In terms of hair removal, the professional industry currently uses two light technologies: laser and IPL.
1. A common mechanism of action: light
Lasers and flash lamps generally work on the same principle: the emission of light and the absorption of this light by a target. For hair removal, the target is the pigment contained in the hair (melanin). When the target is exposed to the light emitted, it rises in temperature to reach approximately 70°C; at this temperature, a certain number of biological structures will be altered or destroyed.
This destruction is limited to the elements associated with the hair, eventually preventing regrowth. This is known as “selective photo-thermolysis”. Finally, the following should be noted:
– Light consists of one or severl wavelengths.
– A given wavelength is absorbed by a single target colour (a single pigment colour).
– Hair colour may be very different from one individual to another (ranging from very light blond to very dark brown).
– Each hair colour will therefore specifically absorb a single wavelength of light emitted.
2. Comparison of emission spectra
This is one of the fundamental differences between laser technology and IPL technology.
A. Laser technology
A laser emits “monochromatic” light, (single wavelength).
The value of this wavelength varies according to the laser type (Diode, YAG, Alexandrite, AColorant, etc.)
B. Flash lamp technology
A flash lamp emits “polychromatic” light, (a multitude of wavelengths), also known as a “range of wavelengths”. This “range of wavelengths” is more or less extended/limited according to the filter(s) positioned between the light source (lamp) and the skin.
In comparing the different emission spectra of laser hair removal devices and flash lamps systems, a major difference between these two technologies becomes immediately apparent: the laser has a single wavelength, whereas the flash lamp has a multitude of wavelengths.
3. Specific nature of the target: hair
In terms of hair removal, the only important structure in the hair is its pigment: the melanin.
There are just as many types of pigments (as many colours) as there are different individuals.
Each type of pigment will require a specific type of light (a specific wavelength) to be heated up. When the correct light (wavelength) is captured by the pigment, the melanin starts to heat up.
As the hair itself is saturated with this pigment, it will become heated in its entirety and its temperature will reach approximately 70°C. The hair will then immediately behave like a very hot object inserted into the skin, such as a needle. The heat is therefore transmitted to everything in contact with it, and in particular the structures that nourish the hair. When these nourishing structures are in turn heated, they are altered more or less permanently depending on the amount of heat accumulated.
This more or less permanent alteration will determine the more or less permanent nature of the hair removal. That’s another reason why we call this depilation technique permanent hair reduction and not permanent hair removal.
4. Correspondence of the emission spectra/target:
A – Laser hair removal
Target colour (1) will be heated up by laser 1
Target colour (2) will be heated up by laser 2
Target colour (3) will be heated up by laser 3
Laser (1) will heat up no other target than target 1
Laser (2) will heat up no other target than target 2
Laser (3) will heat up no other target than target 3
B – IPL hair removal
Here we see that all of the targets (hair colours) are covered by all of the wavelengths emitted.
In other words, each target, therefore each hair colour, therefore each individual, finds its corresponding wavelength in the spectrum emitted.
It becomes obvious from the above that:
– Each type of laser will be highly effective on a single type of hair colour, but ineffective on all other colours.
– A flash lamp (IPL), however, will be effective on all of the hair colours encountered Flash lamps therefore seem unquestionably to be perfectly suited to the hair removal application.
Conversely, using a laser to carry out hair removal is truly illogical from a scientific and technical point of view.
5. Hair removal laser in practicee
Despite this observation, the following is still true: a large number of laser hair removal devices are still used for hair removal purposes, most of the time producing satisfactory results for many individuals.
The first laser machines marketed for hair removal were recognised as being highly effective on one type of hair, and not many, or even totally ineffective on all other hair types.
This is perfectly in line with our previous demonstration.
Over the years, laser manufacturers have changed a technical parameter: the power of the light emitted. The power of this emitted light has been increased significantly. As a direct result, the number of target colours “captured” by the more powerful emitted light has increased.
In the end, hair removal lasers have become much more effective over a much wider range of hair colours. In return, however, a new problem has arisen: the increased power has resulted in systematic and unavoidable secondary effects of burns to the skin.
The manufacturers therefore had to incorporate skin cooling at the moment when the light is emitted by the laser.
Depending on the models and manufacturers, these cooling systems vary, ranging from chilled air blowing devices to the application of a cooled lens or cryogenic gel.
To summarise, the effectiveness of lasers in terms of permanent hair removal has been obtained at the cost of a significant increase in their power, resulting in the need to protect the skin by implementing bulky and expensive techniques.
6. Hair removal IPL in practice:
As opposed to lasers, IPL hair removers are perfectly suitable as hair removal devices.
As the correct wavelength corresponding to the colour of the hair treated is always found in the spectrum of light emitted, the power of the source does not need to be increased to obtain clinical effectiveness.
Therefore, there may be a ratio of 1 to 10 or even 1 to 20 between the power of IPL hair removal systems and lasers for hair removal. Lower power means improved safety. Unfortunately, this situation which may appear to be ideal in many cases is not: numerous IPL devices have appeared on the market over the last few years and almost 70% of them have degraded features which have therefore adversely affected their effectiveness and safety.
There are 4 parameters that effectively allow a IPL hair remover to be defined:
– The quality and value of the filtering of the light emitted.
– The “pulse width” or flash time.
– The “fluence” or amount of energy delivered during the flash.
– The “form of the flash” or the regularity of the light energy emitted throughout the duration of the flash.
The clinical effectiveness in terms of long-term hair removal and the risk of undesirable effects (pain) or secondary effects (burns) will depend on the quality of these 4 parameters.
The very large diversity of hair colours encountered in the practice of hair removal makes laser technology implicitly unsuitable in terms of effectiveness and safety.
Conversely, the more recent flash lamp technology turns out to be perfectly suitable for hair removal, combining greater effectiveness and much higher safety.
This observation must however be weighed up: the quality of marketed equipment often varies significantly as far as laser and IPL hair removal devices are concerned: most hair removal laser machines are of a good price and good quality. On the other hand, at least 70% of the flash lamps currently offered for hair removal are of poor, or even very poor quality.
The poor quality of many professional IPL machines unfortunately discredits this technology, even though flash lamps are technically more suitable for hair removal treatments.