Wrinkles and gray hair are visible signs of aging. Unfortunately, these processes are irreversible. And if the first wrinkles scare not so much, the first discovered gray hair is able to bring a woman to panic. At this time in the head make the way thoughts that young years behind and old age comes.
But gray hair can appear at a fairly young age-28-30 years, or even earlier. No matter how far science has gone, full of scientific data on the mechanism of hair graying is still there and gray remains a mystery.
THE STRUCTURE OF THE HAIR
Hair, are appendages of the skin. Being related structures, they have much in common, from the plan of the structure, to the features of growth and development.
The root of the hair is located mainly in the dermal layer (reaches the hypodermic). It is called the hair follicle.
The cellular composition of the follicle is diverse and is a mixture of cells:
- specialized cells: melanocytes (produce melanin pigment), fibroblasts (synthesize collagen, fibronectin), keratinocytes (synthesize keratin), glandular cells-sebocytes (secrete sebum)
- non-specialized: stem cells and progenitor cells
The hair follicle is adjacent to the sweat and sebaceous glands, as well as the muscle that raises the hair. Nutrition and innervation of the whole complex is carried out by connecting the capillaries and nerve endings with the dermal papilla.
The follicle is immersed in a layer of subcutaneous fat. With age, this layer on the skin of the scalp becomes thinner.
Continuous hair growth, or rather its rod, is due to the division of cells sitting on the hyaline basement membrane, which limits the inner part of the follicle from the dermal papilla.
Hair color is determined by the ratio of the two pigments-eumelaninu, which gives brown or black hair, and theomelaninu-grayish and yellow shades.
TWO BASIC TYPES OF GRAY HAIR
- gray hair – they diluted pigment
- truly white hair-they have no pigment
Time the emergence of gray hair and its character in some least depend on genetics, and from external factors.
How is the process of relationship of melanocytes (pigment cells) with the cells of the hair, which determine the pigmentation or graying of hair, recently became a little clearer.
Melanocytes are located in the hair follicle, in the area of the dermal papilla. In embryogenesis, the precursors of melanocytes migrate to the hair follicle from the dermis, concentrate directly over the dermal papilla, actively divide and then turn into Mature, do not divide the pigment manufacturers cells.
According to studies, melanocytes, apparently, migrate to the hair follicle, attracted by chemical signals – chemoattractants. Experiments have shown that hair follicle cells produce substances that attract melanocytes.
As the cells divide in the hair follicle growth zone, melanocytes supply them with melanin pigment. All this continues during the stage of active hair growth (anagen stage). Then comes the catagen, during which the hair follicle atrophies and the hair falls out. Then there is a short period of rest – telogen. After that, the hair follicle enters the next period of growth.
THE LIFE CYCLE OF HAIR
Anagen (growth phase) lasts from two to seven years.
The cells in the follicle divide intensely. Hair growth rate reaches about 1 centimeter per month and varies from season to season (in winter hair grows faster). In this phase actively produces pigment, but with age the process slows down.
Catagen (intermediate phase) lasts a few weeks.
Hair growth stops, the pigment is not formed. The follicle gradually shrinks in size and moves towards the surface of the skin.
Telogen (phase loss, or vacation) lasts in average 3 month.
During this period, the hair may fall spontaneously or as a result of light effort. Independent hair loss occurs, as a rule, when a new hair begins to grow under the old hair.
It follows that the production of melanin in the hair follicle is cyclical, in accordance with the cyclic nature of hair growth, unlike the epidermis, where melanocytes produce pigment continuously.
Graying hair from the roots due to the fact that again formed keratin fibrils of the outer part of the hair for some reason do not get the pigment or get it enough.
CAUSES OF GRAY HAIR
The rapid graying of hair (overnight) many scientists doubt – can not have grown hair suddenly lose pigment, unless, of course, it was not affected by some chemical that destroys melanin.
In the scientific literature, there is a variant of the explanation of this phenomenon: stress causes the loss of pigmented hair, resulting in previously unobtrusive gray hair comes to the fore. But what causes hair to fall out so selectively and how it turns out that people do not notice abundant hair loss that precedes the appearance of gray hair is not explained.
From a scientific point of view, there are incredible stories about the wonderful return of hair color under the influence of cosmetics or food additives. If the color to return, then it should happen gradually, as the hair growth.
It is not yet clear what happens to the pigment cells at the rest stage of the hair. In the research center of the data were obtained that the follicular melanocytes present enzyme tyrosinase. During anagen, this enzyme can be determined, and at the catagen stage tyrosinase can not be detected, although melanocytes are still in the bulb. Also, when a new stage of anagen begins, melanocytes, located near the dermal papilla of the hair follicle, begin to divide. Melanocytes available in other areas of the hair bulb do not react to the beginning of anagen.
Most likely, in the hair follicle, there are two populations of melanocytes: active melanocytes, responsible for pigmentation of hair, and reserve melanocytes, which are activated with each new cycle of hair growth.
Another study showed that Mature hair melanocytes, which enters the catagen stage, are destroyed by undergoing apoptosis (programmed cell suicide). That is, those melanocytes, which supplied the pigment growing hair in the anagen stage, most likely, die at the catagen stage, and pigmentation of the hair in the next growth cycle is due to reserve melanocytes. Where the reservoir of spare melanocytes is located is not yet clear, but it can be assumed that the cells in it may be exposed to harmful environmental influences. This ultraviolet radiation, chemicals, inflammation and others. As a result, defects may accumulate in their genetic apparatus. It is also possible that the supply of melanocytes in the reservoir is limited, which explains the inevitability of hair graying.
In the hair follicle, there is a complete reconstruction pigment manufacturersapproximately 10 cycles of hair growth, which occupy about 40 years. Then the synthesis of the pigment slows down, and the hair gradually discolored-graying.
This occurs due to the depletion of reservoir cells or as a result of violation of synthesis of melanin?
Based on the same data obtained by scientists, melanocytes are found in the hair follicles of white hair, which no longer produce melanin. At the research center of the to identify melanocytes applied the immunohistochemical method. And according to them, melanocytes are found only in gray hair, while in white hair the number of melanocytes or sharply reduced (almost to zero), or melanocytes are absent.
One of the currently existing theories suggests that the reduction of melanin synthesis occurs first by reducing the activity of the key enzyme melanogenesis – tyrosinase. This leads to the appearance of gray hair. Then other factors begin to affect, for example, a violation of the interaction between melanocytes and hair cells, slowing the migration of melanocytes into the hair follicle, deterioration of microcirculation of the hair follicle.
Another possible cause of gray hair – DNA damage melanocytes active oxygen forms formed under the influence of ultraviolet radiation and other factors. This may occur against the background of reduced activity of the antioxidant system of the skin with age. In the end, there is a genetically determined depletion of the reservoir of melanocytes, and the hair becomes white.
CAN SLOW DOWN GRAY HAIR?
These questions scientists are in no hurry to answer “no”. Some experiments have shown that white hair melanocytes are able to produce pigment in vitro in cell culture. In addition, the dependence of graying on external and internal factors, such as circulatory disorders, stress or inflammation, theoretically means that, protecting hair follicles from such effects, you can slow the onset of gray hair.
Until now, it is not clear why there is gray hair. And since science-based methods of dealing with it does not yet exist, various methods of dyeing her hair remains the most reliable method of masking both grey and white hair.