How Laser/IPL Treatment Works
Before we can fully understand how laser hair removal works we need to look at the process of hair growth. On the surface of the skin all hair looks the same but the condition of the hair follicle is vitally important to the success of laser hair removal. The growth and shedding cycle of the hair follicle is divided into three phases:
The effects of Ruby Laser light on hair growth was first observed by Professor Marc Clement Dean of Faculty at The Swansea Institute, Wales whilst conducting a scientific experiment. This discovery was followed by substantial theoretical and experimental studies leading to the prediction of laser parameters that should achieve depilation.
Starting with a basic understanding of the laser tissue interaction, computer models were constructed to simulate effects on hair and surrounding skin when illuminated with intense pulse laser light. These models allowed the prediction of the laser parameters necessary to achieve depilation whilst minimising the risk of unwanted side effects. The ultimate goal being a fast and safe procedure, which could be carried out on the vast majority of the population.
On completion of the theoretical study, an ethically approved trial was carried out to determine if the computer prediction matched the clinical reality. Laser depilation is based on the technique know as selective photothermolysis. This is based upon the principle of using laser energy to selectively destroy a target beneath the surface of the skin whilst leaving the surrounding healthy tissue intact. The premise is therefore to irradiate the skin surface with a suitable laser source, which only deposits its energy in the target, the light passing harmlessly through the other tissue components.
For selective photothermolysis to be achieved, the following criteria has to be taken into consideration;
The target must contain a chromophore, which can selectively absorb that particular wavelength, in some cases the primary target does not contain a suitable chromophore but is in sufficient close proximity to such a substance to allow selective destruction via a secondary mechanism.
- The surrounding healthy tissues must have a minimum amount of the chromophore allowing light to be transmitted freely through it.
- The absorption of laser energy in healthy tissue does not produce any irreversible or long-term damage.
- The laser light incident on the target vessels is sufficient, in both intensity and duration, to induce the desired clinical effect; often this is the heating of the target above a certain threshold and holding it there for a certain minimum period.
An analysis of these requirements leads to a theoretical model, which in turn can lead to a set of laser parameters for optimum treatment efficiency.
The key laser parameters that are applicable to select photothermolysis are;
- Pulse duration
- Energy density
By looking at the physical structure of the skin and hair follicle, the nearest suitable chromophores for absorption of laser energy are the melanin’s in the hair shaft. The laser light has to pass through the epidermis and the upper dermis before interacting with the hair shaft. Since the light has to pass through various skin layers prior to interacting with the hair shaft, other chromophores within the skin influence the choice of wavelength.
Wavelengths within the range of 640-760 n.m. ensure minimum interaction with the oxyhaemaglobin thereby limiting any damage to the capillary network and penetrate to a suitable depth in order to produce the desired effect.
The intention of this theory of depilation is to induce thermal necrosis of the follicular tissue. Heat is generated in the cells via a secondary effect, which involves the absorption of incident light energy in the hair shaft. Diffusion of this thermal energy outwards to the surrounding tissues eventually reaches the follicle, which is in close proximity to the hair shaft. Pulse duration is limited to 1m.sec in order to limit cell necrosis to the follicle and not to the surrounding tissue.
Factors which affect the performance of individual lasers
Wavelength – individual wavelengths have different effects on the skin tissue and on how the laser light is absorbed. The optimum wavelength for hair removal would be highly absorbed in the concentration of melanin in the hair shaft and transmitted harmlessly through the surrounding tissue.
Pulse Duration – this is the length of time the laser light is in contact with the skin. The heat must be maintained for long enough to destroy the hair growth mechanism, but not too long as to burn the skin. The ideal pulse duration required to generate the correct amount of heat in and around the hair follicle is approx. 1 millisecond. If the pulse duration is too short not enough heat will be generated to destroy the follicle. If the pulse duration is too long heat may dissipate into the surrounding skin increasing the risk of burns.
Clearly the greater the energy density, the greater the thermal energy deposited in the hair shaft and subsequently the follicular tissue. The challenge, remembering the existence of some melanin, the target chromophore in the basal layer and epidermis, is to deposit sufficient energy in the hair shaft without damaging the surface of the skin. The required energy density to induce cell necrosis, whilst maintaining the integrity is in the order of 10-25 J/sq.cm.
Chromos 694 Ruby Laser Wavelength – 694nm
Pulse duration – 1m.sec
Energy density 10-25 J/cm²
Energist Ultra VPL Wavelength – 530nm – 950nm
Pulse duration – 3ms 5ms 7ms
Energy density – up to 51 J/cm²
The use of Ruby Laser and Ultra VPL for long-term removal of unwanted hair growth is becoming the treatment of choice in the field. These techniques have been shown to offer long-term depilation in a range of skin types without scarring.