Photobiomodulation therapy (PBM) uses light wavelengths (600–1070 nm) with energy density (1–150 J/cm²) to penetrate tissues. Shorter wavelengths (600–700 nm) treat superficial tissues, while longer wavelengths (780–950 nm) treat deeper tissues. Whole-body PBM demonstrates systemic effects, improving various health aspects like quality of life, pain, sleep, fatigue, muscle spasms, and psychological factors in fibromyalgia patients. PBM also impacts cerebral blood flow, neuronal function, neuroinflammation, oxidative stress, and neurogenesis. It may influence hormone secretion, reducing pain signaling. Chronic pain, significantly impacting society, affects 13–50% of UK adults and 28.4% of US adults, with high annual costs. Treatment is complex and multifactorial. Chronic pain (lasting ≥3 months) increases premature death risk and cognitive decline. Inflammation, often present in chronic pain, contributes to pain persistence. Oxidative stress plays a role in inflammation, leading to chronic hypersensitivity. This review aimed to synthesize the effects of PBM on chronic musculoskeletal pain and inflammation and analyze the methodological quality of relevant studies.

The literature review section is integrated into the introduction and methodology sections, summarizing existing research on PBM's mechanisms of action, the prevalence of chronic pain and inflammation, and the gaps in the existing literature that motivated this review.

This literature review used a systematic review methodology, adhering to PRISMA criteria. Five databases (PubMed, ProQuest, Web of Science, Scopus, and PEDro) were searched from March to May 2022, using keywords like "low-level laser therapy," "chronic pain," and "inflammation." The PICO strategy guided the search, focusing on patients over 18 with pain/inflammation lasting over 3 months, PBM intervention, comparison with non-PBM treatments, and the effectiveness of PBM on pain and inflammation. PubMed used MeSH terms and additional keywords, while other databases used keyword combinations and Boolean operators (AND/OR). Inclusion criteria were: publication between 2017–2022, peer-reviewed English RCTs, full-text availability, human subjects over 18 with acute or chronic pain or inflammation. Studies not meeting these criteria or duplicates were excluded. Methodological quality was assessed using the PEDro scale (0–10, excellent: 9–10, good: 6–8) and the Internal Validity Score (IVS) (0–7, high: 6–7, moderate: 4–5, limited: 0–3). Studies with poor methodological quality (<4 PEDro) were excluded. Mendeley software managed references.

The search yielded 96,751 articles, ultimately reduced to 11 RCTs meeting the inclusion criteria. Six studies had excellent PEDro scores (9–10), and five had good scores (6–8). Seven studies had high IVS scores (6–7), and four had limited scores (0–3). Five RCTs demonstrated PBM's positive influence on chronic pain, while another showed short-term benefits. Two studies showed marked improvement in inflammation. One study showed no improvement in chronic pain, and another showed no improvement in inflammation. Four studies showed PBM's benefits in acute pain. The review categorized the results by pain type: chronic nonspecific low back pain (varied outcomes), knee osteoarthritis (significant pain and function improvement), fibromyalgia (significant pain reduction in both short and long-term studies but varied outcomes depending on study design), temporomandibular pain and dysfunction (significant pain reduction across treatment groups), and oral pain and inflammation (significant short-term pain and inflammation reduction). The review also included acute pain and post-surgical pain and swelling studies, noting significant pain and inflammation reduction post-PBM. Various questionnaires and scales (VAS, FIQ, RDC, RMQ, NPRS, WOMAC, BAI) were used across studies to measure pain, function, and other relevant outcomes.

This review found limited but generally high-quality evidence supporting PBM's efficacy in managing chronic musculoskeletal pain and acute pain. While several studies showed significant pain reduction following PBM, the long-term effects need further investigation. Similarly, evidence regarding PBM's effect on inflammation is promising but limited. The varied outcomes across studies highlight the need for standardized parameters for PBM application based on the specific condition and patient characteristics. The heterogeneity of chronic musculoskeletal pain conditions and their different pain mechanisms also warrant further research.

This review highlights the generally high methodological quality of existing studies on PBM for pain and inflammation, showcasing its positive effects on chronic and acute pain. However, more research is needed to fully understand its long-term effects, optimize application parameters, and clarify its influence on inflammation. Future research should focus on RCTs investigating PBM in various inflammatory conditions, chronic pain types, and different age groups, especially those under 18. Standardized parameters are also necessary to enhance research comparability and inform clinical practice.

The review's limitations include the limited number of RCTs focusing on PBM's effects on inflammation, the lack of studies defining ideal PBM parameters for different conditions, and the restriction to English-language studies, potentially reducing the scope of the findings. The heterogeneity of chronic musculoskeletal pain conditions, with varying etiologies and pain mechanisms, adds complexity to the interpretation of results. Further research with larger sample sizes and longer follow-up periods is necessary to validate the observed effects.