Red light therapy reduces pain through two primary mechanisms: it triggers the release of nitric oxide, which widens blood vessels and improves circulation to injured tissue, and it stimulates energy production inside cells, which accelerates repair. The therapy uses specific wavelengths of red and near-infrared light, typically between 630 and 850 nanometers, that penetrate skin and reach deeper structures like muscles, joints, and connective tissue. The result is reduced inflammation, less swelling, and measurable improvements in pain for conditions like osteoarthritis and exercise-related soreness.
What Happens Inside Your Tissue
When red or near-infrared light hits your skin, it passes through the surface layers and is absorbed by a protein inside your cells’ mitochondria, the structures responsible for producing energy. This protein sits at the end of the cell’s energy production chain, and when light activates it, the cell ramps up its output of ATP, the molecule every cell uses as fuel. More energy means faster repair of damaged tissue, reduced oxidative stress, and a shift away from inflammatory signaling.
The second major pathway involves nitric oxide. Red light at around 670 nanometers causes the inner lining of blood vessels to release stored nitric oxide precursors. Nitric oxide is a signaling molecule that relaxes blood vessel walls, widening them and increasing blood flow to the treated area. In animal studies, just 5 to 10 minutes of red light exposure on a small area produced measurable vasodilation, and blood flow remained elevated for 30 minutes after the light was turned off. With repeated daily treatment over 14 days, researchers observed a steady, significant increase in circulation to the treated limb. Better blood flow means more oxygen and nutrients reaching damaged tissue, and faster removal of inflammatory waste products.
Which Wavelengths Reach Which Tissues
Not all red light penetrates to the same depth, and the wavelength determines what structures the light can actually reach. The therapeutic range falls between 630 and 850 nanometers. Within that window, shorter wavelengths in the visible red range (630 to 700 nm) are absorbed closer to the surface, making them useful for skin conditions, superficial wounds, and surface-level inflammation.
Near-infrared wavelengths (780 to 1,000 nm) penetrate significantly deeper. According to the German Federal Office for Radiation Protection, near-infrared light can reach up to about 5 millimeters into the skin, passing through the outer layers and into the fatty tissue beneath. In practice, this means wavelengths like 810 and 850 nm can deliver energy to muscles, joint capsules, and connective tissue. The 850 nm wavelength is widely used in joint and recovery applications, while 810 nm has been studied more heavily for nerve-related pain.
For someone with knee pain from osteoarthritis, a surface-level red wavelength alone wouldn’t reach the joint. Near-infrared light in the 810 to 850 nm range is necessary to get energy to the structures that are actually inflamed.
Pain Relief in Osteoarthritis
The strongest evidence for red light therapy and pain comes from osteoarthritis research, particularly for the knee. Meta-analyses of clinical trials show improvements of up to about 14 points on a 100-point visual analog pain scale following treatment for knee osteoarthritis. That’s a moderate but meaningful reduction, roughly equivalent to the difference between pain that limits your daily activities and pain that’s noticeable but manageable.
Results across individual trials are variable. Some patients experience significant relief while others see minimal change, which likely reflects differences in treatment protocols, the severity of joint damage, and individual biology. Red light therapy does not rebuild lost cartilage or reverse structural damage in a joint. What it appears to do is reduce the inflammatory environment around the joint, improve local circulation, and decrease the pain signaling that makes the joint hurt during movement.
Muscle Soreness and Recovery
For exercise-induced muscle soreness, the delayed aching you feel 24 to 72 hours after intense activity, red light therapy shows a moderate effect on reducing how much that soreness builds up. In a study on runners who received LED therapy between two 40-minute time trials, the treatment group experienced less of an increase in soreness before their second run compared to controls.
However, the therapy did not change objective recovery markers like creatine kinase (an enzyme that leaks from damaged muscle fibers) or lactate levels. It also didn’t improve running performance, maximum heart rate, or perceived exertion during exercise. This suggests red light therapy may help with how sore you feel without necessarily speeding up the underlying structural repair of muscle tissue. For recreational athletes, that reduction in perceived soreness can still matter for training consistency and comfort, even if it doesn’t translate to faster performance recovery.
How Sessions Are Typically Structured
The World Association for Photobiomodulation Therapy recommends an effective dose range of 1 to 4 joules per treatment point, with the specific dose depending on how deep the target tissue sits beneath the skin. Shallower targets like tendons near the surface need less energy, while deeper joints or thick muscle groups need more. The therapeutic window is fairly forgiving, with effective results seen within about 50% above or below the recommended dose. Power density should stay at or below 100 milliwatts per square centimeter to avoid heating the tissue rather than stimulating it.
In practical terms, most treatment sessions last somewhere between 5 and 20 minutes per area, depending on the device’s power output and the size of the treatment zone. Conditions like chronic joint pain typically require multiple sessions per week over several weeks or months before results stabilize. A single session can produce temporary pain relief and improved blood flow, but the cumulative effect of repeated treatments is where more lasting changes appear, as seen in the 14-day vasodilation studies.
Home devices vary enormously in power output. A small handheld LED panel delivers far less energy per minute than a clinical-grade laser, meaning longer session times are needed to reach the same dose. If you’re using a consumer device, check its power output in milliwatts per square centimeter and calculate how long you need to hold it over the area to reach the 1 to 4 joule range.
Safety Considerations
Red light therapy is generally well tolerated, with a low risk of side effects when used at recommended doses. The light wavelengths used (630 to 850 nm) fall outside the ultraviolet range, so they don’t carry the skin cancer risks associated with UV exposure. Overuse can cause mild skin warming, but tissue damage from red or near-infrared light at therapeutic doses is rare.
The photosensitivity concerns that apply to UV-based light therapies are largely irrelevant here. Most photosensitizing medications, including common ones like certain antibiotics, blood pressure drugs, and anti-inflammatory medications, cause reactions primarily in the ultraviolet A range, not in the red or near-infrared spectrum. That said, if you’re taking any medication known to increase light sensitivity, it’s worth mentioning your interest in red light therapy to your prescriber, particularly if you’re using a high-powered device over large body areas.
Eye protection is important when using devices that emit near-infrared light, since this wavelength is invisible and your blink reflex won’t protect you from a beam directed at your face. Most clinical and home devices come with appropriate goggles.