Understanding hair physiology

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Home >> Aspects of Laser treatment >> Physiology of hair
Physiology of hair
Introduction
Hair has a complex structure that is still not fully understood. What we do, however, know is that the hair root is covered in small organs called follicles that have an intricate structure. The follicles are based below the skin surface, which has multiple layers of tissue and three glands whose secretions bathe the hair at many levels along the length of the hair shaft.

Hair has several functions, including heat preservation, and reveals a great deal about a personís physical and mental state. Healthy and shiny hair symbolizes health, youth and vitality. Factors such as illness, a personís diet, hormonal constitution and the shampoos and oils s/he uses, play a major role in determining the texture of hair.

Hair is densest on the human scalp that has between 100,000 to 150,000 hair strands, and grows at a monthly rate of 0.5 inch.

Hair structure
Hair is composed of mainly keratin, a structural protein. Keratin is what the hoofs, furs and feathers of animals are made of. You also find it in the outermost layer of the skin and nails of humans. Cystine, a crystallized pair of molecules of the amino acid cysteine, is among the important ingredients that constitute keratin, accounting for nearly 25% of the protein.

Each hair strand has three layers. Those that are large and thick have a medulla forming their innermost layer. The middle layer, also known as cortex, decides what the texture and color of the hair will be. The third is a protective layer, thin and colorless, and known as the cuticle.

Hair types
There are four types of hair. One, called lanugo, is slender and starts growing during the second trimester of fetal life. The lanugo is usually shed before birth. Infants have short, colorless hair called vellus, which also covers most parts of the human body, except the palms and soles. As we mature the vellus becomes coarser and thicker. When this vellus thickens and gets pigmented we call it terminal hair; it is found on the scalp. However as the hair on the scalp starts to thin, the terminal hair begins to turn into vellus.

Each hair strand consists of a shaft that protrudes above the skin and the root, and is covered by the hair follicle under the skin surface. Yet basically hair is a dead tissue composed of keratin and related proteins.

The purpose of hair
Hair serves several important functions. It conserves heat and protects the scalp against extremes of heat and cold. It also acts as a filter, keeping out the atmospheric filth, that the nose and ear particularly are most vulnerable to. You can wear a hat to fight heat and cold, but what do you do to keep the filth out? These apart, hair is central to the health of the sensory system. The hair follicles, surrounded by sensory nerves, inform the system whenever any pressure is applied on the hair.

Hair-related problems
Baldness is one. It could have genetic origins, or be due to some disease. And while there is no complete cure for it, the condition can be alleviated. Growth of unwanted hair on the body is the second major problem, but one for which there are more satisfying solutions than there are for curing baldness. Several common methods are in vogue, the simplest being shaving. There are also electrolysis and laser hair removal. All these are for women suffering from hirsutism -- the tendency of certain women to have excess hair on the face, the hands, the legs and around the chin.

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