Hair is keratin filaments whose lower part (hair root) is embedded in the skin. Read more about the structure and function of the hair!


The hair are structures made of keratin, which in humans and mammals cover the whole body more or less densely. They protect against the effects of the weather and increase the sense of touch. They also have the function of a group membership in humans and are an expression of life attitudes and values. Read all about the topic: What is Hair? How are they developing? What health problems can affect the hair?

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  • What are the hairs?

  • What is the function of the hair?

  • Where are the hairs?

  • What problems can the hair cause?

What are the hairs?

Hair is long horn filaments made of keratin. As so-called skin appendages they form from the third embryonic month in the epidermis.

There are three types of hair in humans:

  • Lanugo hairs (fluffy hair): fine, short, thin and unpigmented hair that occurs during the embryonic period and repelled at the latest by the 4th month of life.
  • Vellus hairs: These short, fine, slightly pigmented hair first replace the Lanugo hairs. They form in children, but partly also in women's body hair.
  • Terminal hairs (permanent hair): usually long, thick and more or less pigmented hair, which form the head hairs, eyelashes and eyebrows since birth. During puberty, hairy hair in the armpits and genital area becomes such terminal hair. The same goes for the majority of male body hair.

Hair: build up

Hairs arise from cone-shaped attachments in the depth of the epidermis, which grow into the embryonic connective tissue. This results in the hair papilla, a blood-borne connective tissue spine. Around it sits the hair bulb, the thickened end of the hair root, which extends obliquely into the subcutaneous tissue.

Externally visible is only the protruding from the skin hair shaft. The hair is outwardly surrounded by a simple, keratinized squamous epithelium (cuticle), which has upturned, jagged edges. These edges overlap one another like a tile. When they are close together, the hair looks smooth and shiny. But when they stand apart, it looks brittle and lackluster.

Since the hair is diagonally in the skin, one direction, a "dash" can be seen. This is particularly visible in vertebrae that form the hair.

Between the hair follicle and the surface of the skin there is a hair follicle muscle, which can contract when aroused, causing the hair to rise and make the skin surface look like goose bumps.

Whether hair is smooth or curly is due to the cross section of the hair shaft. If the cross section is round, they are usually very smooth. In a round to oval cross-section they are smooth or can form curls. In a strongly elliptical cross section, they usually form very strong, small curls.

The development of a hair occurs cyclically, and each hair follicle or hair follicle has its own cycle, which is independent of other hair follicles. The cycle can be divided into three sections: anagen, catagen and telogen.

Hair development: anagen phase

The hair bulb takes on different shapes during the development of the hair shaft:

In the growth phase (Anagen phase), in which a new hair is formed, a new bulb is formed in the hair root, which is layered by continuous neoplasm of cells in several layers. There is a high metabolic activity, but also a high sensitivity to pollutants of all kinds.

The Anagen phase lasts two to six years and depends on the age, sex and the place where the hair grows. About 90 percent of the hair is in the anagen phase.

Hair development: catagen phase

In the transition phase (catagen phase), the metabolic activity and thus cell production of the hair bulb ends - it is closed and keratinized (storage of keratin). The hair is rounded down and enclosed by the outer sheath of the hair root and slowly moves upwards.

The catagen phase lasts one to two weeks. It contains about one percent of the hair on the head.

Hair development: telogen phase

In the final or resting phase (telogen phase), the onion is displaced, the inner hair root sheath disappears and the newly formed matrix renews the hair papilla and cell division begins again. It forms a new "anagen hair" which then ejects the hair of the hair in its telogen phase.

In this phase, about 18 percent of the hair is on the head. The Telogen phase lasts two to four months.

How many hair does a human have?

The number of hairs is about 90,000 to 100,000. However, there are marked differences between people with different hair colors: On average, most hair has blond people with around 140,000. Then follow brunette people with about 100,000 hair on the head. Redheads with only about 85,000 hair make up the rear.

Despite differences in the total number but the number of hair that fail daily, the same for all: The natural loss of hair is about 70 to 100 hairs per day.

The hair grows daily by about 0.3 millimeters, about one centimeter a month. The hair thickness (diameter / hair) is 0.04 millimeters for the vellus hairs and 0.12 millimeters for the terminal hairs. The density is about 200 hairs per square centimeter.

The haircolour

The color of the hair is created by pigments, which is formed by certain cells, the melanocytes. These cells are abundant in the hair bulb area. When air enters the hair park, it causes graying. The initial mix of colorless and natural-colored hair gives the impression of "gray". If all hair is pigment-free, they look white.

What is the function of the hair?

In many animals, the hair is important for thermal insulation, as protection against external influences and as orientation and tactile organs. In humans, these hair functions no longer play a major role. Only special hair has a protective function. The head hair protects against the effects of cold and UV rays and the hair in the nose and ear canal from the penetration of dust particles.

In addition, human hair (such as animal) touch, pressure and tactile stimuli can pass - thanks to the many nerve endings on the hair root.

Last but not least, hair in all cultures has a significant function as jewelry.

Where are the hairs?

They are on the entire surface of the body with a few exceptions - palms and soles, finger inside, nipples and lips are hairless. Also mucous membranes are basically hairless.

What problems can the hair cause?

Purulent inflammation of the hairy gland is called boils. Its heaviest form is called Carbuncle. Several adjacent hair follicles are inflamed (with Gewebeinschmelzung).


Toxins damage hair especially in the anagen phase. The strength and duration of exposure to a pollutant and the sensitivity of the individual follicle play a role in the intensity of the injury.

For lighter pollutants, anagen hairs change prematurely into telogen hair, resulting in hair loss after two to four months (corresponding to the duration of the telogen phase).

For heavier pollutants, only part of the anagen hair is transformed into telogen hair. The majority of the sensitive anagen hairs become dystrophic and break off at the narrowest point, resulting in a rapid onset of hair loss.

For very high levels of pollutants, the conversion and onset of hair loss occur within hours to days.

Extremely strong or suddenly acting pollutants within hours lead to a sinking of the entire hair matrix: the hair breaks and falls out.

Hair loss and hair loss

The formation of a bald head in men is based on a hereditary predisposition. She can use shortly after puberty.

Androgens (male sex hormones) like testosterone have different effects on hair growth. The development of the scalp hair is inhibited, it comes to hair loss and baldness (where also inheritance and age play a role). The development of body hair in men, however, is promoted by androgens.

In some people, it suddenly comes to a circular hair loss (alopecia areata). For example, it can affect the hair on the head, beard, under the armpits, in the genital region or the eyebrows.

A hair deficiency (hypotrichosis) can have a variety of causes, such as metabolic disorders (such as iron deficiency or malnutrition), hormonal changes (such as during pregnancy, lactation and menopause) or infectious diseases (such as typhoid fever, late syphilis, influenza). Hypotrichosis can also be hereditary and congenital.

Excessive hair

In women, an excess of androgens leads to a male hair type (hirsutism). The cause remains unclear in some cases. In others, the reason is an overproduction of testosterone (such as in ovarian tumors, Cushing's disease, obesity or polycystic ovarian syndrome).

People with the so-called hypertrichosis congenita carry on the body long, dense, silky hair: The innate Lanugo hair persists and is not replaced by Vellus hair. Those affected are often colloquially called "monkey humans".

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