Mechanisms and clinical application of photobiomodulation in pain therapy: a mini review

Chronic pain remains a major clinical challenge, creating a need for safe, non-pharmacological interventions. This narrative mini-review examines two light-based approaches that differ in their sites of action and treatment parameters: visual-light exposure and local red or near-infrared light-emitting diode photobiomodulation. Visual-light exposure acts through retinal and central neural circuits, including pathways involving the ventrolateral geniculate nucleus, dorsal raphe nucleus, periaqueductal gray, medial secondary visual cortex, and anterior cingulate cortex. Its effects are wavelength- and context-dependent. Green light has generally produced antinociceptive effects in preclinical studies and preliminary clinical benefits in migraine, whereas visual exposure to red light has predominantly been associated with increased pain. White light can either facilitate or suppress pain depending on irradiance, exposure duration, circadian timing, and clinical context. By contrast, locally applied red or near-infrared LEDs have reduced pain in several preclinical models and limited clinical studies through peripheral opioid signaling, modulation of nitric oxide and nociceptor sensitization, and anti-inflammatory and antioxidant effects. The opposing effects of visual and local red light indicate that wavelength alone does not determine the pain response; exposure route, target tissue, dose, timing, and baseline pain state are also critical. Although visual-light interventions and local LED PBM appear promising as adjuncts to conventional treatment, the evidence remains limited by heterogeneous protocols, small clinical samples, and incomplete dosimetric reporting. Future studies should use standardized parameters, rigorous controls, and condition-specific protocols to establish efficacy and identify patients most likely to benefit.