Your smooth, glossy hairs have a more complicated structure than you might think. Each one can be compared to a tree: all its moisture lies in its centre, behind a tough outer layer of protective bark. If the 'bark' of the hair is well looked after the whole hair remains in good condition. If the 'bark' is stripped off to expose the centre the hair may break.
The centre part of the hair, called the cortex, makes up most of the hair shaft. It is the cortex that gives hair its special qualities such as elasticity and curl. The cortex is packed with strands of keratin, lying along the length of the hair. These keratin fibres are made of the low-sulphur keratins, and are compressed into bundles of larger fibres. These are held together by a mass of sulphur-rich keratins, the matrix. The fibre-matrix combination is extremely strong and resists stretching and other strains such as twisting, much as does the glass fibre-resin mixture from which many boats are built.
The cortex also contains granules of the hair pigment melanin, produced when the hair was growing in its follicle. The granules are of two types: smooth, dark granules which tend to be regularly positioned within the cortex, and lighter granules that are more irregular in shape and which are scattered randomly through the cortex. A hair may contain just one type of granule or a mixture.
In some of the terminal hairs, especially grey (unpigmented) ones, the cortex has a central hollow core, the medulla. There are medullae in the hairs of many animals, and they play a part in the regulation of body temperature. It may be that the presence of this air space in some human hairs is an evolutionary 'throw-back' to a time when our ancestors needed extra heat insulation.
The outer layer of the hair (the 'bark') is called the cuticle. It is made up of between six and ten overlapping layers of long cells. Each of these cells or scales is about 0.3 micrometres thick and around 100 micrometres long, and about 10 micrometres across. (1 micrometre, written 1 µm, is one-millionth part of a metre = one-thousandth part of a millimetre.) The scales lie along the surface of the hair like tiles on a roof, with their free edges directed towards the tip. They cover the hair surface all the way along its length.
If you could look at a hair under a powerful microscope you would see that the scales growing over the youngest part of the hair (the part that grows closest to the scalp) are smooth and unbroken. Further along the hair, you would be able to see that they may have been damaged by cosmetic treatments and by mistreatment such as over-energetic brushing. Little by little they may break away, a process called weathering.
A healthy cuticle is more than just a protective layer. Much of the shine that makes healthy hair so attractive is due to the cuticle. Intact cuticle cells are smooth and glossy, and reflect light from their surfaces. This, together with the pigment within the cortex, gives hair its characteristic appearance.
Black hair reflects less light than blond hair does. Black hair appears glossier, however, Because the bright bands of reflected light contrast more sharply with the darkness of the rest of the hair.
The centre part of the hair, called the cortex, makes up most of the hair shaft. It is the cortex that gives hair its special qualities such as elasticity and curl. The cortex is packed with strands of keratin, lying along the length of the hair. These keratin fibres are made of the low-sulphur keratins, and are compressed into bundles of larger fibres. These are held together by a mass of sulphur-rich keratins, the matrix. The fibre-matrix combination is extremely strong and resists stretching and other strains such as twisting, much as does the glass fibre-resin mixture from which many boats are built.
The cortex also contains granules of the hair pigment melanin, produced when the hair was growing in its follicle. The granules are of two types: smooth, dark granules which tend to be regularly positioned within the cortex, and lighter granules that are more irregular in shape and which are scattered randomly through the cortex. A hair may contain just one type of granule or a mixture.
In some of the terminal hairs, especially grey (unpigmented) ones, the cortex has a central hollow core, the medulla. There are medullae in the hairs of many animals, and they play a part in the regulation of body temperature. It may be that the presence of this air space in some human hairs is an evolutionary 'throw-back' to a time when our ancestors needed extra heat insulation.
The outer layer of the hair (the 'bark') is called the cuticle. It is made up of between six and ten overlapping layers of long cells. Each of these cells or scales is about 0.3 micrometres thick and around 100 micrometres long, and about 10 micrometres across. (1 micrometre, written 1 µm, is one-millionth part of a metre = one-thousandth part of a millimetre.) The scales lie along the surface of the hair like tiles on a roof, with their free edges directed towards the tip. They cover the hair surface all the way along its length.
If you could look at a hair under a powerful microscope you would see that the scales growing over the youngest part of the hair (the part that grows closest to the scalp) are smooth and unbroken. Further along the hair, you would be able to see that they may have been damaged by cosmetic treatments and by mistreatment such as over-energetic brushing. Little by little they may break away, a process called weathering.
A healthy cuticle is more than just a protective layer. Much of the shine that makes healthy hair so attractive is due to the cuticle. Intact cuticle cells are smooth and glossy, and reflect light from their surfaces. This, together with the pigment within the cortex, gives hair its characteristic appearance.
Black hair reflects less light than blond hair does. Black hair appears glossier, however, Because the bright bands of reflected light contrast more sharply with the darkness of the rest of the hair.