We often hear, these days, about “pain free” hair removal, with various lasers, usually diodes. But, is it true?
Well, let’s look at this more closely…
The aim with laser, or IPL, treatment of hair is to induce enough heat in the stem cells that stimulate hair growth in the follicles. To do this, we must successfully ‘cook’ those stem cells so that they essentially die.
Now, let’s ask an expert on cooking – Mary Berry – about the correct method to bake a cake. She tells me that we must set our oven temperature to the required cooking level, around 180°C, ensure a proper heating. Then she says we must put our cake mix into that oven for the correct length of time, to ensure that all of the mixture is properly cooked. She told me that this is usually around 60 to 90 minutes, depending on the particular mixture!
So, according to the experts, we must set both the correct temperature AND time to ensure a good result.
We know that the skin’s normal temperature is around 37°C (in the dermis). An excellent study by NASA showed that the thermal pain receptors in the skin trigger at a temperature of 45°C. This is only 8°C above the normal skin temperature!
In other words, an increase of only 8°C is sufficient to cause thermal pain. NASA’s results showed that this is true for virtually everyone – there’s no such thing as a “higher pain threshold” unless those particular nerve sensors are dead!!
So the question is, can such a small temperature rise kill the follicle stem cells? Well, I can literally ‘do the math’ on this one. I have been ‘doing the math’ on laser/IPL heating of hair and blood vessels for over 30 years.
The answer is ‘yes’ – we can kill the stem cells at 45°C. But, that temperature would need to be maintained for around 4.8 minutes!!!
If the temperature is 50°C, that time drops to 43 seconds. At 60°C, the stem cells only require 1.1 seconds to fully cook.
That is how this works – as the temperature increases, the time required to destroy the proteins reduces exponentially!!
At 70°C, the time required is only 35 milliseconds (at this point, all my former trainees should be saying ‘Ahhhh!!!’). This tells us that we should probably use higher temperatures, for shorter times to achieve the desired goal. The way to do this is to use a higher fluence (energy density – “Joules” as many call it) to induce higher temperatures in the follicles.
Using a combination of higher fluences with shorter pulses should yield better results (this combination results in less thermal damage to the surrounding collagen). But the cost of this is some PAIN!!!
However, it’s not all bad news – we can mitigate against this pain if we use proper cooling – before, during and after each treatment. I did a blog post on this earlier this year, with a video showing how to do this correctly (https://mikemurphyblog.com/2022/01/07/the-best-way-to-cool-the-skin-during-laser-ipl-treatments/).
Unfortunately, all this suggests that the SHR technique cannot achieve good results without overheating! I have long suspected that this technique was inefficient. It seems that the ‘pain free’ aspect of this technique merely confirms this…
So, we have a choice:
do we use a ‘pain free’ technique which doesn’t appear to work well?, or
do we use higher fluences, which generate higher temperatures, but require much shorter times?
The answer, to me, is obvious.
The only real ‘pain free’ hair removal is when we use scissors….
Hope this helps,