Biologically, there are three different types of hair that is commonly found on the body of the human beings. The three different hair types are: Vellus, terminal and intermediate hairs.
It is the type of hair that does not have any or much cosmetic importance attached to it. These are short, do not grow more than 2 centimeters and are also colourless due to absence of pigmentation.
Shaft of the Vellus hair lack melanin layer and the follicles are generally placed away from sebaceous gland. These hairs are very fine and soft to touch.
Terminal hairs are the type of hair that we are more concerned while discussing about the problem of hair fall or hair loss from the scalp region. These hairs grow on the scalp and may be sometimes even on the body, in case of some people. The hair follicles of the terminal hairs are placed adjacent to sebaceous glands and the hair fiber is dark with medulla as the inner most part of the hair shaft.
The type of hair that shows the characteristic of both terminal hair and Vellus hair is called the intermediate hair. These hairs are less pigmented in comparison to that of the terminal hairs, but intermediate hair do have a medulla as is case with terminal hair. In a person who is suffering from hair loss or baldness, follicles of both, terminal hair and intermediate hair fail to produce new terminal hair, rather they start producing Vellus hairs.