Red Light Therapy

Red light therapy, more formally photobiomodulation (PBM) and previously known as low-level laser therapy, is a noninvasive form of phototherapy that uses wavelengths in the red light (620-700 nm) portion of the visible spectrum and the near-infrared (700-1440 nm) spectrum. ^[1] It is often administered through low-level lasers or light-emitting diodes and is applied to a range of dermatologic and nondermatologic conditions. ^[1] The field, sometimes known as photobiomodulation, has broadened over time to include light-emitting diodes and other light sources beyond lasers, spanning many wavelengths in the red and near infrared. ^[2]

Photons from red and near-infrared light are absorbed by endogenous photoreceptors including mitochondrial cytochrome c oxidase, whose activation modulates ATP production, generates reactive oxygen species, and alters intracellular calcium levels. ^[1] Red to near-infrared light can stimulate complex IV of the mitochondrial respiratory chain (cytochrome c oxidase) and increase ATP synthesis, with light absorption by ion channels releasing calcium and activating transcription factors and gene expression. ^[3] It is hypothesized that inhibitory nitric oxide can be dissociated from cytochrome c oxidase, thereby restoring electron transport and increasing mitochondrial membrane potential. ^[4] The modulation of ATP, reactive oxygen species, and calcium promotes activation of signaling pathways that contribute to downstream effects on cellular proliferation, migration, and differentiation. ^[1]

An evidence-based consensus of an international multidisciplinary panel concluded that photobiomodulation is a safe treatment modality for adult patients and that red light PBM does not induce DNA damage. ^[5] The same consensus judged PBM an effective treatment option for peripheral neuropathy, androgenic alopecia, wound ulcers of multiple etiologies, decubitus ulcers, pain from diabetic foot ulcers, and acute radiation dermatitis. ^[5] A systematic review and meta-analysis of 22 randomized placebo-controlled trials with 1063 participants found that low-level laser therapy significantly reduced pain and disability in knee osteoarthritis, with no adverse events reported. ^[6] A separate systematic review and meta-analysis of randomized controlled trials found that low-level laser therapy significantly reduces pain and disability in lower-extremity tendinopathy and plantar fasciitis in the short and medium term, though long-term data were not available. ^[7] There is a considerable body of evidence supporting the efficacy of PBM for preventing oral mucositis in patients undergoing radiation therapy for head and neck cancer, chemotherapy, or hematopoietic stem cell transplantation. ^[8] In a meta-meta-analysis of myopia control strategies, repeated low-level red-light therapy demonstrated clinically significant effects on slowing both axial length elongation and spherical equivalent refraction progression.

PBM is generally well-tolerated and safe, with erythema being the most common and self-limiting adverse cutaneous effect. ^[1] More than 50 years after its discovery there is still no agreement on the parameters and protocols for clinical application, and the wide range of applicable parameters has in some cases led to contradictory results. ^[10] Effective therapy depends on treatment parameters such as fluence, treatment duration, and output power, and cells or tissues with higher numbers of mitochondria tend to respond to lower doses of light than those with fewer mitochondria. ^{[1] [10]}