Natural light profoundly affects our biology, from how well we sleep, to our brain function and immune response. The ancient Egyptians used solar radiation to disinfect and heal chronic wounds and ulcers as far back as 5000 BC, making light therapy one of the oldest therapeutic methods used by humans.
Now evidence is growing that by delivering specific wavelengths of red and near-infrared laser light to precise areas of the body, it is possible to fine tune biochemical processes such as mitochondrial function and cell signalling to aid cell rejuvenation and healing.
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This technique is known as photobiomodulation. It was once solely used in hospitals and clinics to reduce pain and inflammation, or promote healing of wounds, deeper tissues and nerves, as well as preventing tissue damage. However, photobiomodulation is now highly commercialised, with low-level laser therapy devices developed to allow consumers to harness its powers at home in a bid to improve the appearance of their skin.
Low-level laser therapy devices do not work like traditional ablative lasers used in the skin therapy industry. Ablative lasers create thermal micro injuries to the epidermis and heat the underlying dermis to stimulate collagen production. Instead, the new devices use laser light at much lower intensities to stimulate light sensitive molecules involved in the cascade of skin rejuvenation processes.
Laser light can penetrate further into the skin than non-coherent light because of a phenomenon known as speckle. Whenever light enters a random medium, like the skin, it is scattered and absorbed, the precise wavelength determining how far it can travel (see diagram below).
But laser light has an additional property called coherence that causes it to interfere, either combining to create a bright patch or cancelling out. In skin (and other random media), this interference pattern is random—that’s speckle. But crucially, where the scattered light combines to create speckle, it can penetrate deeper into the tissue at intensity thresholds sufficient to initiate biochemical cascades. By comparison, non-laser sources do not generate speckle.
“If you want to rebuild the skin, the light has to arrive at the base layer, where regeneration takes place with sufficient power,” says Lucy Goff, founder of LYMA, a wellness company that has developed a low-level laser therapy device for home use.
In a study published in Aesthetic Surgery Journal, aesthetic surgeon Graeme Glass, who operates at Sidra Medicine, Qatar and is LYMA Aesthetic Director, says some experimental evidence suggests laser light is more effective in deeper target tissue but that more evidence is needed to inform clinical practice.
Various kinds of evidence has been building for some time. In 1967, Endre Mester at the Semmelweis Medical University in Hungary observed that defocused red laser light can enhance healing in mouse skin. While testing the safety of this light, he first observed an unexpected acceleration in hair regrowth, and later, enhanced wound healing. However, it has taken decades to shed more light on its reparative effects.
One challenge is understanding the mechanism behind photobiomodulation. One idea is that red laser light can trigger microscopic convection currents within cells that help mix and spread biochemical reactants and nutrients. Another possibility is that near infrared light triggers a complex cascade of events in mitochondria, the chemical factories inside a cell that generate most of its chemical energy in the form of a molecule called adenosine triphosphate or ATP. The light is thought to stimulate an enzyme involved in this cascade called cytochrome c oxidose, which accelerates synthesis of ATP. Glass explains: “Effectively, you’re supercharging the mitochondria to make more ATP, which helps cell regeneration.”
Photobiomodulation is also involved in wound healing. A possible mechanism here is that laser light may change the affinity of proteins called transcription factors that help turn specific genes ‘on’ or ‘off,’. “As a result, genes that are responsible for senescence [cell death] and decline have been shown to be switched off, and genes involved in cell proliferation, survival, tissue repair, and regeneration are switched on,” Glass says.
There is also evidence that photobiomodulation can reduce inflammation through a separate pathway. Some trials have shown low-level laser therapy reducing inflammation in joint pain, possibly by inhibiting COX-2, an enzyme involved in inflammation and pain.
Many people opt for low-level laser therapy in the hope of preventing, or smoothing wrinkles. “As we age, we gradually lose the natural process of cell turnover,” says Glass.
He believes that photobiomodulation influences skin cells called fibroblasts that produce collagen. In these cells, the cascade of events stimulated by laser light increases the gene expression for collagens and the production of polysaccharides. These sugars cause the cell to draw in water by osmosis making the skin appear firmer and more elastic. In theory, this should reduce the appearance of wrinkles and lines and some studies appear to back this up.
Nevertheless, more evidence is needed. After hundreds of clinical studies and decades of use, the question is not whether low-level laser therapy has biological effects, but how. In particular, researchers need to better understand the optimal parameters of these laser light sources for different uses.
That’s difficult because many trials involve small patient cohorts and are often funded by industry and so are not independent. “There is ample scope to improve the quality of evidence,” says Glass. He believes well-designed, adequately powered, independent clinical trials will help answer some of the unresolved questions and enable the full potential of this therapy to be realised.
In the meantime, low-level laser therapy’s commercial applications are growing, with home-use laser devices, such as the LYMA Laser entering the market. Paul Clayton, LYMA director of science, recognised the opportunity to engineer a portable low-level laser therapy device with no risk of skin damage. “You can use it around your eyes to focus on crow’s feet and it’s perfectly safe,” he says.
In short, low-level laser therapy is here to stay. “Photobiomodulation is a real phenomenon,” says Glass. “The challenge is to prove its therapeutic utility in retrospect.”
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