Keeping Cool with Red Light Therapy: Why We Don’t Mix Light and Heat
Is it beneficial to mix heat and light? Can we improve the safety and effectiveness of Photobiomodulation by keeping the tissue cool?
The study of Photobiomodulation has found several reasons why they choose to separate the study of heat (thermal, or photothermal) versus the interaction of light (photobiomodulation).
Photobiomodulation, by definition, is the non-thermal study of the interaction of light with biology.  The science is very clear on this definition, and wish to exclude any heat-inducing methods such as NIR heat lamps and high intensity lasers. 
Simply put, combining heat and light would create too many variables to try to understand. Already there is a difficult time understanding all of the variables and interactions with low-level-light-therapy studies and PBM studies. Imagine if heat was also added as a variable?
So why do we want to separate heat and light?
- High powered lasers and lights are already used for medical applications of ablation, cutting, and tissue removal. We know these are not the type of interactions that we want in Low Level Light Therapy (LLLT) or PBM. 
- Heat effects trigger different mechanisms of action than PBM, and will be difficult to differentiate effects from heat or light without in-depth studies.  This would make the science unclear (or, more unclear than it already is).
- Large Temperature increases in the tissue during PBM have been associated with less desirable outcomes. 
- Tissue optical properties change with temperature, such as absorption and scattering properties.  This can affect the penetration and effectiveness of the light.
- It is well known the maximum safe skin temperature set by the FDA is 41 Celsius, at which, or above will start to cause burns or degradation effects.    Above 41 Celsius, is also the pain threshold and typically the user will stop usage due to discomfort.
What is the possible explanation for the heat effects reducing red light therapy effectiveness?
Assuming the light isn’t so hot that it isn’t causing obvious burning or degradation (above 41° C).
A well-accepted mechanism for PBM benefits is the generation of Reactive Oxygen Species (ROS) to trigger healing effects. Too much ROS, sometimes called Free Radicals, is associated with inflammatory processes. 
This is likely an explanation for the Biphasic Dose Response of Red Light Therapy. That too much red-light therapy, will cause an inhibitory effect and cancel out the benefits that are expected.
It is proposed to monitor skin temperature as an easy way to monitor for biphasic dose and ROS accumulation thresholds.  Is the skin temperature associated with ROS buildup, or too much PBM power - will need to be understood more in the future.
How do we manage temperature in PBM?
- Lower Irradiance, either increasing distance away from the panel, turning off some of the LEDs (if you can control Red/NIR independently), or using a lower powered device.
- Pre-cooling the skin or tissue.
- One group of researchers found better effectiveness and 27.5% better penetration of 810nm laser by applying cryotherapy to the skin before treatment! All they did was use ice for 20 minutes. 
- Using convective cooling air flow (i.e. a fan or air conditioning on the skin [a fan built into the panel only keeps the panel cool and actually blows the hot air around the room]).
- Holding skin temperature constant at 37°C led to good results in one study, while allowing it to heat to 45°C led to a doubling of free-radical formation and half of the antioxidant power. Both were conducted while holding the dose constant. 
- Pulsing or Scanning techniques can give the target tissue time to cool between pulses. Generally, studies that compare Pulse to Continuous Wave find that Pulsing gives better results.
Applying Ice for 20 minuites before PBM could improve penetration and effectiveness. 
There is no doubt, that applying ANY PBM can cause a small temperature increase. However, our body has good mechanisms for thermoregulation and keeping constant temperature. Often, a casual user won’t feel any temperature change.  If you do feel noticeable warming, then that is a sign to use one of the techniques listed above. If you feel a pain or burn sensation, then immediately stop and change your protocol.
Can we still get good effects from PBM and heat?
Of course! It is still possible to have great effects from heat lamps, full spectrum saunas, or even the sun! However, the study quickly becomes complicated and it is difficult to explain the mechanisms.
- One study found that up to 2 degree C temperature increase had no change on the effectiveness of PBM, compared to a group that had 0.2 degree C with temperature control with the same dose PBM.  This shows us that some raise in temperature is normal and OK, but to still be mindful of too high of temperature.
- Another study found that combined heat of 42C and 810nm light had an “additive” effect on the proliferation of stem cells. They were able to isolate heat mechanisms and PBM mechanisms and found that they operate independently! 
What can we conclude from all this?
There is still a lot we don’t know about LLLT or PBM, and one of the biggest questions will be the combination of heat and light.
Of course, when we read any Photobiomodulation study, they are carefully and mindfully designing the study to avoid too much heat, biphasic dose response, and of course the comfort and pain threshold of the patient. If we want to follow the science of thousands of studies on this topic, we should respect the science and also mindfully use our Red Light Therapy to avoid too much heat.
If we want to purely maximize our usage of Photobiomodulation, indicators show that we want to reduce the buildup of heat. And we can even ice our skin for 20 minutes to potentially improve penetration and effectiveness further!
Mixing Photobiomodulation and Heat can of course still confer benefits, and some researchers were able to isolate the different mechanisms and show that the benefits can be “additive.” Meaning that combined heat and light does activate both sets of beneficial mechanisms. Of course, they must be even more vigilant in that case to design the study to understand biphasic dose response of both mechanisms as well.
So we can use PBM in many ways! Combining Cold+Light or even Heat+Light are important modulating factors to help customize the benefits of this therapy! So far, there are very little studies to fully understand these interactions. So, at GembaRed we like to keep things simple, enjoy the process of PBM non-thermally, the way the science has defined it.
Low-Level Light/Laser Therapy Versus Photobiomodulation Therapy
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