Life cycle, growth rate and depth of hair in various parts of the human body. The structure, functions and phases of hair growth What is the anagen phase

Hair is very important for a person, and not only for biological, but also for cosmetic and aesthetic reasons, hair allows you to emphasize the image of a person, make him more attractive and attract the attention of the opposite sex. Many writers describe the beauty of women's hair and its magic. After all, it is not in vain that they say that a woman without beautifully styled hair is like a picture without a frame.

Hair covers almost the entire human body and performs the following functions:

protect the body from the harmful effects of the environment and mechanical influences;
participate in thermoregulation (maintain the temperature balance of the body);
are organs of touch, as they are surrounded by the finest nerve endings.

The approximate chemical composition of a healthy hair is as follows:

15% water
6% lipids,
1% pigment,
78% protein.

Hair structure: outer and inner part

Conventionally, each hair can be divided into 2 parts: the shaft (trunk) and the root. Kernel- this is the visible part of the hair, protruding above the surface of the skin and growing from the hair follicles. The hair root is located in the skin layer and is surrounded by the root sheath. Together they are called hair follicle.

The hair shaft can be located at different angles relative to the surface in a wide range: from 10 to 90 degrees. A small angle of growth (~10-20 degrees) can sometimes create problems in creating hairstyles, since it is difficult to style the hair in the opposite, unnatural direction for them. Also, with such a small angle of growth, it is possible for hair to grow into the skin, which causes inflammation.

The outer part of the hair has three layers:

The core (inner part) contains non-keratinized cells.
The cortex (cortical layer) makes up 90% of the mass of the hair. Consists of elongated cells. It is here that melanin is contained, which is responsible for hair color.
The cuticle (outer layer) in structure resembles cone scales or tiles, where each next part slightly coincides in area with the previous one.

Other structures adjoin the hair follicle: the sebaceous gland, the sweat gland, and the muscle that raises the hair (thanks to which the expression “hair stood on end” exists). In addition, the hair follicle is well supplied with blood vessels. In men prone to baldness, the vascular apparatus of the hair follicle has an increased sensitivity to hormones (androgens): dihydrotestosterone and the enzyme 5-alpha reductase, which converts testosterone to dihydrotestosterone. During puberty, when the amount of androgens in the blood is increased, the vessels of the follicle steadfastly spasm, the nutrition of the hair follicle is disturbed, and, as a result, baldness occurs (even Hippocrates said that eunuchs do not go bald). It is important to note that only the hair of certain areas of the head has such increased sensitivity to androgens, but not all hair on the human body.

The hair follicle is a receptacle for the hair root, which is also called the bulb. Bulb- this is a small thickening and consists of cells that are intensively dividing, form a hair. The bulb has an unusual immune status, the violation of which, presumably, is one of the causes of alopecia areata.

In the lower part adjoins the bulb hair papilla which contains blood vessels. The hair papilla is a very important component of the follicle, as it controls the condition and growth of the hair. If the papilla dies, then the hair dies. However, if for any reason the hair dies (for example, it is uprooted), and the papilla is preserved, then a new hair will grow in its place.

hair follicle is a complex structure that is in constant cyclic development: the stages of anagen, catagen and telogen.

hair growth stages

Anagen- the period of active hair growth. Last an average of 2-6 years. With age, the duration of the anagen phase decreases. The anagen growth phase is also divided into 6 stages:
Hair bulb cells increase in size, intensive RNA synthesis occurs.
The hair bulb grows downward in the epidermis and practically surrounds the dermal papilla. Cell differentiation begins into different layers of the hair and the outer shell of the root in the matrix ring that surrounds the dermal papilla.
Cell division continues. By this time, the hair follicle has reached its maximum length, which is 3 times longer than in the resting phase. The dermal papilla is also fully developed. Melanocytes (epidermal cells that are responsible for the production of melanin, which gives hair a certain color) are located along the cavity of the papilla, each of which (each of the melanocytes) forms melanin granules. The outer shell of the follicle cavity is now an elongated cone that expands from above.
At this stage, melanocytes begin to produce melanin (pigment). Although the hair is already formed, it still does not extend beyond the boundaries of the cone-shaped cavity, which continues to expand.
The hair grows to the upper border of the epidermis, the bulb acquires a finished shape, which in some hairs is symmetrically rounded, in others it is squeezed like an ellipse.
The last stage begins as soon as the hair begins to rise above the skin and continues until the catagen phase. In anagen stage 6 mice, hair grows at a rate of 1 mm per day. In humans, this stage lasts from 2 years or more. Hair is produced at a rate of 0.5 mm per day.

Catagen- the period of transition from one stage to another. In the catagen stage, atrophy of the hair papilla begins, as a result of which the cells of the hair bulb, deprived of nutrition, stop dividing and undergo keratinization. This stage lasts only a few weeks, after which a short telogen stage begins, which smoothly passes into the developmental stage.

Telogen- a period of rest or rest of the hair. Interestingly, the mechanical removal of hair in the telogen stage always entails the onset of the anagen stage, that is, the hair begins to grow again. All hair that remains on the brush or falls out during the day is telogen hair.

Typically, in healthy individuals, approximately 80-90% of the hair is in the anagen stage, 1-2% is in the catagen stage, and 10-15% is in the telogen stage. Studies show that excessive hair loss corresponds to a change in the above ratio: the percentage of hair in anagen and catagen decreases, but the percentage of telogen hair increases. If you notice that the amount of hair falling out during the day has increased dramatically, then know that this is the first sign of a deterioration in the condition of your hair. In people who are not prone to baldness, each new hair does not differ in thickness, potential length and other characteristics from the previous ones; at the same time, in balding, each new generation of hair decreases in thickness, color (lightens), the growth rate and duration of the anagen phase decrease. Ultimately, healthy hair gradually degrades to vellus and colorless hair.

Distribution of hair on the body of men and women

Man with pronounced body hair

Hair removal, also known as "epilation" or "depilation" is the removal of body hair. The term is applied to the methods of achieving a given result.

Many products on the market turn out to be fake, exaggerating results or ease of use.

Kinds:

depilation- hair removal above the skin surface. The most common type of depilation is shaving or cutting. Another option is to use chemical depilators, which work by breaking the disulfide bonds that connect the protein chains that give hair its strength.

epilation- this is the removal of the entire hair, including the part that is under the skin.

Hair growth phases

The process of hair growth is cyclical and continues throughout our lives. Hair grows continuously. It has been established that during the day they grow faster than at night, and in summer and winter their growth slows down. The average hair growth rate in children is 13 mm per month, in adults 15 mm and in the elderly 11 mm.

The full development cycle of a fully formed hair consists of three phases: anagen, catagen and telogen.

Anagen- phase of active growth. The duration of this phase is genetically determined and lasts from two to five years. The cells of the hair follicle are intensively dividing.

Catagen- the intermediate phase lasts several weeks. Hair growth in the follicle stops, the pigment is no longer formed, the follicle shrinks, and its base moves towards the skin surface.

Telogen- rest or dropout phase. In this phase, the hair may spontaneously fall out or be removed with a slight effort. The duration of the phase is on average 3 months. The hair falls out at the moment when a new hair begins to grow under it.

According to studies, it is best to remove hair by depilation in the middle of the menstrual cycle in women, when hair growth is 2 times slower.

Hair removal methods

Temporary hair removal at skin level (depilation) lasts from several hours to several days and can be achieved with:

Shaving (manually or with an electric razor);
Depilators (creams or "shaving powders" that chemically dissolve hair)
Friction (rough surfaces are used).

Epilation, or hair removal from the roots, lasts from several days to several weeks, and can be done by:

Permanent hair removal (electrolysis)

For over 130 years, electrolysis has been popular in the United States. It is FDA approved. This method permanently destroys the germ cells responsible for hair growth by inserting a thin probe into the hair follicle and applying a current tailored to each type of hair and treating the area. Electrolysis is recognized by the FDA as the only permanent way to remove hair.

Permanent hair reduction (laser and other types of light hair removal)

(laser diodes and lasers);
(high energy lamps or IPL) or more commonly the method is called ;
(IPL/any laser)
Diode hair removal (high energy LEDs, but not laser diodes)

Experimental or ineffective methods

Methods with unproven effectiveness

Many methods have been proposed or sold without published clinical evidence.

Electric tweezers
Transdermal electrolysis
Percutaneous hair removal
Photoepilation
Microwave hair removal;
Nutritional supplements;
Topical over-the-counter drugs (also called "hair retarders", "hair inhibitors", or "hair growth inhibitors").

Efficiency comparison

In 2006, a review article was published in the journal Lasers in Medical Science, where researchers compared intense pulsed light (IPL), alexandrite, and diode lasers. The review found no statistical difference in efficacy, but a higher incidence of side effects with diode laser. Hair reduction after 6 months was 68.75 for alexandrite laser, 71.71 for diode lasers, and 66.96 for IPL. Side effects were reported at 9.5 for the alexandrite laser, 28.9 for the diode, and 15.3 for the IPL. All side effects were temporary, even skin pigmentation was eliminated within 6 months.

Advantages and disadvantages

There are several drawbacks to many of the aforementioned hair removal methods. The main ones are: skin inflammations, burns, rashes, scars, ingrown hairs, and infected hair follicles. One issue that can be considered both a disadvantage and an advantage, depending on the individual's point of view, is that hair removal has the effect of removing information about a person's hair growth type due to genetic predisposition, disease, androgen levels (e.g. due to for hormonal imbalances during puberty or side effects of medications), and/or gender status.

Another disadvantage of permanent (laser, electrolysis) hair removal is the reduction in the ability of human skin to regenerate, since the hair follicles contain stem cells that help with healing.

Cultural and gender aspects

The hairline is usually present on the entire human body, during puberty the hair thickens and changes color to a darker one. As a rule, men have more visible body hair than women. Both men and women have visible hair on the head, eyebrows, eyelashes, armpits, pubic area, arms and legs, men also have thicker hair on the face, abdomen, back and chest. Hair usually does not grow on the lips, the inside of the arm or leg, or on certain parts of the genitals.

Each culture of human society has its own social norms regarding the presence or absence of body hair, which have changed from one generation to another.

The practice of hair removal in almost all cultures dates back to Paleolithic times. Removal methods and locations have varied over time and culture, but shaving remains the most popular method. Different standards have taken place in both women's and men's fashion. People who did not adhere to the aesthetic norms of society faced real or imaginary problems in society. In the Middle East, the removal of hair from the female body has been considered proper hygiene, due to local customs, for many centuries.

With the increasing popularity of revealing clothing (swimsuits, tops, shorts, etc.), body hair removal (legs, armpits, etc.) has also increased in popularity. In the US, the vast majority of women regularly shave their legs and underarms, while about half also shave their bikini line.

Most people remove their pubic hair for aesthetic or sexual reasons. However, some Western women fundamentally do not shave their hair from open places in order to protest the imposed patterns and aesthetic rules on society.

Men are forced to shave their faces every day also for the purposes of aesthetic norms and rules. However, some men shave their beards because their beard color is different from their hair color, or because their facial hair grows in different directions, making it difficult to look well-groomed.

Alopecia in dermatology is called hair loss. This phenomenon can be due to various reasons, therefore, several varieties of this pathology are distinguished.

Hair growth phases

To understand the causes of anagen alopecia, you must first understand how hair grows.

Hair growth is not continuous, but a cyclical process that continues until the end of a person's life.

The life cycle of a hair can be divided into several stages. Each hair goes through several stages of the life cycle from its inception to natural loss.

The growth phase is anagen. This is the period in which the formation of a new hair and its most active growth. This stage of hair life lasts 2-4 years. During anagen, the hair grows intensively, due to the accelerated process of cell division of the hair follicle.
The intermediate phase is kanagen. This is the dormant period in the life of the hair. During kanagen, hair follicle cells still continue to divide, but at a much lower intensity. At this stage, hair growth practically stops, and the formation of pigment also stops. This phase of the cycle is quite short, it lasts an average of 3 weeks.
The resting phase of the follicle is telogen. This is the period in which the hair may fall out spontaneously or with light mechanical force, such as combing. Natural hair loss occurs when a new root has formed in the follicle and started growing. This phase lasts about 3 months, and it is customary to distinguish early and late telogen.

After natural hair loss, the anagen phase begins again for this hair follicle, and hair growth resumes. Depending on which growth phase intensive hair loss occurs, anagen and are distinguished.

Reasons for development

Anagenic alopecia is the sudden loss of hair during the growth phase. This condition is caused by the influence of negative factors on the cells of the hair follicles. In anagen alopecia, intense hair loss is observed in the growth phase, without transition to the resting phase. Anagenic alopecia is also common, as are the following similar hair diseases: alopecia areata.

The causes of anagen alopecia, as a rule, are the following suppressor factors:

radioactive exposure;
Taking cytostatics and other chemotherapy drugs in the treatment of and other diseases;
Taking hormonal drugs.

In addition, active hair loss in the anagen phase can be triggered by:

Severe somatic diseases;
In infectious diseases, especially those accompanied by prolonged fever;
During pregnancy;
With prolonged fasting, including long-term adherence to a rigid unbalanced diet;
With various endocrinopathies, which are also very common and the cause of development is also;
After injury or surgery;
With prolonged stress;
With general chemical poisoning.

Clinical picture

The only symptom of anogenous alopecia is intense hair loss. Hair begins to fall out 1-3 weeks after the onset of negative effects on the follicles.

Hair falls out, both with external influences (when washing your hair, combing, styling), and for no apparent reason. As for external influence, it develops due to wearing tight hairstyles.

There are no painful or other subjective sensations with this type of alopecia. There are no signs of inflammation on the skin in the areas of alopecia foci, the skin retains its natural color, does not peel off, and there are no rashes on it.

In most cases, anogenic alopecia is a reversible condition. After eliminating the cause that caused hair loss, their growth is restored on its own.

Diagnostic methods

As a rule, in most cases, the causes of the development of anagen alopecia are known to the patient himself, so there are no problems in the diagnosis.

Otherwise, the patient should be referred for a comprehensive examination to identify the causes that led to hair loss. The patient needs a consultation with a dermatologist, trichologist, endocrinologist, neurologist, gastroenterologist.

It will be necessary to conduct a survey of the gastrointestinal tract, in order to exclude dysbacteriosis. Be sure to prescribe tests to determine the hormonal status, a study of blood and hair for the content of trace elements is carried out. In addition, examinations may be required to exclude helminthiasis and fungal infections (for example,).

Treatment

As already mentioned, anagen alopecia is a reversible condition. After the elimination of negative factors, hair growth is restored on its own. If the cause of alopecia was treatment with chemotherapy or radiation, then you just need to wait until the end of the course of treatment. After its completion, the hair will begin to grow without additional therapeutic measures.

After eliminating the causes that led to anagen alopecia, the following can be prescribed to accelerate hair growth:

Carrying out vitamin therapy and taking drugs that have a general strengthening effect. Perhaps, a reception of specially designed complexes to improve hair growth will be prescribed. These funds include Pantovigar or Merz.
Carrying out darsonvalization - a method of influencing the scalp with high-frequency current pulses. The procedure is carried out using an electrode that looks like a comb with sparse teeth, moreover, the role of the teeth is performed by electrodes that produce impulses.
To improve the nutrition of the follicles, it is necessary to stimulate the flow of blood to the head. To do this, use external preparations that have a slight irritant effect, for example, an alcohol solution of Minoxidil.

Treatment with folk methods

Alternative methods of treatment can be used to stimulate hair growth after eliminating the causes that caused anagen alopecia.

An effective remedy for accelerating hair growth is tincture of hot pepper alcohol. This remedy has an irritating effect and stimulates blood flow to the hair follicles. Pepper tincture can be bought at pharmacies or prepared independently. To do this, for 250 ml of vodka, you should take two medium-sized pods of hot red pepper. Infuse the composition for 21 days, then strain and gently rub into the scalp. When applying the tincture, a burning sensation will be felt. By the way, pepper tincture is also very effective in treatment.

Medicinal plants such as burdock root, willow bark, and nettle herb help well in the treatment of manifestations of alopecia. Decoctions should be prepared from these plants and used after washing to rinse the head.

The use of walnut oil stimulates the nutrition of hair follicles. It is necessary to grind 20 hazelnuts (together with the peel) and pour 100 ml of burdock or olive oil. After three weeks of infusion, the oil is filtered and used for rubbing into the scalp.

Forecast and prevention

Prevention of anagen alopecia is to avoid stress and timely treatment of diseases. If the manifestations of alopecia were the result of radiation or chemotherapy used to treat cancer, then you need to understand that this is a temporary phenomenon and in no case should you interrupt the course of the prescribed treatment.

The prognosis for anagen alopecia is good. After the provoking causes are eliminated, hair growth is restored.

It is very important to have at least a basic knowledge about the structure of hair and the mechanism of their growth. This knowledge will greatly contribute to understanding the processes occurring during treatment, which will ultimately save your nerves.

For a general understanding, it is enough to get acquainted with the first two sections. In the third part, the processes are described at a deeper level.

Hair Growth Cycles

Hair grows in cycles. There are 3 stages of the hair growth cycle:

Anagen- active stage of growth. The average duration of this stage varies from source to source, but a value of 2-7 years is more commonly used. At any given time, 85-90% of the hair on your head is in this stage.

Catagen- transitional phase. At this point in the cycle, the hair shaft factory stops and follicle cell apoptosis occurs. The duration of catagen is 2-3 weeks. Percentage of hair at this stage: 1-3%.

Telogen- resting stage of the follicle. The old hair is still in the skin, but its growth has already been completed. The duration of telogen is approximately 3 months, the percentage of hair at this stage: 10-15%.

Exogen- stage of hair loss. After the end of catagen, at some point, the stage of a new anagen is initiated, a new hair begins to be produced, which “pushes out” the old one.

Growth cycles are NOT synchronized. This means that at one point in time, the hair is at different stages of its cycle.

Now consider the structure of the hair follicle.

The structure of the hair follicle

(click to enlarge)

Dermal papilla

(in Russian-language literature also "hair papilla")

The papilla is a fairly large structure at the base of the hair follicle. The papilla consists mainly of connective tissue and a capillary network. Cell division in the papilla is either rare or completely absent.

Matrix

Surrounding the papilla is the hair matrix, a collection of epithelial cells often interspersed with pigment-producing cells, melanocytes. Cell division in the marix produces cells that form the basic structures of the hair and inner root sheath. The matrix completely envelops the dermal papilla (which is usually ovoid or pear-shaped) apart from a short stalk-like connection to the surrounding connective tissue.

root sheath

The root sheath consists of an outer and an inner layer. The inner root sheath consists of three layers: the layer of Henle, the layer of Huxley, and the inner cuticle, which is the outer layer of the hair.

Bulge

(the Russian-language analogue of this name does not yet exist)

The bulge area is located in the upper third of the follicle in the anagen phase under the sebaceous duct in the area of the insertion of the ARRECTOR PILI (lifting hair muscle). Here are several types of stem cells that supply new cells to the follicle, and are also able to participate in the restoration of the epidermis in case of damage.

Other structures

Other structures associated with the hair follicle include the sweat and sebaceous glands that cover the skin with a protective film. Attached to the follicle is a tiny bundle of muscle fibers called Arrector Pili. With the contraction of this muscle, the hair, usually inclined or adjacent smoothly, becomes perpendicular to the surface, ruffles. As a result of this process, goosebumps are formed.

How hair growth stages are initiated

Immersion

Signaling system of cellular interaction of the follicle

During the hair growth cycle, the epithelium and mesenchyme exchange a specific set of molecular signals that are unique to telogen, anagen, or catagen. The transition of the hair follicle from late telogen to active growth in anagen is initiated by a signal from the dermal papilla, causing vertical migration of stem cells from the bulge area down to the germinal zone. Here, under the action of dermal signals, active proliferation is initiated ( approx.: proliferation of body tissue by cell division) and the implementation of the differentiation program (in the process of differentiation, a less specialized cell becomes more specialized) of epidermal cells. This is possible due to the anatomically close location of the bulge and the dermal papilla in the degenerated follicle. However, it should be noted that there are other hypotheses regarding the mechanism of activation of epidermal stem cells.

Meanwhile, the interfollicular epidermis retains the ability to respond to morphogenetic signals from the cells of the hair papilla, which in some cases ensures the formation of new hair follicles. For this, the preservation of the dermal papilla cells and their specific induction properties is absolutely necessary. The cells that form the connective tissue membrane of the hair follicle also have an inductive signal, since these cells are able to form a new dermal papilla when it is removed.

The transition from the telogen to anagen phase is associated with the activation of Shh, Wnt/betacatenin/Lef-1, and Stat3 signaling pathways. At the same time, the inhibitory BMP pathway is suppressed.

In the anagen phase in the epithelium and mesenchyme, a huge number of signal transduction pathways and factors (BMP, FGF, HGF, IGF, PDGF, SCF, Shh, Wnt) are activated, the coordinated activity of which is necessary for hair formation. Proliferating and postmitotic matrix keratinocytes express receptors ( approx.: a molecule (usually a protein or glycoprotein) on the surface of a cell, cell organelles, or dissolved in the cytoplasm; transmits an external signal to enter the cells) or components of various signaling pathways (beta-cateinin/Lef-1, c-kit, c-met, FGFR2, IGF-IR), while dermal papilla cells secrete the corresponding ligands ( approx.: «.. a substance that binds specifically to a receptor is called a ligand for that receptor.") (Wnt5a, SCF, HGF, FGF7, IGF-1). Conversely, dermal papilla cells express PDGF-Ralpha receptors, receptors for Smoothened and TrkB, and the corresponding ligands (PDGF-A, Shh, and BDNF) are secreted by matrix keratinocytes. Thus, epithelial-mesenchymal interactions in the hair follicle are of a reciprocal nature. Completion of anagen-specific signaling between the epithelium and mesenchyme leads to apoptosis of epithelial cells, and activation of other signaling pathways causes the transition of the dermal papilla to the resting phase. It should be noted that the same factors can have a completely opposite effect on the cells in the follicle in different phases of the cycle.

In the catagen phase The "factory" for the production of the hair shaft (that is, the matrix of the hair follicle, and indeed the entire hair follicle) almost completely disappears as a result of controlled processes of apoptosis and terminal differentiation. Strict control of involution ( note: reduction or loss in the process of evolution of individual organs, simplification of their organization and functions) of the hair follicle is necessary to avoid complete degradation of the organ.

Telogen traditionally considered the phase of the least proliferative and biochemical activity of the hair follicle, that is, the resting phase. However, there is evidence that indicates the extreme importance of this phase of the cycle, since a number of genes are most active during this period (for example, estrogen receptors).

The nature of intercellular interactions and control of the hair follicle cycle is not the same for different types of hair and depends on the location on the body. However, the fundamental patterns undoubtedly coincide. There is a huge potential here for the development of methods for correcting and managing the cycle with the help of biologically active substances, growth factors and hormones. The action of growth factors and modulators can be directed to:

Interruption of telogen (activation of stem cells);

Stimulation of hair growth (stimulation of the proliferation of matrix cells);

Deceleration of degeneration (inhibition of apoptosis);

Improved blood supply;

Preservation of the specific activity of dermal papilla cells (when using cellular technologies).

Bibliography:

http://en.wikipedia.org/wiki/Hair_follicle

https://ru.wikipedia.org/wiki/%D0%92%D0%BE%D0%BB%D0%BE%D1%81%D1%8F%D0%BD%D0%BE%D0%B9_%D1 %84%D0%BE%D0%BB%D0%BB%D0%B8%D0%BA%D1%83%D0%BB

http://www.pscj.ru/upload/iblock/aee/13.pdf

Hair grows on the entire skin of a person, with the exception of the palms and feet. On our body there are areas with dense vegetation, as well as barely noticeable, almost transparent hairs. Initially, their role was to protect. But in the process of evolution, the functions have changed and become an attribute of decorativeness, rather than necessity.

In order to effectively perform various hairdressing procedures, such as dyeing, bleaching, perming or straightening, you need to know what the hair consists of, what elements are involved in the reaction when applying dye, caring or changing the shape of substances. Let's learn about the structure of a human hair, how and from what its flask, follicle, shape and color are formed.

Changes in the structure of hair throughout a person's life

During observations by scientists of the process of human hair growth, it was found that their formation occurs even before birth, and at different stages of life, their structure changes. How does this happen?

First appear cannon. They grow at birth and remain with the child until the age of three. The name itself says that their structure is very soft and thin.
At the age of three to sixteen, a child begins to form teenage hair, which develops into a genetically incorporated type and it is already possible to determine what it will be like in the future.
In adolescence - 16-17 years old, the hair passes into the stage of maturity. And by the age of 18, the formation of their structure is finally completed.

During puberty, men appear vegetation on the body and face - mustaches, beards. And for women - only on the body. By old age, the elderly have an intensive growth of eyebrows, hair appears in the ears and their number in the nose increases. With age, the structure becomes stiffer, and the bulb deepens into the skin.

Growth begins due to active cell division in the outer layer of the skin. This overgrowth is called the "hair germ", which then takes on a teardrop shape and subsequently becomes a follicle. As the drop (tongue) deepens into the skin, the cell continues to divide. This overgrown accumulation of cells turns into a hair papilla, which is overgrown with protein and a head with a pointed tip is obtained - a bulb. Thus, the protein in the hair is formed even before it appears on the surface of the skin. In the structure of the follicle, and then the bulb, cells are involved - melanocytes, in which the future pigment is laid, as well as a protein - keratin, consisting of amino acids.

The nutrition of the root and the influx of building materials is carried out through the papilla connected to the blood vessel, from which hair growth begins. The follicle becomes horny and a small process appears through the hole formed in its core, which, breaking through the skin layer, gets out.

The new (primary) hair is called papillary because it feeds directly from the blood vessel. Gradually, the supply of keratin from the papilla stops, the hair grows into the canal more strongly, its growth stops and loses contact with the nourishing organ, and the bulb becomes horny completely. In this condition, the hair is called cone-shaped. They remain in the skin for a long time, so most of the human vegetation consists of them.

Then, the cell mass located under the flask-shaped hair begins to divide again and forms a new tissue that pushes out the old one. A young hair that has grown in place of a fallen hair is called secondary. This is a continuous natural process. The daily rate of loss is 60-100 hairs. Their maximum life span is 6 years.

Hair growth phases

Since replacing old hair with new ones is a permanent process, it has a certain cycle, which consists of several phases:

anagen;
catagen;
telogen;
early anagen.

What do they mean?

Anagen is the phase of active cell division in the hair follicle. During the growth of the bulb in the skin around it, the synthesis of ribonucleic acid begins. In this phase, the hair papilla receives the most intensive nourishment from the blood vessels. At the same time, the bulb is connected to the nerve endings - therefore, pain occurs when the hair is pulled out from the root. In the anagen phase, pigment is also laid down. This stage of growth completely forms the bulb and future hair, the life span of which will last from two to six years.
Catagen is an intermediate phase that occurs after active growth. During this period, the supply of nutrients to the papilla and the synthesis of melanocytes are stopped. Hair growth stops and keratinization of the follicle occurs. The intermediate stage lasts 2-3 weeks.
Telogen is the resting phase when the bulb becomes completely inactive. Nutrition ends and the papilla goes into a state of rest, but the hair flask remains on the surface for another 2-3 months, and then painlessly leaves its sac. About a hundred telogen hairs fall out every day. The total duration of this phase can be up to six months.
Early anagen is a period of active formation of secondary hair under the old flask that has not yet fallen out.

This process is continuous, but with age it slows down, and the anagen phase is shortened. Over time, some of the follicles lose their ability to form new hair. And in some cases, most of them completely die off and alopecia sets in - partial, and then complete baldness.

hair shape

The way the hair will be - straight, wavy or very curly depends on the shape of the channel in which the bulb is born.

Straight hair is formed from a straight channel.
Wavy - from crescent. The more the channel is bent, the more curly.
Tight black curls grow out of spiral channels.

Thus, the future shape of the hair is laid even before it appears on the surface of the skin.

If you look under a microscope at different types of hair in cross section, you can notice the following differences.

Asian ones are most often thick, straight and hard, and their cross section is round.
European ones are usually of medium thickness, slightly wavy, the section is elliptical.
Negroid - hard, curly, in the context they have a ribbon-like shape.

The shape of the channel affects not only how the hair will be, but also its cross section.

hair structure

When examining a section of a human hair through a microscope, you can see that it consists of three main layers:

scales - cuticles;
bark - cortex;
and the core - the rod, medulla or medulla.

It also has a cylindrical shape.

Let us consider in more detail the structure of all layers.

The hair cuticle (scales) is a protective layer from external influences. It consists of horny leaves arranged in a checkerboard pattern, which look like a spruce cone or fish scales. These petals are sensitive to alkaline or acid attack.
The cortex has a complex structure. It is formed from elongated fibers intertwined with each other. This layer contains pigment, hydrogen and sulfur bonds, and nutrients.
The structure of the rod (medula) is formed from the brain cells that make up the base of the flask. The remaining layers are attached to this core.

In addition, adipose gland and muscle are also involved in the formation of hair.

The fatty gland is responsible for elasticity, preventing keratinization of the hair and scalp. As well as the production of sebaceous secretion - a natural fatty film, protects against the penetration of surface contaminants.
The muscle presses the hair against the scalp, creating protection from the cold, or during a nervous shock. The figurative expression - "hair stood on end", becomes real thanks to this particular muscle.

Each component in the structure of the hair is responsible for a separate function.

The structure of the human hair

Chemical composition

The whole person consists of the elements of Mendeleev's periodic table. The chemical composition of the hair needs to be known in order to predict the reaction of various drugs when performing long-term styling and dyeing procedures.

The ratio of chemical elements in the hair is as follows:

carbon (C) - 49.6%;
oxygen (O) - 23.2%;
nitrogen (N) - 16.8%;
hydrogen (H) - 6.4%;
sulfur (S) - 4%.

They affect the quality of staining, the durability of the pigment, as well as the formation or straightening of the curl.

The substances that make up the hair form a fibrillar protein - keratin and all its amino acids. This is the main building material.

Keratin is made up of the following amino acids:

alanine;
arginine;
aspartic acid;
valine;
glycine;
histidine;
glutamic acid;
isoleucine;
leucine;
lysine;
methionine;
proline;
serine;
tyrosine;
threonine;
tryptophan;
phenylalanine;
cystine.

The lack of at least one amino acid in a human hair leads to their fragility, and the bulbs to irreversible death and loss. Keratin has high mechanical strength, second only to chitin, which forms the keratinized parts of animals.

Types of connections

When the color changes as a result of dyeing, or the shape of the hair when curling or straightening, its hydrogen or sulfur bond changes. What is it and what effect do chemicals have on it?

Hydrogen (longitudinal) bonds are single bridges located along the hair. They are responsible for changing the natural or cosmetic pigment. The reaction of dyes is based on the action of hydrogen oxide with the fibrous substance of the cortex.
Sulfur (cross) bonds are double bridges located across the hair. They are less brittle than hydrogen. They are responsible for the shape - the stronger the disulfide (double sulfuric) bond, the more intense the curl. The main reaction of preparations for long-term styling lies in the action of sulfur-containing compounds with these bridges in the cortex.

All modern chemical agents are synthesized from components that are most similar in composition to a human hair, so that they are embedded in its fibers and do not break bonds, but delicately stretch them.

Pigment

This is the color that the human eye sees. It is laid before birth and depends on genetic characteristics. Color is formed in the cortex from melanocyte cells, which are two types of natural pigments:

melanin - black or brown;
pheomelanin - red or yellow.

The natural base is formed by combining these types of pigments. This is the color that is given to a person at birth.

But pigments can also be cosmetic - this is an acquired color with the help of staining. When creating a cosmetic base, the dye molecules push out the natural pigment and are embedded in the resulting voids.

Let us summarize by recalling the main theses. Hair covers almost the entire body, with the exception of the feet and palms. Their structure and structure depend on the period of a person's life. In newborn children, they are fluffy, and after three years they turn into teenage ones. The final formation is completed by puberty. The origin of the hair occurs even before the birth of the child. Its color and shape depend on the genetic disposition of a person. Before the hair tip appears on the surface, complex biochemical processes of cell division take place inside the skin, the formation of a papilla from them, connected to a blood vessel, and then overgrown with nerve endings. Hair growth and loss is a natural and continuous process. The cycle consists of three main phases - anagen, catagen, telogen, as well as one additional - early anagen. The daily rate of loss in an adult is 60-100 pieces. Thus, the growth of new hair does not stop until the end of life.

Hair structure - cuticle

Hair structure - cortex and medulla