Hair , general data …

H air has a diameter of  50 to 100 micrometers (a millimiter, i.e. 1,000 micrometers, is then equivalent to  10 to  20 hair's diameter ) . Their growth is slow : the guess is that hair grows about  1 cm per month , and one loses from 50 to  100 hair every day .
Depending on the ethnic origin , hair texture may be different : crisp , thin , straight or curly . This depends on the implantation of hair follicles . For example , straight follicles give a very stiff hair as for people from Asia, while more supple follicles provide a wavy or curly hair . Further, there is a wide range of colours from a very light blonde to dark brown . As for skin or eyes , hair colour is due to the well-known melanin which gives the hair fiber its colour.

Structure of the hair follicle and hair

The hair follicle ( the hair entire structure ) works after a cycle, which makes new hair on a regular basis.
This follicle comprises different parts:
• The hair implanted into the hair follicle.
• The sebaceous gland opened to the hair canal . Each hair follicle is connected to a sebaceous gland ; hair and sebum follow the same way to reach the outer skin .
• The piloerectile muscle , a muscle at the bottom of every hair . It is active in the thermoregulation process, through reflex goosebumps .

Hair comprises a visible part called the hair shaft and a deep end : the root .

Hair growth

Hair bulb is the birth place. Due to cells divisions , hair springs , then grows up and up to the surface of skin . Hair growth goes in three stages :
• The anagen stage : cells multiply, allowing for the growing of hair. This phase is also when the synthesis of melanin is at its highest rate, giving hair its colour.
• The catagen stage is a resting phase ; cells division s and synthesis of melanin end .
• The telogen stage is the phase of getting rid of the "dead hair", which eventually fall s down by itself.

Thus, along our life , hair follows a cycle of continuous growth : when hair dies , a new one is given life in the hair bulb.

Hair and Cosmetics

H air, as we call it, or better, hair shaft ( the visible part ) is biologically dead . However , it acts as a " blot " absorbing materials applied on it. Cosmetic products used on hair sheathe hair and improve its aspect, without any true action as the fiber is biologically inert.