Until then we have enough time to study and understand the life of hair. Hair is actually dead material when it leaves the root - otherwise it would hurt when your hairdresser cut it. A blonde head of hair has usually much more fibers than red or dark haired heads. Hair consists mainly of keratin, which is also responsible for the elasticity of fingernails. A single hair has a thickness of 0.02-0.04mm, so that 20 to 50 hair fibers next to each other make one millimeter.
Hair is strong as a wire of iron.
The root of a hair fiber sticks in something like a bag in the skin. The fiber is pushed out of this bag about 0.35mm per day, making an average growth rate of 1cm, or half of an inch, per month. The growth rate is however very much related to the individual person, his age, his diet etc. Healthy hair has an average lifetime of 2-6 years. After a rest period of three months the single hair falls out, and a new fiber starts to grow out of the bag.