When approaching the topic of hair chemistry, one may think about the question, where does hair come from? Saclike holes called follicles are located all over the human body. At the bottom of these follicles are a cluster of papilla responsible for the growth of hair. As the papilla, otherwise known as hair bulbs reproduce to make new hair cells, the old ones are pushed up towards the surface of the skin causing the hair to grow longer. This may seem like a simple concept to grasp.
However, the process of hair growth is a little more in depth.
Hair growth takes place in three phases the anogen phase, the catagen phase, and the telogen phase. The first phase to take place, the anogen stage, can last anywhere from three to seven years. During this stage, hair grows at an average rate of 1 centimeter per month which adds up to around 12 centimeters or 1 inch per year. It is also during this stage that melanin, the pigment that gives hair color, is created. As people get older, follicles gradually give up producing thick, strong hair. As a result, hair becomes thinner and shorter; baldness may even occur. The next phase in hair growth is the catagen phase which takes place anywhere from two to four weeks. During this stage, the base of the follicle moves from underneath the skin to the face and rests near the opening of the sebaceous duct until it is ready to begin growing. This growing takes place during the telogen phase which lasts anywhere from three to four months. During this stage, new hair begins to grow from the hair follicle. As it grows upwards, the old hair will be shed naturally or may be pulled out. This shedding of telogen hairs happens easily and painlessly; these are the hairs that fall out when a person is shampooing or brushing his or her hair. As each hair is released, the process starts all over again.
An important fact to consider when thinking about these three stages is that they are independent in each hair follicle. For example, while one hair follicle is in the catagen phase, another hair may be released because the follicle is in the telogen phase. Generally in humans, about 85% of hair is in the anagen (growing) phase, about 12% of hair is in the telogen (shedding) phase, and about 3% of hair is in the catagen (resting) phase.
Aside from hair growth, the follicle also contributes to determining the thickness and texture of hair. The shape of the follicle gives the hair it produces texture and thickness. For example, a large circular follicle will produce straight, thick hair, whereas, a thin, oval follicle will produce thin, curly hair. When studying each strand of hair, one will learn that each hair shaft contains two or three layers: the cuticle, the cortex, and sometimes, the medulla.The cuticle is the outermost layer of the hair shaft that is made of cells that overlap and protect the inner layers. The next level is the cortex which is made out of long keratin proteins that “twist like the curly cord on a...