Hair covers all parts of the human body at varying rates, with the exception of the palms of hands, soles of the feet and lips. Hair is seen more clearly on the scalp, face, including nose and ears (in some cases), armpit, pubic area, chest and legs.
Facts about Hair Follicles
Hair follicles are the part from which hair grows and they are small bumps in the form of a cup hidden deep in the fatty layer of the scalp. Hair follicles are well equipped with blood vessels, and blood circulation through them feeds the growing area. Hair follicles have the same normal temperature of the human body and are not affected by hot or cold water.
Hair Growth in Animals
Hair grows at varying rates depending on the amount of exposure to natural light, which changes successively depending on the season of the year. For example, hair grows faster in winter when the days are short. It is supposed that the nature of human hair is similar to this, as hair grows slightly faster in winter. Hair follicles consist of two divided areas: hair root and hair shaft.
How many hairs are there in the human head?
• On average, the head of a person contains about 100,000 hair follicles. Some people may have 150,000 or more hair follicles.
• On the baby's head, there are about 1,100 follicles per square cm, and decreases gradually to reach 600 follicles at the age of 25 years, but that number depends on the physical condition of the person.
• In the ages between 30 and 50 years, the number of hair follicles decreases further to reach 250-300. After this stage, slight hair loss starts as the person ages.
• Each hair follicle develops about 20 new hairs in life. Each new hair grows for several years, and could be more than one meter long.
• Each hair falls out eventually, and is replaced with a new one.
Hair root exists inside the hair follicle. It is made up of active cells, which eventually produce a high and long cylinder, the hair shaft. The process of producing new cells continues at a consistent rate at the bottom of the hair root. While these new cells grow and evolve individually, they push up previously formed cells. When cells reach the upper part of the hair root, they begin to change and become six cylindrical layers, each one inside the other. The three inner layers of the cells form the actual hair while the outer three layers constitute the lining of the hair follicle. The dye, known as melanin, responsible for coloring the hair is produced by special hair cells called pigment cells. While hair grows up inside hair follicles, the melanin is transformed up in the inner part of the hair.
The central area of the hair follicle
The central area of the hair follicle is the area where the active cells die and harden to form what we call the hair. While the lower cells continue to divide and push upwards, the hair grows upwards, and finally comes out of the skin. It now consists of a mixture of different forms of special hair protein, known as keratin. Some of these keratins contain a high percentage of sulfur, and some have less. Sulfur plays an important role in hair styles, especially when using cosmetic treatments.
What is the hair shaft?
It is part of the hair that can be seen above the scalp. It consists primarily of dead cells that turned into keratins and necessary elements for their cohesion, along with small amounts of water. The lubrication of hair ends is done by natural oil (called sebum) which is produced by the sebaceous glands inside hair follicles. The amount of sebum produced by the sebaceous glands is often determined by genetic genes. However, the sebaceous glands of men and women at high levels of hormones (androgens) tend to produce more fatty substances. In many teens, the dramatic increase of hormone levels, which in turn leads to the production of fatty substances, produces tendencies to oily hair, a very common phenomenon among many young people. The good news is that most of them outgrow it.
The Structure of the Hair Shaft
A smooth glossy hair has a more complex structure than one might imagine. Comparing hair to tree, the complete humidification lies in the center of the tree behind a solid protective layer of the outer bark. If the "bark" of the hair is in good condition, the whole hair will be in good condition. Yet if the "bark" is stripped and the central part of the hair is revealed, then the hair will be cut. This central part of the hair is called the cortex, which makes up most of the hair shaft. The cortex is the part that gives the hair its special qualities such as flexibility and curliness. The cortex has plenty of keratin filaments that stretch along hair. These keratin filaments consist of keratins containing a small amount of sulfur. These filaments are compressed to form larger bundles of fibers which are forged together by keratins that are rich in sulfur and intercellular tissue. The resulting mixture between the fibers and the intercellular tissue is extremely strong and resists tensile and other forms of stress, such as sprains, as does the mixture of resin and fiberglass that is used in the construction of many boats.