Page 62 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Many of these nerve endings are located just below the epidermal-dermal junction i.e. just below the skin surface (Figure 25).
Figure 25 – The nerve sensors in human skin
This layer is very thin typically around 60 to 100 microns (that is 0.06 to 0.1 mm), so it can become quite hot but will lose its heat energy rapidly. Unfortunately, the pain receptor nerve endings (nociceptors) are located in the epidermis and upper dermis, just below the basal layer (see image above). As the heat energy conducts into the upper dermis the temperature and pain receptors will be stimulated. NASA research has found that our temperature sensors will indicate heat up to around 45°C. Above that, they ‘switch off’ and the pain receptors kick in. This is to inform the brain that the temperature is approaching levels which could damage cells and tissue.
This is the main reason for pain during laser/IPL treatments. It is a direct consequence of the locality of the nerve endings in and just below the epidermal layer. The speed at which the heat energy conducts from the epidermis depends on its thickness. Darker skin will have more melanin in it, and so will conduct (lose heat) more slowly than lighter skin. Hence, darker- skinned individuals will likely feel more pain than a lighter-skinned person, for exactly the same light energy input.
Pre-Cooling
For this reason, the concept of ‘pre-cooling’ is absolutely critical in reducing the pain sensations felt during treatments. By reducing the temperature of the epidermal layer before
________________________________________________________________________ 62 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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With photothermal treatments, the heat sensors can be triggered by heat flowing from the epidermal melanin and from heated tissues in the dermis. These nerves are triggered at a temperature of 45°C, which is only 10°C higher than the normal, dermal temperature! So, it doesn’t take much fluence to induce a painful sensation in the skin.
The basal layer between the epidermis and dermis contains many melanocytes and melanin granules. Over time, these melanin granules migrate towards the skin surface. Darker skin contains many more melanin granules throughout the epidermal layer compared with lighter- coloured skin. As a consequence, the epidermis can absorb a significant amount of light energy in the visible part of the spectrum.