Page 139 - Chapter 3 - Laser/IPL Hair Removal

Chapter 3 – Fundamentals of Laser/IPL Hair Removal 2nd Edition
Figure 80 - Temperature drop in the skin over 5 minutes, with subsequent reheating
After two minutes, the temperature keeps falling, but quite slowly. Most of the difference occurs in the first two minutes, which is why we recommend pre-cooling the skin for this duration before applying light energy.
At five minutes, the cooling effect is removed, and we see the temperatures all rising again. This is primarily due to the heat supplied by fresh blood and the ambient air temperature. However, it is interesting to note that the rise in temperature is relatively slow, compared with the cooling rate.
Ice cooling is, by far, the most efficient way to cool the skin. Air and cryogen cooling are not as efficient and definitely do not achieve the depth of cooling that ice packs do (see later in this section).
“Over-cooling” the treatment area is virtually impossible!!
For years we have been teaching people to pre-cool the skin surface before firing laser or IPL energy into the skin when treating hair. And we’ve always suggested pre-cooling for between 2 and 5 seconds. Our thinking was that we should not “over-cool” the skin because that might lower the temperature of the hair follicle too much.
It turns out we were wrong!!
The whole reason for cooling the skin is to lower the temperature of the thermal pain nerves, located just below the epidermal/dermal junction. By doing so, they will not trigger until their temperatures is raised above 45oC – this will require more fluence if they are pre-cooled by 10 or 15oC.
________________________________________________________________________ 139 Chapter 3, Ed. 2.0 Laser/IPL Hair Removal
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