Photobiomodulation therapy (PBM) is a treatment that uses red or near-infrared light to stimulate cellular repair, reduce inflammation, and relieve pain. The light, delivered by lasers or LEDs, is absorbed by mitochondria inside your cells, triggering a chain of biological effects that boost energy production and promote healing. It’s a non-invasive, drug-free therapy now used for conditions ranging from chronic pain and wound healing to traumatic brain injury and depression.
How Light Triggers a Cellular Response
The key to PBM lies in your mitochondria, the structures inside nearly every cell that generate energy. A specific protein in the mitochondria called cytochrome c oxidase absorbs photons of red and near-infrared light. Under normal conditions, nitric oxide can bind to this protein and slow it down, reducing your cells’ ability to produce ATP, the molecule that fuels virtually every cellular process.
When light hits cytochrome c oxidase, it knocks that nitric oxide loose. This restores normal electron transport, increases the electrical charge across the mitochondrial membrane, and ramps up ATP production. At the same time, the light triggers a small, controlled burst of reactive oxygen species, which act as signaling molecules. These signals activate pathways that influence gene expression, reduce inflammation, and stimulate tissue repair. In cells already under oxidative stress, PBM actually reduces harmful reactive oxygen species while boosting energy output, essentially helping damaged cells recover their normal function.
Wavelengths and How They’re Chosen
PBM devices use two main wavelength windows: red light in the 630 to 670 nanometer range and near-infrared light between 780 and 940 nanometers. These ranges correspond to the absorption peaks of cytochrome c oxidase, meaning they’re the colors of light most efficiently captured by that protein.
The choice between red and near-infrared depends on the target. Red light is better suited for superficial tissues like skin, gums, and shallow wounds because it doesn’t penetrate as deeply. Near-infrared light passes through more tissue and is preferred for joints, muscles, and the brain. Many clinical devices combine both wavelengths to cover a broader treatment range.
The Dose Matters More Than You’d Expect
One of the most important principles in PBM is that more light is not better. The therapy follows a biphasic dose response, sometimes called the Arndt-Schulz curve. At low doses, light stimulates beneficial cellular activity. At moderate doses, you hit the therapeutic sweet spot. But at high doses, the benefits disappear entirely and the light can actually inhibit healing or damage tissue.
In practical terms, energy densities as low as 2 to 5 joules per square centimeter tend to produce the best results in living tissue. A dose of 50 or 100 joules per square centimeter can worsen outcomes. In wound-healing studies, for instance, 2 joules per square centimeter produced the clearest benefit, while 50 joules per square centimeter actually delayed healing compared to no treatment at all. This is why proper dosing, not just owning a device, is critical to getting results.
Lasers vs. LEDs
PBM can be delivered by either coherent laser light or non-coherent LED light, and the debate over which is superior has been ongoing for years. The core biological effect is a photochemical reaction, not a thermal one, and photons don’t need to be coherent (traveling in perfect sync) to trigger it. For superficial tissues, LEDs appear to work just as well as lasers. One clinical trial on orthodontic pain found that an LED device was effective while the laser was not, likely because the laser delivered too little total energy.
Where lasers may hold an edge is in deeper targets. For transcranial applications, where light must pass through skin, skull, and brain tissue, lasers generally achieve better penetration at the necessary power densities. LEDs, on the other hand, are less expensive and can cover much larger surface areas at once, making them practical for treating broad regions like the scalp or large wounds.
What PBM Treats: Current Evidence
A large umbrella review of randomized clinical trials found moderate-certainty evidence supporting PBM for several conditions. For burning mouth syndrome, a chronic pain condition, PBM produced a large reduction in pain intensity. In knee osteoarthritis, it significantly improved both pain and disability. People with fibromyalgia experienced meaningful improvements in fatigue, stiffness, and overall symptom severity. PBM also showed moderate evidence for increasing hair density in androgenetic alopecia and improving cognitive function.
The therapy promotes wound healing and tissue repair partly by stimulating the proliferation of fibroblasts, the cells responsible for producing collagen and rebuilding connective tissue. Studies using near-infrared wavelengths around 810 to 830 nanometers have consistently shown increased fibroblast growth and attachment, with effects visible within 24 hours of treatment. These findings apply to both soft tissue wounds and tissue growing on implant surfaces.
Brain and Neurological Conditions
Transcranial PBM, where light is applied through the skull to reach brain tissue, is one of the most actively studied frontiers. Clinical trials have shown improvements in cognitive performance for people with mild traumatic brain injury, with one study reporting that sleep duration increased by an average of one hour in chronic TBI patients, for whom poor sleep is a persistent problem. Early research in possible chronic traumatic encephalopathy (CTE) found significant improvements in cognition and mood for ex-football players after 18 treatment sessions.
For depression, multiple clinical trials using near-infrared wavelengths between 810 and 945 nanometers have demonstrated significant improvements on standard depression and anxiety rating scales. Trials in Alzheimer’s disease have shown that 28 consecutive days of treatment improved cognitive and memory ability. Parkinson’s disease patients have experienced measurable improvement in motor symptoms using helmet devices with multiple LED wavelengths. While much of this neurological research is still in relatively early stages with small sample sizes, the consistency of positive findings across different conditions and research groups is notable.
What a Treatment Session Looks Like
PBM sessions are painless. You typically feel nothing, or at most a mild warmth at the treatment site. The light source, whether a handheld laser probe, an LED panel, or a wearable device, is positioned on or near the skin over the target area. Treatment times vary depending on the condition, device power, and area being treated, but individual sites often receive light for one to two minutes, with a full session lasting roughly five to ten minutes when multiple sites are treated.
For musculoskeletal conditions and pain, treatments are commonly administered two to three times per week over several weeks. Neurological protocols may involve daily sessions for a defined period. The number of sessions needed varies widely by condition and severity, and because of the biphasic dose response, clinicians adjust parameters carefully rather than simply extending treatment time.
Safety and Regulatory Status
PBM has a strong safety profile. The American Dental Association notes that no direct contraindications have been formally established. The two standard precautions are to avoid directing light at an obvious tumor mass and to avoid treating the fetus directly during pregnancy, though even these are considered precautionary rather than based on documented harm. There has been some theoretical concern about pulsed laser beams in patients with seizure history, but no adverse events have been reported.
In the United States, PBM devices are classified as Class II medical devices by the FDA, meaning they require a 510(k) premarket notification before being sold. This regulatory pathway applies to devices intended for pain relief, muscle relaxation, and increased local blood circulation. It places PBM in the same general risk category as powered muscle stimulators and therapeutic ultrasound devices.