There are things to consider, principally:
-- Wavelenghts (nm)
The laser wavelength for deep, thick & dark hair roots should be 1064nm (Nd:YAG); but it won't be effective for shallower hair roots.
The laser with wavelength of 755 nm (Alexandrite) & 800-900 nm (Diode) work effectively with shallower, thinner & lighter hair roots.
Many IPLs & Lasers with other wavelengths do not work effectively to retard hair growth. So before you pay, ask the therapist what wavelength they use to remove your hairs? Because if your hairs root deeply, energy form lasers & IPLs with shorter wavelengths won't reach your hair roots; vice versa shallower hair roots won't respond well to lasers with longer wavelengths
-- Skin colours
Nd:YAG is suitable for all skin types, but Alexandrite & Diode are safe to be used for Fitzpatrick Skin Type 1, 2 & 3 only.
Very dark-skinned individuals need to have a laser with a longer wavelength. The longer wavelength is needed so as not to have the laser energy preferentially absorbed by the top layer of skin as would occur with the shorter wavelength laser. The longer wavelength penetrates deeper and will target the deeper dark pigment decreasing the risk of blisters or burns on the surface.
-- Natural Hair Colours
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-- Density & diameter your dark hair roots
The treatments are most effective on dense, thick, coarse & dark hair roots because they have a lot of pigment and can absorb a lot of heat. Sparse, fine hairs cannot absorb much heat. Thus, LHR lose efficacy on very thin or vellus hairs.
-- Pulse Duration
Laser devices operate as continuous wave or pulsed systems (e.g. single or repetitive‑pulsed lasers). Examples of multi-pulsed (in other word, repetitive-pulsed) laser devices are Short Pulsed, Long Pulsed and Q-switched for different treatment purposes. But long-pulsed lasers in 755, 800-900 & 1064 nm have proved to be effective to reduce hairs permanently.
Q-switched & other short-pulsed lasers which emit much shorter pulses won't do anything to your hairs except bleaching hair colors. Both the amount, density & size of your hairs will remain exactly the same. Remember! Once hair roots get bleached, IPL & Laser won't work on lighter hairs 😭.
-- Fluence (J/cm^2), Spot Size (mm) & Repetition Rate (Hz) to be applied are according to different recommendations among different brands.
In general, the smaller the spot size the higher the fluence.
Settings can be increased or decreased depending on the previous results and clients' feelings during different sessions.
Rule of thump: Look for perifollicular edema which should appear few minutes after firing
-- Phase of the hair growth cycle
Laser & IPL can only target the anagen.
At any given time, not all hairs are in the anagen phase.Therefore, multiple treatments are required to achieve the optimal appearance.
Timing between treatments is very important for optimal results with laser hair removal. It is important to pay for treatments one by one vs paying for packages of laser services up front. Different areas of the body have different hair growth cycles. In order to catch the most hair in the active cycle (or anagen phase) during your laser hair removal sessions, treatments should be scheduled according to the hair growth cycles.
In general, the best way to approach this is to use the regrowth of hair in the treated area as your guide... in other words, when a significant percentage of the hair starts growing back, return for the next treatment.
It could be as short as 4-6 weeks on the face, and as long as 8-12 weeks (or longer) for the legs. Bikini, chest, back, underarms, stomach etc. should be scheduled every 6-8 weeks, as for examples. These are different among different individuals.
Typically 6-8 sessions for each certain body area are recommended to catch each cycle of hair growth, although some people may be satisfied with their results sooner. Some may require more sessions. Following these guidelines should result in the greatest reduction of hair.
However, once desired results are achieved, many people come back annually for 1-2 treatment maintenance sessions. While in the maintenance phase, the ideal time to get a touch-up session is when you notice there are times when hair growth seems to be more aggressive. This is, as hair in the active growth phase is most effectively targeted.
Another recommended alternative would be to START WITH LASER treatment. Multiple laser sessions will be required. Once desired results are achieved by laser, then you may choose to FINISH WITH ELECTROLYSIS. This is the fastest way to achieve the optimal appearance (be it total removal or just thinning of the hair).