Permanent hair removal consists of “long-term” hair removal. His promise? Destroy the coat. Yes, but then, how does the laser act on the skin and can the practice be dangerous? Answers with Doctor Isabelle Catoni, dermatologist.

How does the laser work on the skin?

The laser is a beam of  photons called lights . Light always acts on a particular target depending on the wavelength we choose. The wavelengths likely to act on the hair are between 700 and 1100 nanometers. Lasers that can act on the colored part of a hair, the one to which the laser will be attracted, are alexandrites , diodes and Yag . The light then turns into heat and this heat destroys its target .

Over time, have lasers evolved?

There are three differences that make modern lasers more optimal than those before. Today’s lasers benefit from a very efficient cooling system. At the same time as the hot laser shot, a spray of cold gas is sent to protect the epidermis and not to burn it. The laser beam can therefore reach the dermis where the roots of the hairs to be destroyed are located.

Other efficient cooling systems are also used: forced cold air or metal plate. In the past, pulse times were limited to a few milliseconds. Today, there is a wide choice of pulse times which prevent burns and therefore pain. Instead of a single firing time, it is possible to vary the successions of firing which protect against burns. Today, anesthetic creams are sufficiently effective on sensitive areas for laser hair removal to be very bearable.

What is the difference between permanent laser hair removal and pulsed light?

A laser beam is made of all identical photons. A laser is a beam of light in which all the photons of the same wavelength, go in the same direction, in the same direction, like clones.

Flash lamps, pulsed lights, are made up of photons that are wavelengths in different directions and senses. The selectivity is lower, the targets more numerous. Filters are used, depending on the indications to be treated.

The advantages of lamps: they are more effective on fine hairs, they are less painful if they are set correctly. However, they require more sessions than the laser for permanent hair removal.

In terms of permanent hair removal, can we speak of “dangers”?

Practitioners continue to burn skins because of poorly configured devices . Lasers are complex and should be handled by trained professionals!

On the other hand, the laser is not the cause of disease, except for vitiligo , the disease that destroys melanocytes . This can be triggered on an individual who has genetic susceptibility. Too aggressive an action on the skin can trigger it and depigment the skin .

Permanent hair removal, if poorly indicated (in areas not to be lasered), can cause paradoxical stimulation . On some individuals wishing to epilate their fine facial, arm or back hair , we have seen the appearance of real terminal hairs whose cycle is endless. It is therefore advisable to choose areas on which there are only terminal hairs, large hairs and not very fine hairs, hardly visible that there is a risk of stimulating.


It is necessary to take  certain precautions before a laser session  :

  • Avoid waxing before the session: the session is useless if there is no bulb to destroy.
  • The patient should shave 24 or 48 hours before the session.
  • The patient should avoid exposing the areas to be treated to the sun. He will need to apply sunscreen. Otherwise, the session will be postponed for the next 6 weeks, even if the sun exposure has been brief.
  • The patient should know cost of laser treatment or take any products to facilitate tanning at least three weeks before a session. This concerns both direct exposure to the sun and sessions in tanning booths. The laser does not differentiate between melanin in the bulb and that in the skin. The latter thus risks being burnt.
  • The patient and the doctor should wear glasses during the session to protect their eyes.
  • The patient should apply sunscreen before and between sessions. Otherwise, the sessions must be postponed to avoid any risk of burning the skin.


Permanent laser hair removal  is contraindicated in certain cases:

  • When the patient is taking photosensitizing treatment (certain antibiotics such as Ciflox, Oflocet, Peflacine, Bactrim or tetracycline ink and certain anti-allergics such as Mequitazine or Promethazine). This can cause burns to the skin.
  • When the patient has slightly tanned skin. A slight exposure to the sun is enough to postpone the session.
  • When there is a tattoo on the area to be waxed. Indeed, the laser will destroy the dark pigment of the skin, which can lead to burns.
  • When a lesion is present in the area to be treated. You have to wait until the skin is completely healed so that laser hair removal can be performed.
  • Laser hair removal is contraindicated on areas with only light down. Indeed, a fine and clear down contains very little melanin and cannot concentrate the heat of the laser at the level of the root. There is also a risk of biostimulation of the down following the use of the laser.
  • Moles in high concentration on the area to be treated are a contraindication. This is because the laser beam can cause degeneration if it is directed at a mole. The latter must therefore be bypassed, and if this is not possible, the doctor cannot perform an intervention.



The results of permanent laser hair removal are best when performed after 25 years in women and 35 years in men. From this age, permanent laser hair removal can significantly improve patient comfort. The latter are no longer obliged to shave every morning or to wax every two weeks. Results are usually final, but exceptions may exist. In the event that laser hair removal has not made it possible to obtain visible results for sessions spaced three months apart, the treatment is generally postponed for a few years. It should be noted that results vary from patient to patient. In addition, the results are visible from the first session, but you have to wait at least 4 sessions to obtain an aesthetic appearance. About 5 to 7 sessions are necessary to obtain a satisfactory result. About 30% of the  hairs are eliminated at each session.


You May Also Like

The most common skin problems, according to age and time of year

It is estimated that dermatologists receive more than 600,000 consultations each month…

REVIEW: Spider-Man: Miles Morales (2020)

IMAGE: Spider-Man: Mile Moral (2020) Video Game Ratings Transferring a superhero’s coat…

17 questions for your future SEO professional

What questions would you ask your new SEO specialist? What to do if…

Scientists explain cultural differences using rice theory

Beijing – The different methods of growing rice and wheat may have…