Efficacy of Photobiomodulation Therapy in the Treatment of Pain and Inflammation: A Literature Review

Photobiomodulation therapy (PBM) uses light wavelengths typically between 600–1070 nm with energy densities from 1–150 J/cm². This range penetrates tissue effectively; 600–700 nm is used for superficial tissue, and 780–950 nm for deeper tissues. PBM has been associated with improvements in quality of life, pain, sleep, fatigue, stiffness, psychological factors, tissue elasticity, circadian rhythms, and tender points, including in fibromyalgia, and may affect cerebral blood flow, neuronal bioenergetics, neuroinflammation, oxidative stress, apoptosis, neurogenesis, and intrinsic brain networks. PBM may also modulate hormones such as serotonin and endorphins, potentially reducing pain signaling. Chronic pain (pain persisting ≥3 months) is common, particularly in older adults, and is associated with substantial personal and societal burden. Inflammation contributes to many chronic pain conditions; oxidative stress-related mediators (chemokines, transcription factors, microRNAs, cytokines) drive low-grade inflammation (LGI), peripheral and central sensitization, and chronic musculoskeletal pain. Although PBM has been used to treat pain and inflammation, there has been no synthesis of its effects combined with a quality assessment of the evidence. This review aims to evaluate PBM effectiveness for chronic musculoskeletal pain and inflammation and appraise the methodological quality of the evidence.

Background literature highlights PBM’s local and systemic effects, including improved cerebral blood flow, neural bioenergetics, reductions in neuroinflammation and oxidative stress, and modulation of neurotrophic factors and intrinsic brain networks. Hormonal modulation (serotonin, endorphins) may attenuate pain signaling. Epidemiological data emphasize the high prevalence and impact of chronic pain in older adults, with significant societal costs and complex management needs. Inflammation, driven by oxidative stress, is implicated in chronic hypersensitivity and persistent pain through cytokines and other mediators; prolonged immune dysregulation leads to low-grade inflammation and central sensitization. Prior studies have explored PBM across musculoskeletal and orofacial conditions (e.g., fibromyalgia, low back pain, osteoarthritis, temporomandibular disorders), but parameters and protocols vary widely. A gap identified is the absence of a focused synthesis on PBM’s effects on chronic pain and inflammation alongside methodological quality appraisal of recent RCTs.

Design: Literature review of randomized clinical trials (RCTs) using systematic-review methodology aligned with PRISMA guidelines. Databases: PubMed, ProQuest, Scopus, Web of Science, and PEDro. Timeframe: Searches conducted March–May 2022; inclusion limited to publications from January 2017 to May 2022. Search strategy: MeSH and keyword combinations including low-level light/laser therapy, photobiomodulation, chronic pain, inflammation, metabolism, physiotherapy; Boolean operators AND/OR. PICO: Population—adults >18 years with pain >3 months or inflammation; Intervention—PBM to reduce pain/inflammation; Comparison—PBM vs sham or other control; Outcomes—effectiveness of PBM strategies on chronic pain and inflammation. Inclusion criteria: International, peer-reviewed RCTs in English; human subjects; access to full text; participants with acute or chronic pain, musculoskeletal pathology causing chronic pain, and/or edema/inflammation. Exclusion: Not meeting criteria, duplicates, absence of PBM, or lacking results/interpretation. Study management: References managed with Mendeley. Quality appraisal: PEDro scale (0–10; item 1 non-summed); Internal Validity Score (IVS) comprising PEDro items 2,3,5–9 (0–7). Thresholds: PEDro—9–10 excellent, 6–8 good, 4–5 regular, <4 poor (poor-quality trials excluded); IVS—6–7 high, 4–5 moderate, 0–3 limited. Yield: Initial search identified 96,751 records; screening and eligibility assessment produced 11 RCTs for inclusion. Data extraction: Study characteristics, interventions, parameters, outcomes, and results; PRISMA flow described (Figure 1).

- Evidence base: 11 RCTs included. Methodological quality: Six rated excellent and five good on PEDro; IVS indicated seven high and four limited internal validity studies. - Chronic pain: Five RCTs showed PBM significantly reduces chronic pain; one RCT showed benefits only short term; one RCT reported no improvement in chronic pain. Examples: • Nonspecific chronic low back pain—PBM/LLLT improved pain and function across 3 months vs placebo (p < 0.001); another RCT showed short-term improvements with deterioration by 1–3 months without continued exercises; PBM modulated PGE2 (p = 0.04) though IL-6 and TNF-α changes did not translate to significant pain reductions in that trial. • Knee osteoarthritis—significant improvements in pain-related outcomes and function with PBM/LLLT-based protocols (p < 0.05). - Inflammation: Two RCTs showed PBM significantly reduced inflammatory biomarkers; one RCT showed no significant change. Examples: • Post-arthroplasty PBMT reduced serum IL-6, IL-8, and TNF-α vs placebo (p < 0.05). • In chronic low back pain, PBM reduced PGE2 (p = 0.04), but IL-6 and TNF-α did not change significantly vs control. • Periodontal/orthodontic setting—LLLT reduced gingival inflammation within 24 h (p = 0.00). - Acute pain: Four RCTs reported PBM benefits in acute pain. Examples: • Post-endodontic pain—PBMT reduced pain more than ibuprofen 600 mg in first 24 h (p < 0.001). • Post-arthroplasty—PBMT significantly reduced acute pain (p < 0.05). • Orthodontic pain—LLLT reduced pain at 6 h and 24 h (p = 0.01) and at 3 days (p = 0.03, marginal). - Condition-specific highlights: • Fibromyalgia—PBM and PBM+exercise improved pain thresholds and reduced tender points in long term (10 weeks); immediate improvements favored PBM over exercise; orofacial pain reduced significantly (p = 0.0001) with PBM comparable to anesthetic infiltration, with better perceived well-being in PBM group. • Temporomandibular disorders—PBM, manual therapy, and combined therapy all reduced pain and anxiety (p < 0.001), with no significant differences between groups. - Overall: PBM demonstrates beneficial effects on chronic pain and inflammatory markers, with stronger evidence for short-term outcomes; heterogeneity in protocols and outcomes limits generalizability.

The review indicates that PBM can reduce pain and modulate inflammatory processes across musculoskeletal and orofacial conditions, addressing the question of its efficacy in chronic pain and inflammation. Consistent short-term benefits were observed in chronic low back pain, knee osteoarthritis, fibromyalgia, TMD, and dental/orthodontic contexts, with biomarker changes (e.g., reductions in IL-6, IL-8, TNF-α, and PGE2) supporting anti-inflammatory mechanisms. However, effects on inflammation were not uniform across studies, and sustained long-term benefits were less consistent, with some trials showing attenuation of effects after therapy cessation. Variability in PBM parameters (wavelengths, energy densities, application sites, session frequency), heterogeneity of patient populations and conditions, and diverse outcome measures complicate direct comparisons and meta-analytic synthesis. Despite these limitations, the methodological quality of included trials was generally high, strengthening confidence in observed effects. The findings support PBM as a non-invasive adjunct for managing pain and inflammation, while underscoring the need for standardized protocols and longer-term follow-up to determine durability of effects and identify optimal dosing regimens.

The collected RCTs are generally of high methodological quality and indicate that PBM influences pain and chronic pain symptoms, with evidence of short-term efficacy across several conditions. Evidence for PBM’s anti-inflammatory effects is promising but limited to a small number of RCTs; more robust, standardized, and long-term studies are needed to confirm sustained benefits and define optimal parameters by condition. Future research should include well-designed RCTs targeting chronic musculoskeletal pain and diverse inflammatory conditions, develop consensus on PBM parameters, and extend evaluations to underrepresented populations, including elite athletes and individuals under 18 years of age.

- Limited number of RCTs specifically addressing inflammation and chronic musculoskeletal pain. - Heterogeneity of study populations, conditions, and pain mechanisms, limiting generalizability. - Lack of standardized PBM parameters (wavelength, energy density, dosage, frequency) across studies. - English-only inclusion may introduce language bias. - Some studies showed only short-term benefits with limited long-term follow-up data, and several had limited internal validity by IVS.