Page 17 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Hair Removal using Light Energy – in a nutshell
This is a basic introduction into how light energy can be utilised to destroy hair follicles.
Many people have unwanted hair. For years, hair has been removed using tweezing, waxing, shaving and electrolysis. Since the 1990s, lasers and IPLs have been used, quite successfully.
The basic principles behind light-based treatments are the following:
1. Hair contains a pigment called melanin – this can be eumelanin (black-brown) and/or pheomelanin (red-yellow). Dark hairs have a higher concentration of this pigment than lighter hairs.
2. We can target this pigment using light and a process called ‘absorption’. To maximise the absorption we must choose a suitable wavelength of light – that is, the colour of light. With suitable wavelengths we know we can ‘force’ the melanin to absorb more light than the surrounding tissues, leading to preferential heating. (We are all familiar with this method of heating – when we walk around on a sunny day, the tissue water in our dermis absorbs some of the infrared light energy from the sun. This is converted on to heat, which we can clearly feel.)
3. There are a number of systems which can be use to target the melanin in hair (see Figure 1 - Hair removal systems and their place in the spectrum) including diodes, long-pulsed Nd:YAG and Nd:YAG alexandrite lasers. In addition, IPL systems can also generate good results with hair removal.
4. When the pigment absorbs some of the light falling onto it, the light energy is converted in to heat energy, raising the temperature of that melanin. This is the whole purpose of light-based treatments – to heat up the melanin.
5. However, the epidermal melanin will also heat up since it is in a layer above the hair follicles. If the skin is light coloured, then then it will not get too hot. But, as the skin becomes darker, the induce temperature will increase – for the same incident light energy.
6. For these reasons, ideally, we want to treat dark hairs in a pale skin – this contrast between hair and skin colour ensures that more of the light energy is absorbed in the hair melanin, than in the epidermis. It is the relatively high concentration of melanin in the hair that causes it to be preferentially heated.
7. As the contrast between hair and skin colour decreases, the difference in temperatures between them also decreases. If the skin is too dark (i.e. too much melanin) then the epidermis is at a high risk of being damaged by this process.
________________________________________________________________________ 17 Chapter 3 Laser/IPL Hair Removal
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