The human skin from head to toe covered with hair except the palms and soles. In humans, there is no question of a uniform distribution of hair growth as in most mammals. In humans, the visible hairs thicker and more pronounced on the head, the face (in men), in the armpits and the genital area. Human hair growth depends on age, heredity, race and hormonal factors. Hairs are produced in the hair follicles (hair follicles). The number of hair follicles on the scalp is around 100,000. This is different for every individual and genetically determined. For instance more people blond hair follicles on the scalp than people with black or reddish hair.
The hair growth cycle
The hair growth is a rhythmic process and continues through different stages:
-Growth phase (anagen phase)
Phase-Transition (kata grown phase)
Rust-phase (telogen phase)
In most mammals these phases run in sync with each other: when the hairs fall out in the telogen phase and that once this is done is known as "moulting" or "shedding." In humans, these phases run together: there is a balance between the number of hairs in growth phase and that in the resting phase gets. The hair density in humans is still (almost) constant.
The hair growth phase lasts an average of 3 years. When women take the growth phase of each hair longer than men. During the last year of growth will slow down cell division and the base of the hair thinner. Breaks the transitional phase where the growth stops completely and the hair is less firmly anchored in the hair follicle. In the resting phase that follows it will fail. After a few months come back to the hair follicle development and a new hair is produced.
Hair for Life
During human development in the womb, all hair follicles from which hairs grow later, all laid out. In this period before birth are producing all kind of hair follicles initially: lanugohaar. These woolly hairs are shed before birth already. Lanugoharen These are then replaced by vellus hair, non-pigmented hairs of several millimeters in length that occur across the skin (except the palms and soles). Only the head, eyebrows and eyelashes caused stronger hairs: the terminal hair. These can be pigmented.
The spread of the hair prior to puberty in boys and girls are equal: terminal hairs on the head, eyebrows and eyelashes. The rest of the skin is covered with vellus hair.
In and after puberty
At puberty changes a part of the vellus hair into terminal hair. This process is more pronounced in men than in women. The change is especially prominent in the face (in men), the armpits, chest, abdomen and pubic area. Also the arms and legs caused terminal hairs: the man more and more often than women, but this also depends on race.
With age (past the age of 60 years) changes the coat again. Terminal hairs to vellus hair may devalue. Also performs well in a loss of pigmentation.
The function of the hair
In evolution, man's great 'lost'. Only a small proportion of hairs in man has a clear function. To think of the eyelashes and eyebrows (protect the eyes against dust and sweat). Nowadays it is mainly the social function that has hair in the spotlight. In all cultures, having healthy, luxurious hair an advantage in interpersonal contact.