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. (see video below)
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!!!
Applying skin cooling
The purpose of surface skin cooling is to prevent, or minimise, these unwanted effects.
By applying a good level of skin cooling, the epidermis and upper dermis temperatures will drop. This includes the temperature of the pain nerves too. The longer the cooling is applied, the colder the skin becomes!
If the cooling induces a temperature drop of, say, 20C, in the pain nerves, then any heat energy would need to raise their temperature by 28C to reach painful levels, instead of just 8C.
Applying ice cooling to the skin surface for a few minutes can achieve a 20C drop in these nerves. This can reduce the pain sensations significantly! I know from personal experience. I’ve fired 40 J/cm2 from an IPL to my arm skin after 4 minutes of ice cooling – the pain level was about 2/10.
My arm 8 months after a 35 J/cm2 pulse – no pre-cooling
I later fired 35 J/cm2 to my arm with no pre-cooling – the pain level was closer to 9/10. This also resulted in a large blister subsequently. After a few months, this area was still hypopigmented, whereas the other area (40 J/cm2) was perfectly fine.
My arm 8 months after a 40 J/cm2 pulse
– 4 minutes of pre-cooling
I’ve done the same with diode lasers too, with very similar results. I suggest you try this for yourself to feel the effectiveness of good skin cooling.
Incidentally, skin cooling can also be achieved using air coolers, such as the Zimmer device. While this is good to a certain level, it’s not as efficient as ice cooling. This is simply because ice/water cooling is around 20 times more effective due to heat conduction (compared with air cooling). So, using a Zimmer is good, but using it in conjunction with ice cooling is much better.
The benefits of skin cooling
So, apart from pain control, what are the benefits of skin cooling?
Well, by minimising the temperatures in the basal layer, you also reduce the risk of blistering and pigmentation generation. In some people, new pigmentation can be generated following laser treatments. Cooling will reduce the risk of this too.
More importantly, by reducing the skin temperature, you can apply higher fluences without causing excess pain or tissue damage. As I said above, with a few minutes ice cooling I was able to tolerate 40 J/cm2 easily on my skin. I seriously doubt many people could tolerate that level of fluence without cooling!
Many devices use cold tips which also help to cool the skin. While this is true, many of these tips will warm up during treatments. That’s because the device’s internal cooling system is not powerful enough to keep the lamps or diodes cool, whilst also keeping the skin cold.
My advice is to regularly check the temperature of your device’s tip on your own skin during treatments. If it feels ‘warm’, stop the treatment until it cools down. This may take a minute or two (depending on your room’s air temperature!!)
Post-cooling
I have calculated that many laser/IPL treatments ‘waste’ around 90% of the light energy! Less than 10% of the energy we fire at the skin actually does the job were trying to do. This is due to loss of light energy due to back-scattering (out of the skin altogether), absorption by other tissue components and transmission through the dermis.
As a direct consequence, most of the light energy that remains in the skin will be attempting to heat up other tissues, such as the collagen. We must deal with this excess heat energy quickly, before any damage is done.
The most efficient way is to apply ice packs immediately after an area has been treated. This will draw out the excess heat quickly and significantly reduce the risk of unwanted skin damage.
I recommend cooling the skin for at least five minutes after each treatment to ensure proper cooling.
Summary
When we treat hair, vessels or pigmentation we are deliberately inducing a temperature rise in the skin. But this must be a highly controlled temperature rise. It must be ‘balanced’ with sufficient cooling to prevent unwanted thermal damage.
If you increase the fluence applied to the skin, you must also increase the skin surface cooling commensurately.
If you don’t cool sufficiently, you run a much greater risk of damaging tissues such as the epidermis and/or collagen. You are also limited to using lower fluences to reduce pain.
And remember, higher fluences generate more successful results.
Hope this helps,
Mike.
PS Don’t forget our Masterclass in Manchester next month (April 23rd/24th). Contact me if you wish to attend and learn more about all this stuff. We are also planning another Masterclass in (or near) London in August or September…
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