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What are Reactive Oxygen Species?

Reactive oxygen species (ROS) are oxygen containing molecules that have at least one unpaired electron. They are also referred to as free radicals. While ROS are generally regarded as “bad”, in fact they play important roles in our bodies, such as killing invading microorganisms. Short-lived ROS act as signals for the cell to carry out critical functions, and they can have a positive net effect on cellular function. All organisms that breathe oxygen produce ROS, which are a normal part of human physiology. 

However, ROS also have a dark side. Ideally, there is a balance between their production and removal, which is largely mediated by systems of antioxidant enzymes that are found all throughout the body. Dietary antioxidants (such as vitamin E) also help to keep ROS levels in check, and these are found widely in foods such as seeds, fruits, and vegetables. But when production of ROS exceeds their removal, the imbalance can lead to a condition known as oxidative stress. 

What is Oxidative Stress?

Oxidative stress is defined as “an imbalance between production of oxidants [ROS] and antioxidant defenses that may result in damage to biological systems”. It is a more important indicator of health than levels of ROS. An increase in ROS can paradoxically be associated a decrease in oxidative stress, especially if the activity of antioxidant enzymes is increased at the same time. In fact, an increase in ROS acts as a signal to turn up the activity of these enzymes. If the enzyme activity is greater than the increase in ROS, the net oxidative stress will be reduced. Of course, an increase in ROS can also be harmful, particularly when this increase persists over a long period of time. Oxidative stress is associated with most chronic diseases as well as ageing. 

How Does Red Light Therapy Affect ROS & Oxidative Stress?

An increase in the production of ROS has been well documented as being associated with red light therapy. This occurs as a brief burst, with the amount produced being highly dependent on the characteristics of light exposure. The increase in ROS is due to the effects of red light therapy on cellular mitochondria, which is the main mechanism by which red light therapy exerts its beneficial effects. 

This begs the question: what do the ROS produced with red light therapy do in the cell? Are they harmful? How do they affect oxidative stress? The answer is complex, and four lines of evidence show that even though red light therapy can increase ROS production, this does not necessarily translate to an increase in oxidative stress.

First, rather than increasing oxidative stress, the brief increase in ROS production that accompanies red light therapy is often associated with some of its benefits. For example, stem cell therapy is augmented by red light therapy as a direct result of the production of ROS. Similarly, in a review of 14 studies, red light therapy caused ROS levels to increase which helped bone cells to regenerate. An increase in ROS following red light therapy has also been shown to stimulate mitochondrial activity and to induce the growth of new brain cells. Since ROS are well known to act as signals for cells to carry out important functions, brief exposure to red light therapy can have long lasting effects. In fact, the ROS produced following red light therapy have been described as “good” reactive oxygen species. 

Second, studies have clearly shown that markers of oxidative stress can be decreased after red light therapy. Exercise provides a good example. In a comprehensive review of 8 studies, markers of oxidative stress as well as muscle damage, inflammation, and delayed onset muscle soreness were reduced in exercising athletes after treatment with red light therapy. These studies show that regardless of ROS levels, overall oxidative stress can be reduced with light therapy and this is associated with several benefits.

Third, when it comes to oxidative stress, light intensity matters. When wounds are treated with low/moderate intensity red light therapy, markers of oxidative stress initially increase and then decrease dramatically as healing progresses. However, when wounds are treated with high intensity red light therapy, oxidative stress remains high. Similarly, levels of antioxidant enzyme activity increase with low/moderate intensity red light therapy but not with high intensity light. This suggests that low/moderate intensity red light therapy, but not high intensity reduces oxidative stress.  

Fourth, light intensity also matters when it comes to ROS production. In a study of stem cells, treatment with light at 5 J/cm2 increased ROS production while treatment with 2.5 or 10 J/cm2 decreased ROS production. The ROS produced at 5 J/cm2 was also associated with increased tissue regeneration. This has to do with the supply of light energy. A range of light energy will stimulate a response (measured by ROS production), but too little or too much energy will not have the same effect. 

This “biphasic effect” of red light therapy is well known. It is essentially a Goldilocks effect: When the dose of light is too low or too high, it is ineffective, while intermediate doses are beneficial. In fact, high doses of red light therapy may even being harmful. This may be at least partly explained by ROS production – when the light dose is too low, there is no ROS production and no beneficial downstream signaling effects. If the light dose is too high, ROS production is not balanced by their removal, and oxidative stress results. 

How Can I Safely Use Red Light Therapy?

It is clear that treatment with red and near infrared light can produce a brief burst of ROS, and that this increase is directly associated with some of the benefits of red light therapy. However, it is also clear that excessive production of ROS is undesirable and can cause oxidative stress. Given this, how can red light therapy be used in a way that avoids overproduction of ROS? Very simply, it means not overdoing it in terms of light intensity, treatment duration, or session frequency. Here are a few general rules to follow:

  1. Use devices powered by LED, rather than laser light. Most at home devices use LEDs, and as a general rule, these are safer and lower intensity than laser light.
  2. Give preference to LED devices that are low/moderate intensity. The intensity of the sun is 20-40mW/cm2, which is a great target to aim for.
  3. High intensity red light devices should only be used for a few minutes at a time. Low/moderate intensity devices, such as those that mimic the intensity of the sun, can be used for up to 30 minutes.
  4. If using a high intensity device, limit session frequency to a few times per week. Low/moderate intensity devices can be used daily over different body parts, limiting each location to once per day.


Reactive oxygen species are generally understood to be harmful, but it’s clear that this is an oversimplification. When produced in excess, ROS are dangerous, but when production is balanced with removal, they play important roles in cellular functioning. Red light therapy can cause a brief burst of ROS, which usually decreases overall oxidative stress provided the dose of light is not excessive. When it comes to red light therapy, dose matters – and with a few simple considerations, it can be safely used to support health and well-being. 

Dr. Genevieve Newton, DC, PhD  spent close to 20 years as a researcher and educator in the field of nutritional sciences before joining Fringe as its Scientific Director. Gen’s job is to “bring the science” that supports Fringe’s products and education. She is passionate about all things Fringe, and is a deep believer in healing body, mind and spirit using the gifts of the natural world. 

The contents in this blog; such as text, content, graphics are intended for educational purposes only. The Content is not intended to substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your healthcare provider.

For more information about Fringe light products, go to: https://fringeheals.com/shop-all-products/

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