The scalp is nothing but the skin on the head. The skin of the scalp is exactly similar to the skin on any other body part. The part of the hair we see above is dead, the actual living part is very small which is knows as root of the hair which exists in the part known as the papilla. In the papilla, cells multiply and produce a protein called keratin - this is responsible for the hardness of the hair.
The part of the hair which is within the skin, is enclosed by a sleeve of tissue called the follicle. Next to each follicle is a sebaceous gland - the oil producing gland of our skin. This oil forms a natural protective film over the length of hair, keeping it soft, supple and look shiny.
The chemical composition of hair is:
Carbon : 50.56%
The chemical composition of hair varies from person to person. It also depends on the colour of the hair.
Hair is composed of three layers:
The medulla is the innermost layer of hair. It is absent in very fine hair.
The cortex or the middle layer contains the color pigment granules that provide color to hair. The colour of hair depends on the number, size and distribution of the pigment granules in the cortex and also on the nature of pigment present. Colorants and bleaches work by penetrating the cuticle so that the colour is added to or subtracted from the cortex.
The cuticle or the outer most layer is composed of overlapping cells that resemble shingles on a roof. It has tiny overlapping transparent scales. When the scales lie flat against each other, the hair appears shiny, does not tangle easily, but when the scales are lifted, hair seems rough and dull. Conditioning rinses help to keep the scales positioned correctly, giving it a smooth and shiny appearance.
The cuticle of the hair is selectively porous. This porousness varies along the length of the hair, the bit nearest to the scalp is the least porous. Oily hair is less porous than dry hair. The porous nature of hair allows for the penetration of chemicals. The agents used in bleaches, tints and perms capitalize on this nature of the hair - the chemicals used are quickly absorbed and bring about the necessary changes in colour and curliness.
The cuticle gets damaged easily. The cuticle can get damaged due to many reasons:
Because of any or all of these factors, some of the cuticular cells begin to separate and may even get torn off. The surface of the hair now begins to look rough and scarred. The hair tangles more easily. It looks dull and drab. The ends may fray and split into layers (split ends). Such hair if we talk in technical terms are called 'weathered' hair.
Weathered hair is rough, dry, brittle, porous, breaks easily, lighter in colour and develops split ends. Since the hair shaft is dead, once hair has been damaged it cannot repair itself. Hence the damage is permanent, and to have shiny, easy-to-manage hair once again, you have to wait for new, undamaged hair growth to appear.
Growth of Hair
Full grown hair is divided into two parts: the root and the shaft. The rate of hair growth varies from person to person. The average growth of hair for a normal person (i.e. not suffering from any hair trouble) is approximately 1/4 inch per month, ie., 1/16 inch per week.
The hair growth is mainly fast between the ages group of 15 to 30. Hair growth is faster in summer than in winter. The growth of hair is cyclical, i.e., after a few years of growth, the hair enters a phase of inactivity, then dies and falls. A hair dies when its bulb is separated from the papilla that feeds it. The hair bulb is a thickened club-shaped structure forming the lower part of the hair root. The lower part of the hair bulb is hollowed out to fit over and cover the hair papilla. The papilla is a small cone-shaped elevation found at the bottom of the hair follicle that fits into the hair bulb. Within the papilla is a rich blood and nerve supply, which helps in the growth and regeneration of the hair. Through the papilla, the nourishment reaches the hair bulb.
The hair growth is rapid between the age group of 15 and 30, but declines drastically between the ages 50 and 60. Scalp hair grows faster in women than in men. A certain amount of hair is shed daily. The average amount of 50 to 80 hairs shedding daily is normal. Hair loss beyond this estimated average indicates some scalp or hair trouble. Eyebrow hair and eyelashes are replaced every 4 to 5 months.
The average life of a hair ranges from 2 to 4 years. Factors such as sex, age, type of hair, heredity and health affect the
duration of its life. The average area of a head is about 420 square
inches and there is an average of 10,000 hair per square inch. The
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