The colour of hair, its shape and quantity varies from individual to individual. Some have black hair, some red, some blonde, curly, straight, thick and thin. All these characteristics are determined by genetic or racial factors.

Straight hair is round in cross-section and arises more or less perpendicular to the skin surface. Curly hair is oval and grows out at an angle, twisting and curling as it grows, Each type has its advantages and disadvantages.

Straight hair is easy to manage, but rather ordinary looking. This is why people like to wave their hair. Curly hair is attractive but not when the curls are too tight. Tightly curled hair is very difficult to manage and this is one reason why some people have their hair straightened. Curly hair may sometimes turn back on itself and grow back into the skin, or it may puncture the follicle instead of growing out. The hair is said to be in-grown. In-grown hairs irritate the skin, causing it to become inflamed. They usually occur over the back of the neck where pressure from collars encourage hairs to turn back into the skin.

Another very rare type of hair is known as woolly hair it feels and looks like wool. Woolly hair is flat or kidney shape in cross-section. Hair colour is determined in a complex manner by the genes we inherit from our parents. It has mostly to do with the melanin (a skin pigment) in hair. There are two types of melanin: eumelanin, which is black and gives black or brown hair; and phaemelanin, which is red or yellow and gives auburn or blonde hair. However, the ultimate colour of hair depends not only on the type of melanin, but also the shape and position of the melanin granules within the hair and the way air bubbles within the cortex refract light.

Asians and blacks have black hair while Caucasians have a wide variety of hair colours. The colour, thickness and quantity of hair are inter-related. Light-coloured hair such as blonde hair is finer and denser whereas red and black hair is thicker but less dense.

The number of hair follicles and hair decreases as a person ages. An adult scalp 20-30 years old has about 615 follicles per square centimeter of scalp. This falls to about 485 when the person is 30-50 years old, and 435 when the person is 80-90 years old.

As the number of follicles decrease, so will the number of hairs. Therefore, it is normal for hair to thin as we grow older and there is no treatment that will permanently reverse this process.