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A29 - Laser-skin treatments and skin cooling – should we do this?
There appears to be some confusion about the use of skin surface cooling and laser treatments.
Why should we use skin-cooling at all? Let’s go back to basics...
When we use lasers to remove hair, blood vessels, benign pigmentation, acne and tattoos we want to induce some sort of reaction in those targets using heat. To generate that heat in those targets, we use light energy – lasers or IPLs.
When the targets absorb some of that light energy, it converts into heat energy, which raises the temperature of the target.
So, the light is merely a way to transfer energy into the targets and generate heat. We use particular wavelengths of light to target particular tissues or tattoo inks. By matching the wavelength with the target, we can maximise the amount of light energy absorbed, and, hence, the local temperature rise.
However, the problem is that most of these targets are found in the dermis. So, the light needs to traverse through the epidermis, and the melanin-rich basal layer, to get there.
Absorption and temperatures
Most of the wavelengths we use on skin treatments (typically between 400 and 1200nm) will also be absorbed by the melanin in the basal layer. Lower wavelengths (towards the blue and green end of the spectrum) are more strongly absorbed than red wavelengths.
This will result in a temperature rise in the basal layer. This is inevitable and unavoidable! If the temperature becomes too high, then the tissue water around the melanosomes (granules of melanin) will boil, resulting in the formation of steam bubbles and frosting. This can cause physical damage to the basal layer which can be seen as blistering.
If these high temperatures exist for too long, the epidermis, and upper dermis, can be severely damaged.
In addition, the thermal pain nerves live just below the epidermis, in the top layer of the dermis (see my video above). If the basal layer becomes hot, the heat will conduct down to the thermal nerves very rapidly. Once they reach a temperature of 45C, they will indicate pain to the brain. The normal temperature of the dermis is around 37C, so it only requires an increase of 8C to trigger the pain nerves!
This does not need much light energy (from any source) to achieve!!!
Mike’s Blog Posts 96