What is hair?
Hairs are long horny threads consisting of keratin. As so-called skin appendages, they form in the epidermis from the third embryonic month.
There are three types of hair in humans:
- Lanugo hairs (downy hairs): fine, short, thin and unpigmented hairs that occur during the embryonic period and are shed by the 4th month of life at the latest.
- Vellus hairs (woolly hairs): these short, fine, slightly pigmented hairs initially replace the lanugo hairs. They form the body hair in children, but partly also in women.
- Terminal hairs (permanent hairs): usually long, thick and more or less pigmented hairs that form the head hair, eyelashes and eyebrows since birth. During puberty, vellus hairs in armpits and genital area become such terminal hairs. The same is true for most of the male body hair.
Hair: Structure
Hairs develop from cone-shaped plants in the depth of the epidermis, which grow into the embryonic connective tissue. This develops into the hair papilla, a cone of connective tissue that is supplied with blood. Around this sits the hair bulb, the thickened end of the hair root, which extends obliquely into the hypodermis.
Since the hairs stand at an angle in the skin, a direction, a “line”, can be seen. This is particularly visible in swirls that form the hairs.
Between the hair bellows and the skin surface runs a hair bellows muscle, which can contract when excited, causing the hair to stand up and make the skin surface look like a “goose bump”.
Whether hair is straight or curly depends on the cross-section of the hair shaft. If the cross-section is round, they are usually very smooth. If the cross-section is round to oval, they are smooth or may form curls. If the cross section is strongly elliptical, 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 phases.
Hair development: Anagen phase
The hair bulb takes different forms during the development of the hair shaft:
During the growth phase (anagen phase), when a new hair is formed, a new bulb is also formed in the hair root, which is layered in several layers due to continuous new cell formation. There is a high metabolic activity, but also a high sensitivity to pollutants of all kinds.
Hair development: catagen phase
In the transition phase (catagen phase), the metabolic activity and thus the cell production of the hair bulb ends – it is closed and keratinized (storage of keratin). The hair is rounded at the bottom and enclosed by the outer sheath of the hair root and slowly moves upwards.
The catagen phase lasts one to two weeks. About one percent of the hair on the head is in this phase.
Hair development: telogen phase
In the final or resting phase (telogen phase), the bulb is displaced, the inner hair root sheath disappears and the newly formed matrix renews the hair papilla and cell division begins again. A new “anagen hair” is formed, which then expels the bulb hair in its telogen phase.
About 18 percent of the hair on the head is in this phase. The telogen phase lasts two to four months.
How many hairs does a person have?
The number of hairs on the head is about 90,000 to 100,000, but there are significant differences in people with different hair colors: On average, blond people have the most hair with around 140,000, followed by brunettes with around 100,000 hairs on their heads. Redheads bring up the rear with only about 85,000 hairs.
The hairs grow by about 0.3 millimeter per day, i.e. about one centimeter per month. The hair thickness (diameter/hair) is 0.04 millimeters for vellus hairs and 0.12 millimeters for terminal hairs. The density is about 200 hairs per square centimeter.
The hair color
The color of the hair comes from pigments produced by certain cells called melanocytes. These cells are found abundantly in the area of the hair bulb. When air enters the hair marrow, it causes graying. The initial mixture of colorless and natural colored hair gives the impression of “gray”. When all hairs are pigment-free, they look white.
What is the function of hair?
In many animals, hair is important for thermal insulation, as protection against external influences, and as organs of orientation and touch. In humans, these hair functions no longer play a major role. Only special hairs still have a protective function. For example, the hairs on the head protect against cold and UV radiation, and the hairs in the nose and ear canal protect against the penetration of dust particles.
In addition, human hair (like animal hair) can also transmit touch, pressure and tactile stimuli – thanks to the many nerve endings at the root of the hair.
Last but not least, hair has an important function as jewelry in all cultures.
Where is the hair located?
What problems can cause the hair?
A purulent inflammation of the hair follicle gland is called a furuncle. Its most severe form is called a carbuncle. In this case, several neighboring hair follicles are inflamed (with tissue fusion).
Harmful substances
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 damage.
In the case of lighter pollutants, anagen hairs prematurely transform into telogen hairs, which leads to hair loss after two to four months (corresponding to the duration of the telogen phase).
In the case of stronger pollutants, only a part of the anagen hairs is converted into telogen hairs. The majority of the sensitive anagen hairs become dystrophic and break off at the narrowest point, leading to rapid onset of hair loss.
With very strong pollutants, the transformation and onset of hair loss happen within hours to days.
Extremely strong or sudden pollutants cause the entire hair matrix to perish within hours: Hair breaks and falls out.
Hair loss and hair deficiency
The formation of baldness in men is based on a hereditary predisposition. It can begin shortly after puberty.
