Page 44 - Chapter 3 - Fundamentals of Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 1st Edition
applying a layer, typically 2-5 mm thickness, of cool (temperature around +5oC) water-based gel on the skin prior to treatment.
Unfortunately, this procedure is still one of the most frequently used. So, what is the problem with gel-based skin cooling? It is normally better than no cooling at all, but the two main problems are that gel cooling is very inconsistent in terms of cooling depth and the skin area distribution is typically much larger than the spot size.
The lack of understanding of the importance of consistent and depth- controlled skin cooling in light-based skin treatments is probably one of the main reasons for the high frequency of unwanted side-effects in SPT treatments.
The main problem is lack of control of the skin cooling time. Typically, a pretty large skin area of around 25-100 cm2 (5x5 cm to 10x10 cm) is covered with gel. Typically, it takes several seconds before the even the first light pulse is applied and it may take minutes to complete the area with cooling gel.
The skin will immediately start warm up the gel so the gel will become warmer and warmer over the procedure time to complete gel covered area. Thus, at the end of the treatment the cooling effect might be negligible if the thickness the gel layer is thin. The lesson from this example is that skin cooling not only should be depth controlled but as confined to the spot area of the light pulse. No area outside of the light spot should not be cooled down prior to the next pulse as this would cause inconsistent skin cooling.
There are now a number of different skin cooling principles methods available on lasers/IPL devices. The methods are based on cool gel, ice, cryo gas spray burst, forced cooled air and contact cooling with heat sink. All these methods have pros and cons.
The cooling methods shown in below image are poor and can neither control the cooling depth nor confinement to the spot size.
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