The hair is made up of keratin , a protein based substance. Each hair consists of three layers. The outermost layer, known as cuticle , consists of hundreds of tiny, overlapping scales. The middle layer, known as the cortex , consists of long thin cells which give the hair its elasticity and colour. The innermost layer, known as medulla , is made up of spongy tissues which may contain some colour pigment.
Hair is formed in very small tiny pockets in the skin, called follicles .
An upgrowth at the base of the follicle, called the papilla , actually produces hair, while a special group of cells turns amino acids into keratin . The rate of production of these protein building blocks determines hair growth. The average growth rate is about 1.2 cm per month, growing fastest on women between the age group of 15 to 30 years. The sebaceous gland which secretes the oil that gives healthy hair its natural shine is located half way along the hair follicle. It is the pattern of cell growth at the papilla which determines whether hair growth is straight, wavy or curly.