 180 µm (millionths of a meter).
Commonly hair texture is termed as thin, fine, medium or thick, coarse and wiry. Hair texture can change with the addition of products, chemicals or hair styling.
The texture or feel of hair can depend on a number of factors:
Note: “Weathering” is a term used to describe the progressive deterioration of the hair. Firstly the cuticle layer, then eventually the cortex. This is caused from exposure to continual daily wear and tear.
As well as hair appearance being termed in colour or texture, it can also be referred to as straight, curly, wavy or even frizzy. Hair shape can vary widely in people. What determines the shape of the hair is the shape of the hair follicle and its position in the scalp. This shaping and positioning of the hair follicle is genetically determined. The follicle is fundamental in giving the hair its shape from the moment it is manufactured and, as hair is considerd biologically dead tissue, the hair tends to keep this original shape. This shape is never entirely circular. Curly hair is shaped like an elongated oval and grows at an angle to the scalp. It also has a different biological structure from that of straight hair.
Curly hair is often likely to be dry in comparison to straight hair and tends not to shine. In most cases, the reason for this is the hairs lack of smoothness. Oils present on the hair, secreted by the sebaceous glands, travel down the hair more easily when hair is straight, this helps to keep moisture in and the hair soft and smooth. The smoother the hair, the more it will shine. This is due to the level of light reflected from the surface of the hair. Very curly hair can be dry, often frizzy and difficult to manage. See Hair Care
Atmosphere can affect the moisture content of hair:
The reason why hair changes in different atmospheres is down to the moisture in the air. For example, damp and humid conditions can cause wavy hair to become curlier or even frizz. This is due to the hair increasing in water content and reducing its static electricity content. Curly hair becomes curlier the wetter it gets. When hair is wet, the cuticle scales tend to lift, the cortex can swell and the hair surface temporarily loses its smoothness.
It is also important to note that different hair types have different moisture absorbing abilities, the more Porosity the hair has the more moisture can penetrate it.
Soft, smooth and silky hair is likely to have less porosity than other dry, wiry and rough hair. This is largely due to the cuticle layer of the hair resisting the penetration of the moisture in the air. The hair can also become increasingly porous, such as when it is subjected to chemical processing or damage by external elements. The more porous the hair is the dryer it will feel, as more moisture can penetrate the cortex. If this is the case, more moisture can then be lost leading, ultimately, to weaker hair. Conditioners, of course, can help prevent this moisture loss (see conditioners).
Refers to the hairs ability to stretch and return to its original shape without breaking. The Degree of elasticity in the hair can be measured by how much it is able to be stretched whilst still being able to spring back to its original form without breaking. Due to its incredible elasticity hair can be very resistant. When healthy hair is wet and stretched it can increase in length by up to 30% and still return to its original length when it is dried. However, stretching it more than this can lead to snapping or breaking.
There are a number of factors that can affect the elasticity of hair, the most common of which are mentioned below:
Hair with poor elasticity will stretch only to a limited extent. It can break easily when it is groomed and cannot be styled properly.
In general, strong hair is considered a sign of healthy hair. However, on the whole, hair is remarkably strong and resilient. The key factors in supplying the hair its' strength and durability are the disulphide bonds. The middle layer of the hair, the cortex, is made up of polypeptide chains cross-linked with each other by side bonds. These bonds that link up the polypeptide chains of the hair are disulfide bonds, hydrogen bonds and salt bonds. Below you will find greater detail pertaining to each of these three types of bond:
Salt bonds are also weak physical side bonds that are easily broken by either, weak alkaline or acid solutions and changes in pH. These bonds can be reformed by normalizing the pH level of the hair.
The breaking and altering of these bonds is implemented to change the hair in physical and chemical processes. For example by water as in wetting the hair then drying it in a different shape, this process then re-sets the bonds.
In chemical processing for example, an application of alkaline or acid such as perming. As perms break the bonds then hydrogen peroxide applied will then fix the bonds in the altered form.
Static electricity is the imbalance of positive and negative charges. As hair can act as a conductor static electricity can build up on the hairs and its effect on the hair is best described in the following way:
If an item, such as a woolly hat, rubs against your hair, electrons move from the hair to the hat and a static charge builds up on the hair. As the static charge builds, each of the hairs end up with the same positive charge. Items with the same charge repel each other and, as such, each hair tries to get as far as physically possible from all other surrounding hairs. In order to do this they stand up on end and away from one another. This is how static electricity causes or contributes to a bad hair day! This can also happen whenever the hair is rubbed, brushed or combed, especially when the hair is dry. Subsequently, charged hairs can never lie smoothly against each other. The result is 'fly away' hair which stands out from the head and looks unmanageable.
Static electricity on the hair is commonly noticed more in the winter when the air is dryer. During the summer the air is generally more humid and the water in the air means that less of a static charge builds up on the hair. Shampoos with added conditioning agents, conditioners and some styling products leave the surfaces of the hair smooth. As a result, there is less friction when the hairs are rubbed together, therefore less static electricity builds up on them and the 'fly away' problem is less. Also, many hair products can contain anti-static properties. (See hair products) * set link
Three types of hair grow on the human body
Hair Colour and Pigment
As well as texture, hair is commonly typed according to its colour, for example: someone who is blonde-haired, a red head, a brunette or even if they have mousey hair. The most frequent chemical process that is used on hair is to change its natural colour to something different. There are many different shades of colour that can be applied to the hair ranging from natural colours, used for the covering of grey hair, to radically bright colours used as a styling statement.
The pigment that gives colour to hair and skin is called Melanin. The melanin is produced by an assembly of cells called melanocytes. These cells are present in the hair bulb during the growth phase. Particles within the melanocyte, premelanosome and melanosome produce pigment. The completion of melanin formation occurs when melanosome gives way to melanin granules. The hair gets its colour from two types of melanin that create the variety of hair colours. Eumelanin is brown/black in colour and is the most common type of melanin. This form of melanin gives colour to hair shades from black to brown. Phaeomelanin is reddish-yellow in colour and gives the red, yellow and ginger shades of hair colour. The type and amount of melanin present in an individual is dependent upon their inherited genes.
The factors that determine the colour of hair are:
Greying hair is actually white. The hair whitening process is known as canities. Hair appears grey due to the mixture of pigmented hair and non pigmented (white) hair. The amount of pigment granules in the hair gradually begin to decrease with age. A person typically begins to grey between late twenties and forty years of age. The reason for this is that the cells known as melanocytes begin to slow down production and therefore produce less melanin (pigment). This is part of the natural aging process in humans. It has to be noted, however, that some serious illnesses or emotional conditions may also cause the hair to grey prematurely (See Premature Greying below).
There are some instances when the hair will lose its pigment prematurely. This may occur for a number of reasons
There has been some research to show that greying hair could potentially be reversed (See Grey Hair Today – Gone Tomorrow!)
This describes an inherited condition in which there is no pigment present in the hair and skin, leading to the appearance of very pale skin and white hair.
Vitiligo is an acquired depigmenting disorder due to the destruction of pigment cells called melanocytes. The cause and progression of the condition remains largely unknown, however, autoimmunity remains the most popular theory. This is thought to be the case because of the association of vitiligo with autoimmune thyroid diseases and the increased prevalence of autoantibodies including thyroid autoantibodies.
The Hair follicle is an opening in the skin from which the hair grows. It has a supply of blood vessels; the blood passing though these vessels will nourish the hair.
The hair bulb is situated inside at the base of the follicle, it is from this bulb that the hair shaft is developed.
The dermal papilla, inside the bulb, is the site of production and maintenance of hair growth. Further layers, including the inner and outer root sheath and matrix as shown above, surround the papilla.
The cells continue to produce in the matrix of the follicle, layers develop as a result of continuous cell division, to form the inner and outer root sheath then, ultimately the hair shaft. Together these structures comprise The outer root sheath and The inner root sheath, which contains The Henle layer, Huxley layer, and the cuticle of the inner root sheath.
The emerging hair comprises of layers which are known as the hair cuticle, the hair cortex and the medulla. The
portion of hair above the skins surface is termed the hair shaft. Although this is generally composed of three layers Which are the cuticle, cortex, and medulla. However, the medulla may not be present in all hairs, especially finer ones. The medulla is a layer of loosely connected cells in the centre of the hair. The larger spaces in this layer can influence colour and sheen of the hair.
As the process moves up to the mid follicle region, the dividing cells form a hard protein known as keratin, the formation of these hardening of cells is termed keratinisation. This is the part which is referred to as the hair shaft. Cells in the hair bulb produce colour pigment known as melanin, these cells are termed melanocytes, and these cells are carried into the cortex of the hair shaft.
The main part of a hair is actually dead tissue. However, the bulb of the hair is considerd as a living tissue, and the hair itself can be an insightful indicator of health.
Hair loss and damage can reveal influences, on the body from such instances as systemic disease, dietary changes, hormonal imbalances, skin conditions, genetic impact, medication, and lifestyle issues.
Hair growth begins at the hair bulb within the hair follicle found in the dermis, (the innermost layer of the skin) beneath the epidermis, (the outermost layer of skin). By the time, the hair has emerged from the follicle, the process of cell division and keratinisation is already complete. Therefore, the visible hair is considered as dead tissue.
Hair growth follows a typical cycle.
Hair and its growth are nourished by the blood and are greatly influenced by the composition of the blood in terms of nutrients, hormones, and therapeutic drugs. (See Hair Nutrition)
Hair growth in other areas of the body differs in a number of ways.