Red light therapy shows genuine promise for reducing certain types of inflammation, particularly in joints and soft tissue. The strongest evidence comes from studies on knee osteoarthritis, where multiple meta-analyses have found meaningful reductions in pain and stiffness. But the results aren’t universal. How well it works depends heavily on the type of inflammation, the dose of light used, and where it’s applied on the body.
How Red Light Affects Inflamed Tissue
Red and near-infrared light (roughly 600 to 900 nanometers in wavelength) penetrates the skin and is absorbed by an enzyme inside your mitochondria, the energy-producing structures in every cell. This enzyme normally helps convert oxygen into usable energy in the form of ATP. When it absorbs red or near-infrared light, it ramps up that energy production.
The extra ATP triggers a cascade of cellular signals. Calcium gets released, signaling molecules called second messengers activate, and gene expression shifts in ways that can dial down the inflammatory response. The light also prompts cells to release small amounts of nitric oxide, which improves local blood flow and helps clear inflammatory byproducts from damaged tissue. This combination of better energy supply, improved circulation, and altered cell signaling is what gives red light therapy its anti-inflammatory potential.
What the Evidence Shows for Joint Inflammation
Knee osteoarthritis is the condition with the most clinical data behind red light therapy. Several meta-analyses of randomized controlled trials have found that it can significantly reduce joint pain and improve stiffness and physical function scores in people with knee osteoarthritis. One large meta-analysis identified an optimal protocol: wavelengths between 785 and 860 nanometers at 4 to 8 joules per treatment spot, or 904 nanometers at 1 to 3 joules per spot.
A more recent analysis found that applying red light twice a week for a total of 10 to 16 sessions, using wavelengths between 640 and 905 nanometers at 4 to 8 joules per point, produced meaningful pain relief. That said, not every study agrees. A 2015 systematic review of nine randomized trials found no significant improvement in pain, stiffness, or function scores compared to a control group at 12 weeks after treatment. The difference in results likely comes down to dosing. Studies that used the wrong wavelength or energy level often showed little benefit, while those hitting the right parameters saw real improvements.
This is a critical point: red light therapy for inflammation is dose-dependent in both directions. Too little energy does nothing. Too much can actually increase inflammation rather than reduce it, a phenomenon researchers call the biphasic dose response.
Systemic Inflammation Is a Different Story
If you’re hoping red light therapy will lower body-wide inflammatory markers like C-reactive protein or interleukin-6, the evidence is much thinner. Studies looking at blood levels of these markers after light therapy have generally not found significant reductions. In one study of patients with treatment-resistant depression who received bright light therapy, interleukin-6 levels actually increased slightly after four weeks, particularly in those who responded well to the treatment.
This doesn’t mean red light therapy is useless for systemic conditions. It means its anti-inflammatory effects appear to be primarily local, working best on tissue the light can actually reach. Shining a red light panel on your chest won’t meaningfully change what’s happening in your gut or deep organs. For localized inflammation in muscles, joints, tendons, or skin, the picture is more encouraging.
Practical Dosing Guidelines
Getting the dose right matters more with red light therapy than most people realize. The general target for an anti-inflammatory session is 10 to 15 joules per square centimeter of skin. At a power density of 55 to 87 milliwatts per square centimeter, you can reach that dose in about three minutes per treatment area. Power density should stay below 300 milliwatts per square centimeter for red and infrared light to avoid heating tissue.
For inflammation specifically, a common approach is daily sessions for the first two weeks, then tapering to two or three sessions per week for ongoing maintenance. Each session targets the specific area of inflammation, holding the device a few inches from the skin or in direct contact, depending on the manufacturer’s instructions. Treatments for joint pain in clinical trials typically ran 10 to 16 total sessions at twice per week, so expect to commit to at least a month before judging whether it’s working for you.
Who Should Be Cautious
Red light therapy is considered low-risk for most people. It doesn’t use ultraviolet light, so it won’t burn or tan your skin. The most common side effect is mild warmth at the treatment site. However, if you take any medication that increases sensitivity to light, including certain antibiotics, antifungals, and acne treatments, you should avoid it. People with a history of skin cancer or eye disease should get clearance from their doctor first. And because the light can be intense enough to damage the retina with direct exposure, proper eye protection is essential during treatment, especially with near-infrared wavelengths you can’t see.
What Red Light Therapy Can and Can’t Do
Red light therapy is a reasonable option for localized inflammatory pain, especially in superficial joints and soft tissue. The evidence is strongest for osteoarthritis of the knee, with credible data showing reduced pain and improved function when the right wavelength and energy dose are used. It also has a favorable safety profile compared to anti-inflammatory medications, which carry risks of stomach bleeding, kidney problems, and cardiovascular effects with long-term use.
Where it falls short is as a treatment for systemic or deep-organ inflammation. Conditions like inflammatory bowel disease, widespread autoimmune flares, or chronic low-grade systemic inflammation driven by metabolic dysfunction aren’t well-served by a therapy that works primarily on tissue within a few centimeters of the skin surface. For those situations, the fundamentals of anti-inflammatory eating, regular exercise, adequate sleep, and appropriate medical treatment remain far more impactful than any light device.