Laser hair removal is becoming more and more common in aesthetic procedures. More than 40% of women worldwide report problems with unwanted hair.
Why is it possible to wax or reduce hair with lasers or pulsed light?
The bulb of the hairs -root- is where there is the greatest amount of melanin, the pigment of the skin and hair, which is what gives color to both of them. The melanin that gives color to our skin is in the epidermis, the most superficial layer of the skin. The melanin of the bulb of the follicles is noticeably deeper, in the dermis. This melanin of the bulb, ideally, is darker than the epidermal melanin, whose concentration and size give us a specific skin color and the ability to tan.
Both lasers and intense pulsed light (IPL) are light systems that, from the outside, can emit a beam of light that impacts a specific skin structure without the rest of the surrounding skin having any consequences. The skin structure that absorbs this light selectively and with greater affinity than the rest of the skin is called chromophore. Melanin is one of the main chromophores of the skin and when we shoot on it we can depilate -if we do it deeply- or treat spots -superficial melanin-. The other chromophores of the skin are hemoglobin (which circulates inside the capillaries and is where we shoot when we want to eliminate blood vessels or redness) and water. When we heat the water in the skin we stimulate the production of collagen (we improve signs of aging and scars) or we destroy benign skin lesions that we want to eliminate through a delicate burn.
Thus, if we manage to get a device to get light to reach the melanin of the follicular bulb and for it to absorb the energy and burn without damaging the rest of the skin, we will be doing selective damage to the hair and, consequently, we will be waxing from the root of the hair.
The beam of light absorbed by the follicular bulb is able to heat it up so much that it destroys or weakens it definitively.
As you may have already thought, it is necessary for light to travel from the outside, cross the epidermal melanin without damaging it, and destroy the melanin in the hair. And it is precisely at this point where the difficulty of hair removal with light systems lies: if part of the energy is absorbed in the epidermal melanin accidentally instead of in the follicular bulb, unwanted effects can appear.
Why is laser hair removal more effective and easier when there is coarse black hair?
Because this hair has a higher concentration of eumelanin, which is darker, and captures the energy of the light devices better. In this way, it heats up more easily and the bulb is destroyed with fewer sessions. And vice versa, hair that is blond or red and fine, has a higher concentration of pheomelanin, which is lighter and absorbs less light from the devices.
How do we get a laser or pulsed light to cross the epidermal melanin without seeing it and reach the root of the follicular bulb?
There are different ways to try to make the melanin in the epidermis as invisible as possible to laser or IPL light:
1. Maximize the difference in intensity between skin color and hair color. If your skin is very light and has very dark hair, it is easier for all the laser energy to be concentrated on the hair and not on the epidermis. For this reason, it is simpler, safer and more efficient to wax for people with very light skin and dark and thick hair. It is for this reason that it is recommended to wax with a laser when you are not tanning (in this case, there is a higher intensity of melanin in the epidermis that will act as a screen for the laser light to penetrate safely). Also for this reason, hair dyes are sometimes used in order to increase their dark color and make them more visible to the laser light.
2. Use lighting systems that reach deeply. If we emit a light that reaches a greater depth in the skin, it is easier for it to impact the melanin of the bulb (in the deep dermis) than the epidermal melanin. We can regulate the depth of the light from a laser by handling different parameters of the laser. The main one, however, is the wavelength. The wavelength, expressed in nanometers, is how long the stride of an electromagnetic wave is: in other words, how deep the laser light can reach inside the skin. The longer the stride, the more distance is traveled per unit of time. Thus, with long-wavelength lasers, it is easier to reach the bulb of the hair and overcome the epidermal melanin. Therefore, lasers with a longer wavelength are safer and more efficient. In addition, there are other parameters that can cause light to reach greater depths in addition to wavelength: pulse duration and creep. Just as wavelength is analogous to the distance of each runner’s stride, pulse duration would be how long the runner is running, and creep would be the energy the runner has to expend to exhaust himself. Indeed, the longer the pulse duration and creep, the deeper the light will reach the skin and the less likely it is to stay on the epidermal surface. Therefore, longer pulse duration and higher creep can increase the efficiency and safety of laser hair removal.
3. Cool the epidermal surface. All lighting systems act by selectively increasing the temperature of the structure that we want to destroy by means of a beam of light (selective photothermolysis). Thus, if we cool the epidermis with ice or with the cooled sapphire of the laser head, it will be very difficult for the epidermal melanin to increase its temperature and, consequently, to be destroyed. By applying cold we increase the safety of laser hair removal.
4. Covering the melanin that we do not want to treat with a white pencil. If we want something to become invisible to the hair removal laser, we must remove 100% of the dark coloration. The lightest color is white. For this reason, to preserve normal moles and freckles (melanocytic nevus) and not accidentally burn them, before the laser hair removal session we must cover them with a white pencil. This practice is an index of the quality of the center that performs hair removal with light systems, because it means that the staff in charge of it knows that normal moles should not be burned (you have more information here).
What is the theoretical difference between laser hair removal and photoepilation?
Photoepilation is performed with a light device called intense pulsed light. Laser hair removal is performed with lasers. Although there are several differences between the two types of devices, the main one between a laser and a pulsed light is that the former emits a single wavelength and pulsed light emits a range of wavelengths.
Let’s give an example to better understand what this implies. Let’s imagine that you are listening to the radio. Your favorite program is on the station that is on the 96.5 FM dial. The wavelength would be the dial (96.5 FM) and your favorite program would be what we want to destroy on the skin (chromophore). In this case, the melanin in the hair.
Metaphorically, a laser would broadcast only your favorite program from the 96.5 FM station every time you turn it on. Once running, you can adjust other parameters, such as volume, bass, treble… to perfectly hear your program (impact more finely on the selected chromophore).
A pulsed light, on the other hand, emits different wavelengths at the same time. In the case of radio, it would be like having several stations on simultaneously: there is your favorite program but also the news, sports, advertising… playing in unison. This allows you to listen to a lot of information at once, but if you want to focus on your specific program, you have to eliminate the other stations (wavelengths) using something we call filters. These manage to stick all those stations to a range of dials where you have a good chance of finding your favorite program without hearing much background noise. In other words: we filter the pulsed light so that the emission of the light beam is as specific as possible to impact the hair without other structures (chromophores) being damaged in the process.
What practical difference does the use of a laser and a pulsed light have, then?
A laser is somewhat more specific and less versatile: it does few tasks at a high level. By adjusting the parameters well, it is very unlikely that the chromophore you are interested in will not be treated properly without the rest of the skin knowing. However, for the health center that owns it, it is a less cost-effective device because it can be used in more specific indications.
A pulsed light is more versatile and less specific: it can treat different skin disorders by impacting on different chromophores, but with the drawback that these chromophores compete with each other and that you can accidentally shoot melanin when you wanted to treat hemoglobin. By handling the parameters and filters we mentioned, a pulsed light can do a very specific job at a high level, too. In addition, it is a very versatile device: you can treat a large number of patients with different problems with a single light system.
Is laser hair removal or photoepilation better?
Each has its advantages. In general terms, however, laser hair removal is considered to be the gold standard (what other systems compare to).
Hair removal lasers are designed with a single, long wavelength that allows them to go deep to treat the hair and give the epidermis minimal risk of suffering. The most commonly used are alexandrite (755 nm), diode (810 nm) and Nd:YAG (1,064 nm). Note that they have different wavelengths from each other: this allows each one to reach a specific depth. These wavelengths are considered ideal for reaching exactly the depth of the hair root without injuring the epidermis.
Pulsed hair removal lights work with filters that restrict wavelengths approximately between 600 and 1200 nm. Note that they contain precisely the wavelengths of hair removal lasers. However, instead of emitting only at 755 nm, it simultaneously fires a light ranging from 600 to 1200 nm. This means that the theoretical probability that a wavelength of 600 nm (which penetrates little) damages the epidermis is greater than if it emitted only at 755 nm. And also that wavelengths above 1,064 nm provide little clinically except for heating the skin.
Of course, all this is determined by the parameters that are selected on the device: you can make a mess with the best laser that exists or a work of art with a well-managed pulsed light.
Lasers are usually systems with faster firing than pulsed lights, and usually have built-in epidermal cooling means (sapphire or cryogen head). However, pulsed lights usually have a head that covers more area per shot and therefore fewer shots are fired per treatment.
How important is it that hair removal is done with different wavelengths?
Although the depth to which a light reaches depends primarily on its wavelength, by handling other parameters (pulse duration, fluence, spot size) we can also vary the range of that beam.
On the theory with a single wavelength we can perform a very correct hair removal, although in certain circumstances it is interesting to have different wavelengths. For example, in very dark skin, to gain safety, it is better to use an Nd:YAG laser. On the other hand, in very light skin with fine hair, it may be more appropriate to use an Alexandrite laser.
It should also be noted that, in the same person, there are hairs of different shades, depth and diameter. By using lasers that sequentially emit three wavelengths (e.g., 755, 810 and 1,064 nm) in one shot, we can cover the entire spectrum of hairs that a patient may have. Or we can also use a specific wavelength in an area of light, fine hair, and another in an area of thicker, more pigmented hair. Another virtue of using lasers that emit different wavelengths in a train of pulses is that pain decreases: instead of having to take three shots each with a different wavelength, we make a single shot that sequentially contains all three waves. These micro pulses are so close together that the skin interprets them sensitively as a single one.
Why can’t permanent hair removal be done with a single laser or photoepilation session?
As we have mentioned, the light from the laser or IPL has to impact the melanin of the follicular bulb to heat it and weaken or destroy it. The hair on our body, like our hair, has a biological cycle that includes a growth phase (anagen), an involution phase (catagen) and a metabolic rest and loss phase (telogen). You can find more information about this cycle here.
Each hair has its own rhythm and not all are in the same phase at the same time. The anagen period is when the hair has the maximum concentration of melanin and, therefore, when it is most sensitive to laser or IPL to obtain a therapeutic response. Those hairs that are in anagen at that time will be removed more efficiently than those that are in catagen or telogen.
Also, depending on the area of the body, there is a higher percentage of hairs that are in the anagen phase. For example, on the scalp there are 85% of hairs that are in anagen at a specific time. However, on the arms and legs, only 20% of the hairs are in the anagen phase. This means that, in one session, the laser will only be most effective on 20% of the hairs on the arms or legs.
If we were to assume that the effectiveness of lasers or pulsed light was 100% -which it is not-, we would see that we would need at least a minimum of 5 sessions to cover all the hairs in the anagen phase.
How often are laser hair removal sessions separated?
To try to catch the maximum number of hairs in the anagen phase, it is necessary to separate the sessions for the duration of the telogen phase from the area to be treated, which is also variable depending on the body area.
How many sessions are needed for laser hair removal?
As we have mentioned, we must at least impact 100% of the hairs in the anagen phase to achieve an appreciable clinical response. If we respect the biological cycle of the hair, at least a minimum of 4-6 sessions are necessary to perceive a noticeable weakening of the hair. With each light impact, the amount of melanin in the bulb decreases, so each session that passes is more complex to remove the hair, since it has less target to absorb light.
In the same way, we can also vary the parameters of the laser. The more aggressive we are with them, the more likely it is that the hair will disappear, but also the more painful the session is and the more likely it is to have adverse effects if the epidermal melanin accidentally absorbs part of the energy emitted by the device. Despite the popularity of laser or pulsed light hair removal, it is not easy to perform it effectively and safely at the same time.
How long do I have to wait to notice the effect of laser hair removal?
It seems that the diode laser is the earliest in terms of effects, with a decrease in hair being noticed about 3-4 months after the first session. However, it is recommended to wait at least half a year to see effectiveness in the treatment.
Why do you have to shave your hair before the session and is it better not to wax it or weaken it with depilatory cream?
If we shave the hair, we are removing all the melanin that remains outside the skin and that would absorb the laser energy in contact with the skin surface, causing burns. On the other hand, with shaving we keep the bulb full of melanin inside the skin, which increases the safety of the procedure.
If we remove the follicular bulb with depilatory cream, wax or other systems that extract the follicular unit by traction, we eliminate the target where the lasers should impact and, therefore, the treatment lacks effectiveness.
Is it possible that laser hair removal will make more hair come out?
Yes. Cases of paradoxical response have been described: the photobiomodulatory effect of lasers or pulsed light can, on rare occasions, cause a proliferative stimulation of the pluripotent cells of the follicular bulb. The solution is none other than to continue with the treatment without the need to change the light system.
Is laser hair removal painful?
Yes. The sudden heating of the hair bulb is annoying for sensitivity. However, with a large refrigerated sapphire head, with the application of cold ultrasound gel and with devices that fire quickly or that join pulses of different wavelengths in the same shot, discomfort is reduced, either due to anesthesia or the need for fewer shots. Laser hair removal can also be performed with anesthetic cream if the patient requires it.
At what age can laser hair removal be started?
Studies indicate that there is no age restriction regarding hair removal with light systems. However, it must be remembered that the hair must be sufficiently developed and have the necessary melanin for the treatment to be effective and as simple as possible. In the same way, l@s patients may pediátric@s have a lower tolerance to the pain associated with the procedure.
The answer, therefore, is not concrete but it can be said that when the patient wishes to wax, there are no contraindications, the dermatólog@ considers that the hair is of sufficient importance for the treatment to be effective and safe, and the parents or guardians authorize the treatment, hair removal with light systems can be carried out.
What does the price of a laser hair removal session depend on?
Basically, the difficulty of the procedure; the lighting device used and the knowledge about hair removal and management of its complications of the center where it is performed.
Those sessions with higher quality lighting systems, which cause less pain, require fewer shots and used by formad@s professionals and with dermatological supervision are more expensive than those that do not meet these quality standards. It is possible that there are also cost differences depending on the location of the center in a town or country.
What is the best laser for hair removal?
Based on reviews, it appears that the combination of Alexandrite laser (755 nm) and Diode laser (810 nm) is superior in effectiveness than either separately or compared to pulsed light.
Can I have laser hair removal or photoepilation if I am taking isotretinoin?
There is no evidence that isotretinoin increases the incidence of adverse effects in any procedure with lighting systems. In fact, this drug gives sensitivity to ultraviolet radiation (200 – 400 nm) but not to visible radiation or other radiation emitted by the lighting systems used in dermatology.
REFERENCES
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· Spring LK, Krakowski AC, Alam M, Bhatia A, Brauer J, Cohen J, Del Rosso JQ, Diaz L, Dover J, Eichenfield LF, Gurtner GC, Hanke CW, Jahnke MN, Kelly KM, Khetarpal S, Kinney MA, Levy ML, Leyden J, Longaker MT, Munavalli GS, Ozog DM, Prather H, Shumaker PR, Tanzi E, Torres A, Velez MW, Waldman AB, Yan AC, Zaenglein AL. Isotretinoin and Timing of Procedural Interventions: A Systematic Review With Consensus Recommendations. JAMA Dermatol. 2017 Aug 1; 153(8):802-809.
· McDonald KA, Shelley AJ, Pierscianowski T, Alavi A. A 2017 update: Challenging the cosmetic procedural delay following oral isotretinoin therapy. J Cosmet Laser Ther. 2019; 21(1):58-60.
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