Hair growth is inseparable from hair follicles, and the existence of hair follicles is the premise to ensure hair growth and replacement. During the growing period, the hair follicle is active, the cells at the bottom of the hair bulb divide vigorously, and the separated cells move upward continuously. When the keratin of the soft capsule in the hair follicle is transformed into hard protein, the hair is pushed out of the skin and visible to the naked eye. When the hair grows near the end of the growth period, the cells of the hair bulb stop proliferating, the hair follicle begins to shrink and the hair stops growing. This is a retrogression period. At rest, all parts of the hair will age, degenerate and shrink, and the hair will fall off. At the same time, a growing hair ball is formed near the aging hair follicle, and a new hair is born.
The following are the different growth stages of hair: (1) growth stage; Also known as growth activity period, the growth period can last for 4-6 years or even longer, the hair is in an active proliferation state, the cells in the lower part of the hair bulb divide rapidly, and the cells in the upper part of the hair bulb differentiate into cortex and small fur; Dermal papilla is enlarged, cell division is accelerated, and the number is increased. The original inactive melanin grew dendrites and began to form melanin. (2)CATAGEN； Also known as atrophy or degeneration, it lasts for 2-3 weeks. The positive proliferation of hair stops, forming rod-shaped hair, with eosinophilic homogenate at the lower end and bamboo sticks at the periphery. The inner hair root sheath disappeared, the outer hair root sheath gradually keratinized, the hair bulb was flat without depression, the hair papilla gradually narrowed and the number of cells decreased. Black cells lose their dendritic processes and are round and inactive. (3) rest period; Also known as hibernation or hibernation, it lasts about 3 months. At this stage, the hair follicle gradually shrinks, forming 1 growing hair ball near the aging hair follicle, and finally falling off, but at the same time, new hair will enter the growth period and repeat the cycle. In the scalp, 9%- 14% of the hair is at rest, only 1% is at regression, and 90% of the eyebrows are at rest. The proportion of hair in different stages of the growth cycle varies with different parts.
3. Factors affecting hair growth; The density of hair varies with gender, age, individual and location. Adult males are estimated to have 5 million hair follicles, of which 6.5438+0 million are in the head and about 6.5438+0 million are in the scalp. Hair follicle density on forehead and cheeks is 4-6 times that of trunk and limbs. It is generally believed that the density of hair follicles is born first, and the number of new hair follicles cannot be increased after adulthood. The growth rate of hair is related to its position, and the head grows fastest, with a daily growth rate of 0.27-0.4MM, with an average of 1.9CM per month, and other parts grow about 0.2MM per day. Men's hair generally grows faster than women's. 15-30 years old grows fastest, and hair growth slows down in old age. It grows faster in summer. The periodic changes of hair growth and rest are regulated by endocrine, and some people think it is related to ovarian hormones. In addition, nutrients have an effect on hair growth; It also has an impact. Vitamin B complex can affect hair growth and cuticular keratinization. When treating tinea capitis with vitamin A, it will lead to hair loss, and the reason is excessive vitamin A. ..
I. Glands
① gonad: Androgen plays an important role in stimulating the growth of hair mother cells.
② Adrenal gland: If the androgen secretion of adrenal cortex is strong, it can cause hirsutism in women. But it is also related to the function of pituitary gland. If the pituitary gland function deteriorates, the hair may be reduced or shed.
③ Thyroid gland: Normal thyroid function plays an important role in hair growth. If it is dysfunctional, the hair on the outside of the eyebrows (1/3) will fall off. When the function declines, not only the color will be grayish white, but also the hair will decrease or fall off. The growth and shedding of hair are mainly controlled by the growth period of hair itself, but also influenced by race, endocrine, disease, mental state, gender, age, season and other factors.
(1) Race: Racial differences are obvious phenomena. People of different races not only have different hair colors, but also have different hair quantity and growth conditions. Baldness is common among whites, less in China and even rarer among Indians.
(2) Heredity: In the same family, the growth of hair is often roughly the same. Male baldness is closely related to heredity.
(3) Endocrine: Androgen can directly act on hair follicles, leading to male baldness. People who lack androgen stimulation (such as eunuchs) will not have this phenomenon. Estrogen has the function of antagonizing androgen, so women seldom go bald before menopause. Hair thinning when thyroid hormone is insufficient, hair loss when adrenal gland function is low, and the function of anterior pituitary gland is reduced, which can lead to total baldness.
(4) Mental state: nervousness, fear and anxiety can obviously increase hair loss. It is reported that a condemned man loses more than 1000 hairs every day after being sentenced.
(5) Vitamins: Long-term lack of vitamin A will lead to thinning hair; Lack of vitamin B2 will increase sebum overflow, which will increase sebum overflow and make hair fall off easily. Vitamin B6 deficiency can lead to abnormal sebum secretion. Oral contraceptives can accelerate metabolism and consume more vitamin B6, which may be related to the diffuse hair loss of some women. In addition, vitamin B6 can affect the process of pigment metabolism, and when it is lacking, hair will turn gray and grow poorly; Deficiency of pantothenic acid (also called vitamin B3) will make hair turn white and grow poorly; Inositol belongs to vitamin B family, which can prevent hair from falling off. Lack of biotin (also known as vitamin H2) can make hair fall off; P-aminobenzoic acid also belongs to B vitamins, which can protect hair color and maintain normal hair growth.
(6) Trace elements: Some scholars observed the changes of trace elements such as zinc, iron, molybdenum, calcium, lead, magnesium, manganese and selenium in hair, and found that the values of zinc, copper, iron and manganese in patients with alopecia decreased significantly, while the values of calcium, magnesium and selenium increased significantly, and there was no difference in the values of elements in patients with atypical alopecia. Copper deficiency will affect the absorption and utilization of iron, poor iron metabolism will lead to anemia, mental excitement and other symptoms, the latter can be the cause of alopecia areata, copper deficiency will also affect the process of hair keratinization, thus affecting hair growth; Calcium plays a role by combining with calmodulin, and high calcium concentration may change the immune regulation function of the central nervous system, thus leading to hair loss; Excessive selenium will lead to hair loss due to autoimmune reaction and sebum overflow.
(7) Diseases: Some systemic diseases, such as febrile diseases, anemia, malnutrition, liver diseases and serious chronic wasting diseases, often lead to thinning hair.
(8) Gender and age: Women's hair grows faster than men's, and young people grow faster than the elderly, but this difference is not great. With the increase of age, the number of hair follicles in the head decreased significantly. According to statistics, according to the number of hair follicles per square centimeter, there are 6 15 in 20-30 years old, 485 in 30-50 years old and 435 in 80-90 years old.
(9) Other factors: Hair grows slightly faster in summer than in winter. This is because the increase of temperature can promote vigorous metabolism and lead to faster hair growth. Hair grows faster during the day than at night. X-ray can control sulfhydryl compounds in hair follicle matrix, thus causing temporary hair loss. Some chemical factors such as iron will affect the formation of keratinization, which may interfere with cystine's participation in keratin composition, thus affecting hair growth. Ultraviolet rays, drugs, trauma, chronic inflammation, dermatosis, local massage stimulation, etc. It also has a certain influence on the growth and shedding of the head.
So far, in the hairdressing questions I have received from readers, the growth rate of hair is often mentioned. Many readers write to tell us the secret recipe they have heard to make hair grow faster. For example, wash your hair with eggs and trim your hair at least once a month. And these are exactly what we call "hair witchcraft" in the industry. In other words, these "secret recipes" that can make hair grow faster have no scientific basis at all.
In short, apart from pregnancy and illness, no matter how much you care about hair growth, generally speaking, a person's hair can only grow half an inch at most a month. The growth rate in summer will be slightly faster than that in winter.