The hair follicle
The hair follicle is a small bulb shaped pit located deep in the scalp and connected to the surface via a small tunnel or shaft. At the bottom of the shaft lies the follicle and that is where the hair is produced. The follicle is supplied with it's own blood supply providing nourishment for producing hair.
Within the follicle is the hair bulb. This is the unit of actively growing hair cells which produce the hair shaft. The lower part of the bulb continuously produces cells and as they grow they push the previously formed cells upwards. As they reach the hair shaft leading to the scalp they begin to change, and they arrange into layers.
The hair color is determined by special cells in the hair bulb that produce the pigment. Called melanin, this pigment can stop being produced as we age or sometimes under stress and thus you get Grey hair.
As the hair is pushed up the shaft the cells die and are compressed to form the hair. This hair above the line of the scalp consists of deal hair cells which is a protein called Keratin and about ten percent water. Keratin is a tough almost indestructible protein which is very resistant to wear and tear.
Each hair follicle has an oil gland and it lubricates the Terminal hair so that it slides from the shaft. Some produce more oil than others and contribute to oily hair. Typically high androgen levels cause more oil production.
Typically the scalp consists of around 100,000 hair follicles. And that hair can be described as thick or thin, coarse or fine. There are two primary factors that determine the coverage that hair gives to the scalp and they are the number of hairs per square centimeter and the thickness of each individual hair. Some individuals may have 50% more or even 50% fewer hair follicles in rare cases. The diameter of the individual hairs also varies and can greatly effect the fullness that the hair appears to have. Women typically have finer hair but much denser hair counts per square centimeter. Men normally have more coarse hair and a lower density. The fullest appearing hair would be large diameter hair coupled with high density. And the thinnest appearing hair would be fine small diameter hair and low density counts.
The shape of the hair, whether it is straight or curly is also determined in the hair follicle. The curl a hair has is determined by it's cross-sectional shape. Hair that exits the follicle in a round or more circular shape is straight and hair that is more flat or elliptical as it exits the hair shaft will be more curly. The shape also effects the amount of shine the hair has, as more round hair will allow the oil to more easily travel down the shaft as it is being formed.