Page 236 - Mike Murphy's Blog Posts

E16 - Do you need gel for photothermal treatments?
Water-based gel is routinely used when applying lasers and IPLs on skin conditions like vascular lesions, benign pigmented lesions and hair removal. However, some manufacturers and suppliers suggest that gel is not required. I’m not really sure why!
So, what happens if you use, or don't use, gel?
As far as I am concerned there are two reasons to use gel:
1. to help more light enter the skin through index-matching and, 2. to help thermal energy escape from the skin more efficiently.
Light coupling:
When light approaches the skin surface it encounters a change in refractive index and reflection (known as Fresnel reflections). A small amount of gel will help to reduce the change in refractive index between the air and the skin, thereby increasing the amount of light energy entering the skin.
Thermal conduction:
The dermis is full of water (around 70% of the dermis is water). Water conducts heat four times faster than air. So when heat energy within the dermis reaches the skin surface the transfer of heat slows right down. This 'traps' that heat energy in the skin leading to unwanted elevated temperatures. By applying a water-based gel on the surface the heat energy can easily leave the skin and warm up the gel.
I took the following photograph after i noticed the effect of an IPL pulse on a wooden spatula. The IPL was set at 36 J/cm2 with a pulse duration of 30 milliseconds. The left side shows the burning effect of this energy on the surface of the wooden spatula when no gel had been applied. The right side of the photo shows the same energy on the same spatula but where a little cooling gel had been applied.
Mike’s Blog Posts 236