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    Cycle-pilaire aesthetic medicine bordeaux l'aparté
    Home " The body " Laser hair removal " Phototype and hair cycle: their influence on laser hair removal

    Laser hair removal requires a thorough understanding of hair physiology, and in particular of the hair cycle. This is the way hair grows. Based on this, we can optimize laser hair removal sessions for greater efficiency.

    What is the pilar cycle?

    The hair cycle is the life cycle of the hair. This is the basis for determining the frequency of sessions.

    The number of laser hair removal sessions depends on several factors, especially the hair cycle. Hair goes through several phases. These phases correspond to periods of growth and periods of rest. On a given area, they are all represented, so we have hairs of different ages in that area. There are 3 phases in the hair cycle:

    • The growth or anagen phase, during which the hair grows continuously. Only 10-30% of hairs are in this phase. The bulb is well vascularized and very rich in melanin. The rate of hair growth is around 0.35 mm per day. The duration of this phase varies according to the area. It is during this phase that the laser will be most effective. Indeed, the hair is the laser's vector. Light energy transformed into heat is transmitted to the bulb, the hair manufacturing plant. The bulb is then destroyed, and the hair no longer grows back.
    • The resting phase, or catagen phase, at the end of which the hair falls out under the pressure of new hair formation. This is a short period lasting a few weeks. The laser destroys the hair, but as the hair is not in contact with the bulb, the bulb remains intact. The hair factory will restart when it's its turn.
    • The resting or telogen phase lasts between 3 and 12 months, depending on the area. It culminates in hair loss. In this phase, as in the previous one, the laser burns the hair, but it will grow back.

    The hairs are independent of each other, and the different phases are not synchronized. It therefore takes several laser hair removal sessions to completely remove hair from an area. This is because you have to wait for the hairs in the other 2 phases to fall out and for their hair follicles to produce new hairs. Moreover, from one individual to another and from one area to another, it's impossible to know precisely how many hairs are in each phase. On average, between 10 and 30% are in the anagen phase, which represents a wide variation.

    Hair growth variation parameters

    Hair growth depends on a combination of vascular, hormonal and metabolic systems. An imbalance in any one of these systems causes a change in hair growth - an increase, a stoppage, even a fall. The hair cycle, which is the succession of these three phases, is a permanent balance between growth and loss. One of the hormones with the greatest influence on hair growth is testosterone. Both men and women produce it naturally. Men produce testosterone in greater quantities. It is responsible, among other things, for chin and chest hair.

    Permanent hair removal?

    Laser hair removal can never be described as permanent. It's more a question of long-term hair removal. The body produces hair follicles all the time, and as we've seen, there's no way of knowing how many follicles are affected during a laser hair removal session. We know that after one protocol, around 90% of hair follicles have been destroyed. That's why we recommend 1 or 2 maintenance sessions per year.

    The influence of hair color and skin tone

    The darker the hair, the more melanin it contains, the pigment that absorbs laser energy. Black hair absorbs virtually all the energy delivered by the laser. The lighter the hair, the less melanin it contains, and the less energy it absorbs. This is why white hair cannot be removed by laser, and why hair should not be bleached before laser hair removal. Laser hair removal is more difficult for people with blond hair, and may require slightly more sessions to achieve optimal results.

    Skin tone also has an influence on hair removal.
    Like hair, what makes skin darker or lighter is the melanin produced by melanocytes. So there's competition between hair melanin and skin melanin... which light doesn't care about. In fact, for a laser shot on dark skin with dark hair, the energy will be absorbed by both the skin and the hair. This is where the risk of burns comes in. To mitigate this risk, some lasers can adapt the power of the shot, the duration of the shot, and thus the fluence. It is therefore easier to remove hair from all skin phototypes with a diode laser.

    On the other hand, laser hair removal is not performed on tanned skin. Hair is the same shade, or even lighter, when the skin is richer in melanin. Melanin absorbs light energy much more than hair. The risk of burns is therefore maximal.

    Phototypes

    Skin color Sun sensitivity Melanin quantity Phototype Hair colors Conditions for laser hair removal
      Very white   Highly sensitive. Burns without tanning   No melanin   I Clairs Difficult laser hair removal
    Dark Ideal
      White skin   Highly sensitive to sunlight. Always burns and tans with difficulty   Very little melanin   II Clairs Difficult laser hair removal
    Dark Ideal
      Beige to light brown (light-eyed chestnuts)   Sensitive to the sun. Sometimes burns, but tans.   Little melanin   III Clairs Difficult laser hair removal
    Dark Ideal
      Light to moderate brown   Bronze without burning   Average quantity   IV Clairs Difficult laser hair removal
    Dark Careful laser hair removal
      Brown to dark brown (dark skins, mestizos...)   No sun sensitivity   Large quantities   V Dark Take care, keep out of the sun as much as possible
      Black skin   No sun sensitivity   Large quantities   VI Dark Caution +++. Low energy.

    In conclusion

    The number of sessions is therefore the age-old question of laser hair removal. The inter-individual parameters of hair growth and other factors are so numerous that it's difficult to give a precise number of laser hair removal sessions. So it's best toadapt to each patient and his or her hair regrowth.
    Light skin with dark hair is ideal for hair removal. However, there are lasers that can remove hair from black skin, such as Nd-Yag. But for tanned patients with light hair, it's best to wait between 2 and 4 months, depending on phototype, after the last exposure to the sun, before having a laser hair removal session.
    Above all, we're not talking about permanent hair removal, but long-lasting hair removal.

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