The structure of human hair

Impressive hair facts:

Hair diameter: 0.1 mm, growth per day: 0.3 mm, hair growth per month: 1 cm, hair density: 200 follicles per cm², lifecycle: 2-5 years, load carrying capacity: 100 g per hair.

The structure of the hair

Visible hair is only a part of the hair system. The hair root, also called the hair follicle, reaches deep into the skin.

The hair structure consists of the hair root and the hair follicle. The hair papilla lies under the dermis and builds the hair and is therefore more or less the foundation of the hair. The hair shaft is formed when the keratin stem cells within the follicle grow above the skin surface. The hair follicle is a longitudinal indentation in the epidermis in which the hair shaft runs. A sebaceous gland flows into the follicle.

People with brown or black hair have around 100,000 hair follicles on their head; blond people have more (approx. 150,000) and red heads have less (approx. 75,000). The hair colour is mainly determined by the melanin. This is produced in the cells of the hair bulb (melanocytes) and released into the hair roots.

The different hair colours are inherited and are a result of the different type, quantity and distribution of melanin. Grey hair occurs when these melanin molecules are no longer produced.

The hair cycle

New hair grows every day and every day hair falls out. This cycle is repeated without interruption and is completely natural! The hair cycle consists of three phases: 1) The growth phase 2) the transition or stoppage phase 3) the resting phase. Each hair goes through its own cycle independently of the other hairs. Growth phases that last several years alternate with shorter transition and resting phases. Finally, the club hair (as hair in the resting phase is called) is expelled within a few months. The length and density of hair is determined by the duration of the growth phase.

The growth phase

During the growth phase, the hair grows through the division of cells. Around 80% of the hair on the head is in this phase at a given time. It is the longest phase in the hair cycle and lasts between 2 to 5 years. The longer the growth phase lasts, the longer the hair will naturally also grow during this time. On average, you can say that human hair grows around 1 cm per month.

The transition phase

The transition or resting phase only lasts around 14 days and is the shortest of all phases in the hair cycle. Only a small proportion of hair follicles are in this phase at a given time. During the transition phase, the hair follicle contracts and is pushed up to the skin surface. The hair is then known as the club hair because of the shape it takes. It has reached the maximum length and no longer grows.

The resting phase

The resting phase immediately follows the transition phase. This is the last phase in which the club hair is pushed out by the growing new hair. Then a new cycle begins. The duration of a hair cycle varies according to age. It also determines the length and density of the hair.
It is also quite natural to shed hair. In the normal hair cycle, the hair grows, rests and falls out to allow new hair to grow. Under normal conditions, an average of 80-100 hairs are shed. If the number of hairs lost is clearly higher, the cycle may be disrupted. This is pathogenic hair loss.


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