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Selective photothermolysis, or how it works
The mechanism rests on selective photothermolysis. The energy of the laser light is absorbed selectively by melanin, present in the skin or in the hair, and turns into heat. That heat destroys the target structure: pigment deposited in the skin or the hair follicle.
The word „selective” is the key one here. Tissues that do not absorb this wavelength are left largely untouched. This sets this laser apart from ablative devices such as the CO2 laser, whose chromophore is water, present in every tissue.
Why 755 nm and melanin are a pair
The 755 nm range is marked by high absorption by melanin, higher than the wavelengths used in other hair removal lasers. This has two consequences that are worth understanding together rather than separately.
What it gives
Strong absorption means that even a small amount of pigment is enough for the energy to be taken up. That is why this range is sometimes chosen for fine and lighter hair, difficult for lasers with a longer wavelength.
What it limits
Melanin in the epidermis absorbs the same wavelength as the target pigment. With a darker phototype and with a fresh tan the epidermis competes for the energy, which is why more careful settings or a different laser are then chosen.
This is why the assessment with this laser begins with judging the phototype on the Fitzpatrick scale and with the question about the last exposure to the sun, rather than with the choice of treatment area.
The absorption window, or what 755 nm is taken up by
The skin contains three main chromophores, that is substances that absorb light: melanin, haemoglobin and water. Each of them absorbs differently depending on the wavelength, and the effectiveness of the treatment depends on whether the chosen wavelength hits the target and passes the others by. In hair removal the target is the melanin of the hair follicle.
Below, how this looks for the 755 nm range. The length of the bar corresponds to the strength of absorption, and the light background shows the full scale.
755 nm
the range of this laser
Melanin
Haemoglobin
Water
From this follows the role of this range in hair removal. Melanin absorbs clearly here, haemoglobin weakly, and water practically not at all. The beam therefore reaches the pigment of the follicle instead of scattering energy on vessels and in tissue. That is the sense of the word „selective” in the name of the mechanism.
A schematic comparison, based on the absorption curves of skin chromophores.
Adjusting settings and the spot diameter
Adjusting settings
Being able to change the working settings makes it possible to adapt the treatment to different skin types and different indications, rather than putting everyone through the same protocol.
Spot diameter
A larger diameter of the light spot covers a bigger piece of skin in a single pulse, which shortens the time needed for extensive areas such as the legs or back.
Careful escalation
The settings are increased gradually, watching how the skin responds. With a laser with such high absorption by melanin this is the basic safeguard against an adverse reaction.
We do not give the trade names of the devices, because we do not build an advantage on the brand of equipment, and the regulations limit advertising of medical devices addressed to the public. What matters is the settings it is possible to work with and how carefully they are escalated.
Indications
Both wavelengths in one pulse
The platform we use for this wavelength can deliver 755 nm and 1064 nm to the same place, simultaneously or one after the other, with an adjustable interval. A single pulse then covers a wider range of hair thickness and depth than either wavelength can on its own. We describe this on the page about the Nd:YAG laser.
When 755 nm is too risky
High absorption by melanin, that is the greatest advantage of this wavelength, becomes its limitation with darker skin phototypes: the melanin of the epidermis then competes with the melanin of the follicle for the energy. In such situations we reach for a longer wavelength, absorbed less by the epidermis. We describe it on the page about the Nd:YAG 1064 nm laser.
For hair removal we describe how it goes, the number of treatments and the recommendations on the page about laser hair removal, and for pigmented lesions the choice of technology on the page about laser pigmentation removal. This page describes the device itself and its properties.
The limits of the method and when to be more careful
Grey and very fair hair does not contain enough melanin to absorb the energy. Laser hair removal will not cover it, whatever the number of treatments.
A darker phototype requires more careful settings, and sometimes a different laser, because the melanin of the epidermis competes with the target pigment.
A fresh tan rules out the treatment for as long as it lasts. That is not a matter of preference but of safety.
We do not give a number of treatments or a degree of improvement before the assessment. They depend on the area, the thickness and colour of the hair and on the growth phase the follicles are in.
The treatment on video
The recording will show the handpiece at work, the way the skin is cooled and what the area looks like immediately after a series of pulses. It answers the two most common concerns: whether the treatment hurts and how the skin reacts straight afterwards.
After the treatment
Temporary redness is possible, as is perifollicular swelling, which in hair removal can be a sign that the melanin of the follicle absorbed the energy.
No sunbathing or sunbeds before and after the treatment, for the period given by the person carrying it out.
Daily sun protection on the treated area throughout the whole course.
Between hair removal treatments shaving is advised, without pulling the hair out, which disturbs the effectiveness of the next session.
Contraindications
Tell us about the medicines you take, because some of them increase the skin's sensitivity to light, and about any tendency to post-treatment pigmentation.
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Responsible for the content
NL Clinic, Katowice
How the content is created
Last updated
14 August 2026
This material is informational in nature and does not replace a consultation or qualification.
The questions we are asked most often
What makes the 755 nm wavelength stand out?
It is a range with high absorption by melanin, higher than the wavelengths used in other hair removal lasers. The energy is strongly absorbed by the pigment in the hair shaft and follicle, which translates into effectiveness with fine and lighter hair, difficult for lasers with a longer wavelength.
What is selective photothermolysis?
The energy of the laser light is absorbed selectively by melanin in the skin or in the hair, which leads to it heating up and the target structure being destroyed. Tissues that do not absorb this wavelength are left largely untouched. The choice of settings decides whether the heat stays in the target or passes to the surroundings.
Is this laser suitable for every phototype and every hair colour?
Adjusting the settings makes it possible to adapt the treatment to different skin types, but the assessment is carried out individually. Strong absorption by melanin means that with a darker phototype and with a fresh tan the risk of adverse reactions rises, which is why more careful settings or a different laser are then chosen. Grey and very fair hair does not contain enough pigment to absorb the energy, so it does not respond to laser hair removal.
Why does a larger spot make the treatment faster?
A larger diameter of the light spot covers a bigger piece of skin in a single pulse, so covering a large area needs fewer pulses. This matters on the legs, back and other extensive areas, where it shortens the treatment.
What besides hair removal is this laser used for?
For work on pigmented lesions, because the same mechanism, that is energy being absorbed by melanin, also works on pigment deposited in the skin. We describe the choice of technology for a particular pigmented lesion on the page about laser pigmentation removal.
Can the treatment be done in summer?
A fresh tan is a contraindication for as long as it lasts, because the melanin in the epidermis then competes with the target pigment for absorbing the energy. The treatment is possible outside the tanning period, with sun protection kept up before and after the session. The date is set by the person carrying out the treatment.
The content is for information. It does not replace a consultation, an examination or an individual assessment.