The hair growth process starts in the womb, the five millions or so hair follicles which produce hair on the scalp, face, legs and all of the body parts except the soles of the feet and the palms of the hand are formed before birth. The hair is “dead” due to its non-living nature. Because it is “dead”, it can be cut, tied, heated and treated without causing pain. In fact, the hair continues to grow since in the womb. It grows until the bulb within the skin loosens its grip and eventually releases the hair and where the balding begins.
The growth cycles of hair starts before birth and continues throughout the entire life. There are 3 types of hairs in the growth cycles:
- the first form of hairs which are fine, unpigmented lanugo hairs, usually shed seven to eight months after conception.
- the second form is vellus hair, a fine, downy hair covering the bodies of children.
- the third is the terminal hair where vellus hair become thickens and pigmented, turning into secondary or terminal hair, normally found on the head, armpits, pubic region, and in males, on the chest, arms and legs.
The Hair Growth Cycles
The hair growth is cyclical with three phases:
- rest (telogen);
- growth (anagen) and
- a short time between the two called catagen.
The anagen period is the active growth period which cover averages 1 000 days or three years. But it can last anything from weeks as in hair on the finger or to six or seven years as in the hair on a woman’s scalp.
The length of the hair is determined by the duration of this active phase and by the speed of growth. Numerous studies have measured the rate of hair growth. These measurements include:
- Hair on female thigh: 0.24 mm over 24 hours
- Hair on male chin: 0.38 mm over 24 hours
During catagen period which lasts for a period of a few days, the follicle shrinks and the hair moves away from the dermal papilla up towards the skin surface.
This is the rest period of the hair growth, lasting about 100 days or a few months. The fully formed hair remains firmed in the follicle, but separated from the dermal papilla. Finally the hair becomes loose and is shed. But before it falls out a mission of ‘germ’ cells heads for the dermal papilla, the original site of growth, taking with it the potential to form another follicle and another hair. So when an old hair is shed, there is another already in production to replace.
At any period of the hair growth cycle, the hair follicles on the scalp may be in all of these phases concurrently. Some hairs may be growing, some about to fall out. The s growth is both continuous and random. In an average scalp follicle count of 100 000, one hundred are at the end of their cycle and about to shed the hair. So it’s absolutely normal to lose hair daily from combing and washing.
There are two appendages accompany the follicle in its life-long work such as the arrector pili muscle and the sebaceous gland.
- The arrector pili muscle is a remnant of hairier days when pulling the hairs upright could help humans keep warm, like other furry beasts
- The sebaceous gland, tucked in at the side of the follicle, pumps out sebum — a natural oil which coats each hair, keeping it waterproof and supple. The hair bulb is fed by a knot of capillaries of blood.
Hair gets its color from pigments found in the cortex. Melanin (black/brown) and phaeomelanin (red/yellow) are the two major ones. The precise color depends on the mixture of these two colors. The pigments are found in the cortex and medulla in ovoid or spherical granules.
The pigments are made by melanocytes, the same cells responsible for producing a tan in the skin. They are found in the upper section of the hair bulb and transfer color to keratinocyte cells. The greasy or dryness of the hair of a person relates to the sebum level which depends on the activity of the sebaceous gland.