The fluence must be chosen to kill the germ cells in the target follicles. Those are the real targets – not the melanin in the hair shaft. The melanin can be viewed as a surrogate which we can heat using light energy. But, the germ cells do not have a chromophore which we can exploit… Continue reading Why we should NOT reduce the fluence when treating darker skins!!!
Category: Interesting stuff
Where do photons go in the skin?
When photons (light) enter the skin they can undergo only two processes – absorption or scattering. Once a photon is absorbed, its energy is ‘gained’ by the absorbing site. This may be a melanosome in the epidermal basal layer (see figure 1 – ‘Epidermal absorption’). This absorption will transfer the photon’s energy into the melanin… Continue reading Where do photons go in the skin?
SHR/In-motion tehcnique – an update
I read an interesting paper on this topic, last week. It was a clinical study looking into the application of ‘super hair removal’ using a low fluence output from a diode laser. As you may already know, I’m not a big fan of this technique. I feel that it is ‘tricky’ to administer properly and… Continue reading SHR/In-motion tehcnique – an update
How can there be more fluence inside the skin than is applied at the surface???
Here’s a strange thing…. When we fire a laser or an IPL at the skin surface we usually know the fluence that is applied. So, we figure that a 10 J/cm2 will penetrate into the skin and diminish with depth. Well, bizarrely, it doesn’t!! This is entirely due to scattering. So, what is scattering? The… Continue reading How can there be more fluence inside the skin than is applied at the surface???
What is the risk of ‘burning’ the skin with a laser or IPL?
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… Continue reading What is the risk of ‘burning’ the skin with a laser or IPL?
What are the threshold (minimum) fluences needed to ensure successful hair removal?
This is not easy to determine! It depends on the type of device you are using – IPL, diode, alexandrite, Nd:YAG laser. It depends on the depth of the follicles. It depends on the hair colour. I built a computer model to try to calculate these fluences. It considers all of the above, but today… Continue reading What are the threshold (minimum) fluences needed to ensure successful hair removal?
The WRONG way to do laser tattoo removal!
It appears many people are using their tattoo laser wrongly! They are holding it off the skin, up to 10 to 20cm away. This is just wrong!! By doing this they will invariably apply a very small spot diameter at the skin surface which generates a huge fluence (energy density). Such fluences can easily damage… Continue reading The WRONG way to do laser tattoo removal!
Treating blood vessels with an IPL
Blood aborbs light strongly in the region between about 500 and 600nm. The graph below shows this with both oxy- and deoxyhaemoglobin (the red and blue lines). We don’t use the lower wavelengths (below 450nm) because they are too near the blue/ultra-violet part of the spectrum! So, we can selectively target blood vessels using these… Continue reading Treating blood vessels with an IPL
Calculating the optimum intervals between hair removal sessions.
I am often asked, during training, “what is the best time to leave between laser/IPL treatment sessions?” This is actually quite tricky to answer. I wondered about this for some time and then realised that I had to build a computer model to answer it correctly. So, I used Excel and built such a model.… Continue reading Calculating the optimum intervals between hair removal sessions.
Thermal Relaxation Time – The Flaw in Selective Photothermolysis
I gave a talk at this year’s BMLA meeting in Edinburgh. It was on a topic close to my heart – the notion of thermal relaxation times and how they don’t apply to modern-day photo thermal treatments. Here it is… I hope that clears up a few things, Mike.
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