2 - Cosmetics and hair and nails

Abstract

This chapter explores the generation and types of hair, and the function of nails. Hair and nails are actually modified epidermal cells, so these are called skin appendages along with sweat glands and sebaceous glands. Human hair structures develop between 9 weeks and 4 months after conception. All hair structures of the human embryo are formed in sequence from the head down to the caudal part of the body. On the head, the first hair structures are formed in corresponding sequence at the eyebrows, the top lip, and the lower chin, then, on the scalp and face and finally on the other parts of the head. The hair is classified into two types: terminal hair and vellus hair. Terminal hair may be either long or short. Depending on the location, vellus hair changes to terminal hair when puberty is reached. This chapter further describes that nails are a very tough sheet of keratin growing from the epidermis of the dorsal surface of the toes and fingers. They are another form of skin appendages. Nails protect the distal tips of the fingers and toes, enable the fingers to grasp very fine objects as well as increase the strength of the fingers and toes.