Generality
The number of hairs on the head varies greatly from person to person, influenced as it is by numerous factors, such as age, sex, genetics, eating habits, lifestyle and state of health in general.
However, it is estimated that on average there are about 100, 000 hairs on the head of each individual. In truth, the number of hairs on a person's head is affected by their color. Indeed, it has been estimated that:
- Individuals with blond hair possess about 140, 000;
- Individuals with red hair own about 80, 000;
- Individuals with brown or dark hair have about 100, 000.
Furthermore, the hair color also seems to be related to the thickness of the hair. In fact, generally speaking, blond hair tends to be thinner than brown or black hair.
Of all these hairs on our heads, around 90% are in a growth phase. During this period the hair stretches an average of 1-1.5 cm per month.
Therefore, we can play around with a curious mathematical calculation: every year the hair follicles of a person produce, as a whole, something like 15 kilometers of hair.
Hair growth
In the life cycle of a hair the growth phase (anagen) normally lasts from 2 to 6 years, followed by a transition period (catagen) in which the hair stops growing and the follicle rises towards the skin surface. This phase, lasting 3-4 weeks, precedes a last resting period (telogen) of about three months, at the end of which the follicle is reactivated producing a new hair that causes the old hair to fall.
As the age progresses, the duration of the anagen phase is reduced; consequently hair growth slows down.
Hair loss
Normally, a fall of 40-100 hairs per day is considered normal and completely physiological. However, when this number increases, it is appropriate to worry and ask the advice of your doctor (to learn more: How many hairs fall in one day?).
Excluding external factors that can promote hair loss, one of the main causes responsible for this phenomenon is certainly the well-known and widespread androgenetic alopecia.
In the wake of the extensive incidence of this form of alopecia - which affects about 80% of men and 50% of women over the course of their lives - the follicles in the telogen phase become proportionately more numerous. In the final stage of this process the hair becomes very similar to that of the newborn: short, thin, almost transparent. The hair, therefore, does not fall, but becomes so thin and short as to be imperceptible. Moreover, androgenetic alopecia considerably decreases the number of terminal hairs in the frontal and vertex areas, while it saves the follicles present in the region of the temples and the nape of the neck, giving the head the classic "crown" appearance.
