As we know hair is basically skin continuation in form of the thin thread-like outgrowthes from the scalp. Hair serve both humans and animals for protection against external environment. In humans, development of hair follicles first begins on the head, particularly on the eyebrows along with the lower and upper lip of an embryo. From these first few hair follicles on the face, the development of the hair follicles gradually expands symmetrically to cover the entire embryo save for the palms of the hands and soles of the feet. Skin areas further away from the head, especially those on the limb extremities, take longer to develop embryonic hair follicles. It can take up to 110 days before hair follicles can be seen to start developing on the arms and legs.  

 

The developing in mother's womb baby has by third month the hair-like fuzz. At the same time begin to form hair follicles that will produce the hair throughout the life the person after birth. Shortly before the birth of a baby or shortly after it the newborn fluff disappears and its place is taken by substitute thin, but real hair. It was determined that some of the deviations of the health of pregnant women can affect the appearance of various pathologies of hair or its balding in later child's adolescence or youth period. During puberty besides the head, eyelashes and eyebrows, hair start to grow in arm pits, on the genitals, for men in addition on the chest and face (woman'body usually covered with less hair than man's). Over the time, older men observe enhanced growth of hair in nose and ears, and some women begin to grow stronger hair on their faces. The average diameter of the hair is 80-120 microns, depending on the location and physiology. The diameter of an atom of hair cells is 0.000 000 000 1 m, ie one cell has on average from 80,000 to 120,000 atoms. Depending on the shape of hair, number of atoms of hair cells can vary between 500,000,000,000 and 1,000,000,000,000.

Hair appearance is always caused by a sudden proliferation of cells in the embryonic layer of the epidermis (outer layer of skin), ie hair embryo cell begins to divide and grow into the skin tissue. This proliferation of hair cells is called the "hair beginning", and the tiny "tongue" of this proliferation of cells goes into skin tissue, forming a channel (a hair bag or pocket), which than reaches a certain depth in the skin tissue and formes a dermal papilla by the accumulation of cells. 

 

The very first stages of hair follicle embryogenesis are shown in the picture above. At stage A, before hair follicle development, the epidermis and dermis are uniform. At stage B, a few dermal fibroblast-like cells aggregate below the epidermis and the epidermal cells above the aggregation become larger. At stage C the epidermal cells start proliferating and push down into the dermis following the dermal papilla cells.