A Reminder of the Basic Principle

In laser hair removal, the target—or chromophore—is melanin. To achieve destruction through selective photothermolysis, the chromophore must absorb more laser energy—or fluence—than the rest of the skin. Therefore, a laser is used that emits at a wavelength within the absorption spectrum of melanin.

For fair skin, very specific wavelengths related to melanin can be used, since the contrast is pronounced and the epidermis therefore absorbs very little energy from the laser. For dark or very dark skin, a wavelength that is less specific to melanin is used, and the treatment relies on the hair’s ability to absorb more energy than the skin, since the hair contains more melanin in this skin type.

Wavelengths Used in Laser Hair Removal

The main wavelengths absorbed by melanin are as follows.

Alexandrite lasers (755 nm) are offered by Candela (GentleLase, GentleMax Pro, which combine alexandrite and Nd:YAG), Cynosure (Apogee, Elite+, Elite iQ), DEKA (Motus AX), Lutronic (Clarity II), Quanta System (Thunder MT), and Cutera (Excel HR).

Diode lasers (approximately 800 to 810 nm), the most common in clinical practice, include Lumenis (LightSheer Duet, Desire, and Quattro), Alma (Soprano ICE, Titanium, and Platinum), Asclepion (MeDioStar), Cynosure (Vectus), Venus Concept (Venus Velocity), and the diode modules of Sciton’s Joule platform.

Nd:YAG lasers (1,064 nm), which are less selective for melanin and therefore suitable for dark or black skin, include Candela (GentleYAG), Cutera (CoolGlide), DEKA (Motus AY), Lutronic (Clarity II), and Fotona (Dynamis).

In summary, the art of laser hair removal consultations lies in the physician’s ability to assess the contrast between the hair—its color, thickness, and density—and the skin, according to the Fitzpatrick classification.

Once a clinical diagnosis has been made, the laser must be configured.

The Three Key Factors You Need to Know

Fluence

This refers to the energy delivered by the laser to a surface; it is expressed in J/cm². This concept of energy per unit area is very important. In fact, a fluence of 16 J/cm² with a 12-mm spot on an alexandrite laser delivers approximately 14 J per pulse, whereas a fluence of 16 J/cm² with a 20-mm spot delivers 50 J—nearly four times as much energy. This is why energy levels cannot be set very high with very large spots.

At a constant maximum energy level, a smaller spot size allows for a higher fluence. At the same fluence, a larger spot size requires more total energy. Therefore, it is sometimes necessary to reduce the spot size to achieve higher fluences and maintain efficiency, at the expense of processing speed.

Spot size

Diameter, small head, large head: there are many options for covering a larger area. However, as explained in the section on fluence, the treatment area affects the total energy delivered, with a limit determined by the machine’s maximum energy capacity.

If the spot size increases, the beam’s penetration depth increases. It’s useful to know this, but it’s not particularly helpful in practice. The belief that deeper is more effective has no physical basis: lasers with small spots are calibrated to reach the bulbs.

Pulse duration

This refers to the duration of energy delivery with each shot. Again, this concept is important. The key point to remember is that the destruction of a target by a laser is related to its thermal relaxation time, or TRT.

In a nutshell, TRT is the time it takes for a target to dissipate 50% of the heat it has accumulated. In this article, we’re discussing the TRT of hair. The thicker the hair, the longer its TRT, and the more we can increase the pulse duration in milliseconds. The finer the hair, the more you need to reduce the pulse duration to be effective. But be careful: you’re then getting closer to the TRT of skin melanin, and if the skin doesn’t have enough time to dissipate the heat, a burn will occur. At 2 or 3 ms, there’s no margin for error.

To put it simply, a shorter pulse duration increases the energy output, which rises by a factor of 10 between 20 ms and 2 ms. So, be careful with the milliseconds.

How to Do It in Practice

First and foremost, we learn about the theory of medical lasers. That’s what the Laser SAMBA module is for.

You’ll encounter two types of lasers: those with a multiple-choice screen and a clinical questionnaire, and those without. If you have a questionnaire, you’ll enter the hair type, color, density, and length, as well as your skin type. The machine will then make a recommendation. After that, it’s up to you to fine-tune the settings if necessary.

If you don’t have a multiple-choice screen, you’ll be provided with a parameter chart from the manufacturer. It’s up to you to transcribe the parameters you find based on your clinical analysis.

Tips for Beginners

• Perform a test before beginning treatment. Tests are always performed on the areas most exposed to sunlight in order to assess the area at highest risk.
• On the day of the treatment, test the product on your legs and treat your bikini line and underarms in the meantime. Your legs may have tanned a bit, so it’s best to be very careful, since burns on the legs are difficult to manage: they’re visible and cover a large area. In short, you need to be careful.
• Set the energy level 2 joules lower than the “OK” test: this leaves a margin, and during the first few sessions—when the hair is thick—you’ll be just as effective.
• At the end of the session, do a test with 2 to 4 joules more to establish a baseline for the next session, so you can increase the fluence and then reduce the milliseconds if the hairs become too fine.
• Don’t set thousands of different parameters for your patients: you won’t be able to establish a baseline, you won’t be able to make comparisons, and you won’t make progress. That’s the surest way to run into big trouble.
• Don’t vary two parameters at the same time from one workout to the next: you’ll never know which one made the workout effective or helped you burn calories.

When the burn is still there

Despite all these precautions, hair removal lasers can still cause injuries of varying severity.

The Different Degrees of Burns

• First-degree burn: simple erythema, or sunburn, and a scab—a brown spot on the skin’s surface—which sometimes appears following treatment. Fortunately, this is by far the most common type of burn seen in laser hair removal treatments.
• Superficial second-degree burn: blister.
• Deep second-degree burn: the dermis is affected, with a risk of scarring.
• Third-degree burn: complete destruction of the skin; a skin graft may be necessary.

Coverage

First and foremost, you need to cool the area: cold water, a cold cloth. It should be cool, not ice-cold, otherwise it will make the injury worse. It depends on the area, but you need to cool it immediately.

Superficial first-degree burns heal on their own; you just need to avoid friction and scratching to prevent secondary infection.

Generally, they appear as a small brown spot that disappears after 7 to 10 days, leaving lighter-colored skin in its place—especially if the skin was previously tanned: this is hypopigmentation.

It will last a few months, then gradually fade, both as the depigmented areas regain their color and as the tanned area around them shrinks. It’s important to reassure the patient: these first-degree burns do not leave any scarring; the skin will eventually regain its pigment, although this may take time, sometimes depending on the patient’s skin type.

More rarely, superficial second-degree burns may occur, characterized by a phlycten, or a water blister. In such cases, they must be treated. Once again, treatment begins with immediate cooling; after that, it follows the standard protocol for burns: clean the area with mild soap, keep it clean, and, if necessary, apply a non-adherent dressing until re-epithelialization occurs.

In any case, avoid UV exposure by using SPF 50+ sunscreen until the skin has fully healed.

As always, the most important thing is to maintain close contact with the patient: providing reassurance and follow-up care.