Many people are worried about ‘burning’ the skin during laser/IPL treatment of hair, tattoos, blood vessels etc. But, what is the actual risk?
Well, we can work this out knowing the skin colour and the applied fluence. Now, as many of you already know, I don’t like the Fitzpatrick Scale because it does not determine skin colour (contrary to popular belief!!). In fact, the Fitzpatrick Scale looks at the skin’s response to ultraviolet light energy and what that exposure may do.
It does NOT tell us the colour of the skin!!
But we can use another method to precisely determine the colour. Using data from an American scientist, Steve Jacques, we can determine the ‘colour’ of the skin by specifying the concentration of melanin in the epidermis.
| Skin colour | Melanin concentration |
| 1 | Up to 10% |
| 2 | 10-16% |
| 3 | 16-23% |
| 4 | 23-33% |
| 5 | 33-43% |
| 6 | >43% |
I use the same numbering system as the Fitzpatrick Scale since this is very familiar to many people. But, as we can see, if you go on holiday and come back with a tan, your melanin concentration will increase – changing your ‘skin colour’. However, your Fitzpatrick number doesn’t change!!
So, having now defined the actual skin colour, how can we calculate the risk of injuring the epidermis with light energy?
To do this, we need to setup a framework. I chose the maximum risk when the alexandrite laser is used on black skin – that is, 755nm on a 43% melanin concentration. This combination yields the highest possible melanin absorption coefficient (how ‘strongly’ the light is absorbed by the melanin).
Out of all of today’s devices and skin colours, this is the ‘riskiest’ possible option! So, using this as the ‘maximum’ risk, it is possible to calculate all the other scenarios, based on this worst-case scenario.
In essence, the values in the graphs above, show the ‘relative’ risk of epidermal melanin damage compared with the alexandrite/black skin scenario. (If anyone can come up with a better idea, please let me know.)
I have also assumed a typical wavelength range of 600 to 1200nm for the IPL treatments, which yields an averaged absorption coefficient similar to that of the diode laser.
The graphs show that the long-pulsed Nd:YAG is, by far, the safest option when considering epidermal damage, for all skin colours. The maximum risk, with this wavelength (1064nm) is only 30% (compared with 100% for the alex/black skin combo).
If we assume that an ‘acceptable’ risk is 50%, or lower, then the diode laser and IPL devices can be safely used for all skin colours up to about 4 – that is up to 33% melanin concentration. However, the graphs appear to indicate that these devices should be used on darker skin colours with great care – i.e. proper skin cooling.
The alexandrite laser fares the worst – due to its wavelength being so highly absorbed by melanin. The 50% safety criteria suggests that those lasers should be used only on paler skin colours, unless plenty of cooling is also used.
Conclusions
The risk graphs only serve to indicate where the risk of epidermal damage is greater. Like all risks, these can be mitigated – with proper skin surface cooling. If sufficient cooling is applied BEFORE the light energy is fired, then the risk of epidermal damage can be significantly reduced. Skin cooling AFTER the application is also necessary since my calculations reveal that more than 90% of the applied energy is not used to cook the hairs!
In summary, when trying to remove hair or blood vessels with light energy, we run the very real risk of damaging the epidermis, dependingon how much melanin it contains. However, this can be properly managed if good skin cooling is also applied.
Hope this makes sense,
Mike.
PS We will discuss this, and much more, in our upcoming MasterClasses. Keep an eye open on our FB and Instagram pages…
Mike Murphy's Blog 
It have to be mentioned that the 755 nm is highly absorbed by the water chromatophore cells, that’s means the water expire from the skin and skin burns
What is a ‘water chromatophore cell’? I’ve not heard of those.
there are three chromophore cells in the body, water, hemoglobin and melanin. 755 nm is also absorbed by the water in the cells. this leads to evaporation of water in the cells, ie. to burn
Actually, there is very little absorption of 755nm in tissue water! It’s much more likely that any steam formation is caused by heat conduction from the melanin rather than by direct absorption.
But that does not necessarily mean that ‘burning’ will occur!
I noticed you graphed the risk using a long pulse YAG. What can we infer if using a quick pulse YAG?
I was specifically looking at hair removal – which requires a long-pulsed Nd:YAG, as you know. This analysis was based on thermal damage and considered only absorption, with no regard for pulsewidth.
However, in terms of wavelength, the risk is the same for both long and short pulses. But we must consider non-linear effects when looking at very short pulses such as nano or picosecond. These will induce a different type of damage, and have a different risk profile.
Thanks for the interesting post. I’m new to lasers and on a steep learning curve. If the Fitzpatrick scale is not helpful when determining melanin concentration in the skin would you suggest a melanin meter instead? We have Cutera Xeo with IPL and Nd:Yag used primarily for skin/ vascular rather than hair removal.
Absolutely. A visual inspection can be quite inaccurate. Plus, as you know, there can be quite a wide variation in skin colour across an individual. I suppose the best thing is to ensure too much cooling, rather than too little!
Thanks for responding so promptly. Which melanin meter do you recommend?
We’re currently finishing one off for market, hopefully soon….