The hair that you see on your head and skin is dead tissue. Hair is derived from a structure in the skin called the hair follicle. The only part of the hair that is alive is the portion that comes directly from the follicles in the dermis (skin) but once that part reaches the surface, it is considered dead. It appears to be growing because the new growth from the follicle pushes up the strand of hair that is already on the surface.
Almost all hair strands that are found on your head are made up of 3 basic structures, the Cuticle, the Cortex and the Medulla.
The cuticle is the outermost layer of the hair shaft and it is a transparent to translucent structure that protects the inner structures of the hair. The cuticles are similar to scales on a fish and change direction depending on the pH of the surrounding area. They begin to open in an acidic medium and close in one which is alkaline. The cuticle layer can become damaged or destroyed if the medium is either too acidic or too alkaline. The normal pH of human hair is between 4.5 and 5.5 on the pH scale.
The cortex is found just under the cuticle. It is the part of the hair which is made up of keratin, a protein found in the hair. It makes up the bulk of the hair strand and is responsible for absorbing water as well as giving the hair strand its flexibility and strength. It also contains melanin which determines the colour of your hair.
The medulla is the innermost part of the hair structure and is not always present. It is made up of large, loosely connected cells. It is partially responsible for the shine and colour undertones of the strands. That is why hair colour appears different when in sunlight.