The hair on our body can be classified into two types: Vellus hair and Terminal hair. Vellus hair is the fine hair that covers most of our body except our hands and feet. Terminal hair, on the other hand, grows on our head, underarms, and genital region.
The structure of hair is made up of three layers: the Cuticle, Cortex, and Medulla. The Cuticle is the outer layer that varies in thickness based on one’s ethnicity. Caucasian hair typically has 4-7 layers, Asian hair has 11 layers, and African hair has 7-11 layers. The finer the hair, the fewer cuticle layers it has, and the coarser the hair, the more cuticle layers.
The Cortex is the middle layer that determines the hair’s color, strength, and texture. It contains keratin filaments held together by hydrogen and disulphide bonds and contains the pigments pheomelanin (red and yellow) and eumelanin (black and brown).
The Medulla is the soft and fragile core of the hair shaft and is not essential for hair growth. Some people, especially those with finer hair, may not even have a medulla.
The chemical composition of hair includes carbon, hydrogen, nitrogen, sulfur, and oxygen.
Hair growth occurs in three stages: Anagen (active growth), Catagen (transitional phase), and Telogen (resting phase). The Anagen stage can last from 1.5 to 7 years, with the average being 3 years. The Catagen stage lasts for a couple of weeks, and the Telogen stage lasts for 3-4 months. The cycle then repeats, with new hair growth pushing out the old hair. It’s normal to lose 100 hairs a day through natural shedding, brushing, and other activities.