The hair emerges from the scalp follicular units, each containing up to four hairs and, on average only 20% contain one, 45% contain two, 30% contain three, and 10% contain four hairs. This proportion is variable from person to person and according to the age and gender.
All different hair body go through cycles of growth, rest and fall.
The hair begins its life cycle by the anagen (growth) growing from 1 to 2 cm per month, in the head during 2-6 years, longest in women than in men. In other parts of the body we have a shorter growth phases; therefore, the hair, never reachs the length of the hair of the head.
Follows the catagen phase (resting) that lasts from 2 to 6 weeks, in which the hair begins to want to loosen the follicle.
Finally comes the telogen (hair loss) in which the hair falls and the roots remain at rest, occurring for 2 to 4 months. During this period, the hair is pushed out of the follicle, as a new hair is being born, by starting again the anagen phase.
Capillary density is one of the most important factors when assessing a patient's hair transplant potential, it is crucial to define the amount of hair to be transplanted.
Typically, the average density is between 100 and 140 hairs per cm 2, whereby a hair transplant of 60 hairs per cm2 could provide for a similar aspect that the patient had in the past.
If the donor site of the patient in the occipital and temporal regions, has a strong and dark hair consistently and possibly wavy hair, we can obtain best results with less follicles. On the contrary, if your hair is thin, blond, weak and your donor area is getting increasingly reduced, it will only be possible to partially solve your problem.
We can not forget that the donor area is limited, with between 4,000 and 7,500 follicular units available, ie, 5500-15000 hair units, which limits the effect of any hair transplant.
Every day, we lose 50-100 hairs but fortunately most of that hair grows back, since the follicles remain intact and healthy.
It is necessary that the hair loss or decrease reaches 50% of the total number of hairs, for being noticeable to the human eye, and so, we will need only half of the original density for the patient to stick with the same look of the past.