Page 121 - Chapter 3 - An Introduction to Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
Figure 58 – Thermal pain receptors are located just below the basal layer of the epidermis. These are triggered by the hot melanin following laser/IPL treatment. Pain is triggered at 45oC, so cooling the nerve endings reduces the pain sensation felt by the client/patient.
Cooling the nerves endings has the effect of ‘pushing’ them down from the skin surface!
The typical dermal temperature is around 37oC, while the pain receptors trigger at 45oC. This means that there is only an 8oC difference between the normal dermal temperature and the temperature at which the client/patient will feel thermal pain. By applying a little cooling at the skin surface, the pain receptors’ temperature may drop by 10oC – creating an 18oC ‘window’. More cooling may reduce the receptors’ temperature to 17oC, meaning that there is now a 28oC window before pain is triggered.
Apart from feeling less discomfort during the treatment, this allows the laser/IPL operator to use higher fluences, which ensure a higher probability of success.
The temperatures achieved in the epidermis can only be calculated by numerically solving the heat equation since it involves simultaneous heating and cooling, which we did in our model. The important conclusion here is that sufficient skin surface cooling must be applied to mitigate for the temperature increase in the epidermis to minimise the pain sensations and reduce the likelihood of epidermal and upper dermal damage.
The importance of surface cooling cannot be overstated. Without it, patients will probably be ‘burned’ by the laser/IPL outputs. To ensure a good level of clinical success requires the proper incident energy densities (fluences) coupled with sufficient surface cooling.
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