Hair Biology


Hair follicle is formed in the upper layer of the skin from a cluster of cells called primitive hair germ. The primitive hair germ cells get their nourishment by working their way down into the dermal layer of the skin. This cluster of cells creates a follicle, which creates a pocket known as the root sheath as they pull the upper layer down in search for nourishment. Out of this sheath the hair will grow. Hair grows from stem cells. These cells grow directly under the oil (sebaceous) glands. As the cells continue to grow, the nucleus of the cells disappears and the cells become keratinized. (dead cells; hair)

Your hair follicle consists of 3 important parts;

1.      Sebaceous gland
which  produces sebum, a kind of oily substance that is responsible for protecting your hair from becoming dry, brittle and cracked. And also inhibits growth of microorganism on the skin. However, the glands can either overproduce sebum that can cause oily scalp or under produce sebum.

2.      Blood and lymph vessels
which are your energy and nutrient supply line to the skin and hair follicles. This supply will be disconnected from your hair follicle when it reaches the CATAGEN phase. (see hair growth)

3.      Arrector Pili muscle
which is attached to your hair follicle is responsible for making your hair stands up when you have goose bumps. It also functions by raising the hair to catch the heat to keep you warm. Stem cells at the junction of this muscle and your hair follicle are responsible for the ongoing hair production during the ANAGEN phase. (see hair growth)

All hair whether straight, wavy, curly or kinky is composed to two essential parts; the root and the shaft. With the hair shaft having 3 parts:

1. The medulla– contains melanin, responsible for your natural hair color

2. The cortex – the thickest part of the shaft, determines hair’s strength, elasticity and moisture content

3. The cuticle – what we see or think as our hair, contains keratin cells (protein) that lies on the shaft closely together like fish scales

  • The number of layers determines each individual’s hair diameter, thus your hair’s thickness
  • It defines or determines how healthy your hair is;

Healthy hair is defines as having intact cuticle

Unhealthy whether from heat, or chemical processing, is defined as having separated or broken cuticles.

  • Broken cuticles cause the hair’s cortex and medulla to become expose, thus making hair susceptible to breakage


The shape of the hair shaft is determined by the shape of the hair follicle. People with straight or wavy hair have typically round or oval shaped hair follicles, while people with curly or overly curly hair’s follicles are elliptical in shape. How your hair is shaped, is determine by the follicles and giving credits to genetics follicles vary in size, shape and thickness.

The more elliptical the shaft is, the curlier the hair. The cross-sectional shape also determines the amount of shine the hair has. Straighter hair is shinier because sebum from the sebaceous gland (a kind of oily substance that is responsible for protecting your hair from becoming dry, brittle and cracked), can travel down the hair more easily. The curlier the hair, the more difficulty the sebums has traveling down the hair, therefore the drier or dull the hair looks.


It is not the diameter of each stand of hair that defines whether your have thick or fine hair, rather the number of shafts per square inch. In other words, you may have very coarse hair but not a lot of it and be classified as having fine hair and on the other hand one can have fine hair but a lot of it and be classified as having thick hair (See hair type chart).

Whether your hair is straight, wavy, curly, kinky or frizzy, a hair is always a hair because its basic composition is largely based on keratin and is always the same. However the special shape of the hair varies enormously, and hair type you end up with is determined by its cross-sectional shape or the shape of the hair follicle.


Hair growth is approximately 0.5 inches per month, being about 6 inches per year. Cell division is responsible for the hair growth cycle, where the new cells push the hair forward to make it longer, and the new hair is added at the root. There are about 100.000 hairs on a healthy scalp of hair. Each of these hairs will, in normal healthy conditions, last for one up to six years. People lose about 100 hairs per day, in normal conditions. And the fallen hairs are replaced by new hair. During its life a hair goes through three phases of growth: the anagen, the telogen and the catagen.


This is the first phase of your hair growth cycle which is also known as the growing phase with new hair growing in the hair bulb. At any one time, 80 – 90 percent of your hair follicles on your scalp are in the ANAGEN phase. During this period your will hair grows continuously. The growing will continue for 3 to 7 years and will grow at about the rate of half an inch a month (also depends on genetics). During that time, the hair bulb produces your hair pigment and your blood supply provides nutrients and minerals to your hair to make it look thick and nourished.


After the ANAGEN phase, your hair will turn into a transitional phase before going to rest. This short phase is known as the CATAGEN phase which last for 2 to 4 weeks. It is the phase when hair stops growing because the cell division stopped. During this time, your hair detaches from the blood supply and the detached follicle will slowly shrink to about 1/6 its size. During that time, the hair bulb will be pushed upwards towards the surface when the new hair is formed.   Approximately 1 – 2 % of your hair will be in this phase in your scalp.


This is the final phase of your hair growth cycle. It is also known as the resting phase where your hair follicles will slowly fall off and replaced by a new hair. New hair starts growing in the papilla and finally the old hair falls out. Around 10 – 15 % of the hair in your scalp will be in TELOGEN phase, 50 – 100 hairs from this phase will shed daily and this period lasts for 3 months before the hair falls out. The hair follicles become weak and thin and you can easily pull them out – new hair follicle will emerge once the hair the hair falls.


The maximum length to which you can grow your hair is basically a matter of genetics and the type of care it receives. Some people can grow thick, lustrous tresses while still others find that getting their hair to grow past their shoulders is an extraordinary task.  The types of hair products used (harsh chemicals, est.) can also have a tremendous effect on hair growth and length.

The frequency of trimming can as well have an effect on your hair length over a period of time. For example, if your hair averages a four-year ANAGEN phase and you have your hair trimmed one-half inch every three months, you can expect your hair to grow four inches each year, or a total of sixteen inches before it reaches the CATAGEN phase.

And the hair can appear considerably shorter depending on your wave or curl patterns. Once straightens (temporary heat straightening) hair length will be better notice. Your head size, shape and your height all can make your hair appear shorter by comparison to someone else whose hair length measures equal to yours.

Trimming your hair is important in order to keep your end healthy and even, but by using the right products in your hair and with frequent treatment, you will decrease the amount of slit end, and the need for frequent trimming though resulting in longer healthy hair.

However, if have been keeping your hair healthy and have been trying to grow it out for years and you still not getting the length that you desired, keep in mind that the maximum length you can grow your hair is base on genetics and you may not be predisposed to grow your hair as long as you’d hoped.