Scientific Review of Soft Laser Therapy

The beginnings: Endre Mester and the accidental discovery

The history of soft laser therapy began in 1967 in Budapest, when Professor Endre Mester obtained an unexpected result during an experiment. He originally investigated whether a low-energy ruby laser would cause tumors in mice. To his surprise, the irradiated area did not develop tumors but showed accelerated hair growth and wound healing.

This accidental discovery launched the science of photobiomodulation. Professor Mester's further research laid the theoretical foundations of the method, and his work has led him to be regarded worldwide as the "father of laser biomodulation."

How does the soft laser affect cells? – The mechanism of action

Soft laser does not act via thermal effects – that is, biological changes are due not to heat but to photochemical reactions of light. Scientific consensus identifies the main target molecule as the enzyme cytochrome c oxidase located in the mitochondria of cells.

The mitochondrial effect

When red or near-infrared light (600–1100 nm) reaches cells, the cytochrome c oxidase enzymes in mitochondria absorb the photons. This process leads to:

• Increased ATP production – more "fuel" for cells
• Release of nitric oxide (NO) – improves local blood flow
• Modulation of reactive oxygen species (ROS) – activates cell signaling
• Influence on gene expression – anti-inflammatory and regenerative pathways

These molecular changes cascade into clinically observable effects: pain reduction, inflammation attenuation, and faster tissue regeneration.

The biphasic dose–response relationship

One of photobiomodulation's most important characteristics is the biphasic dose–response curve, known as the Arndt‑Schulz law. This means:

• Too low a dose → no effect
• Optimal dose → maximal therapeutic effect
• Too high a dose → effect diminishes or inhibitory effects occur

Zein and colleagues' 2018 comprehensive review (PMC8355782) analyzed in detail the relationship between parameters and efficacy, concluding that optimal parameters are tissue- and indication-dependent.

The evidence pyramid – How to evaluate the evidence?

Scientific evidence is not all equal. In medical research we arrange levels of evidence in a hierarchy:

For soft laser therapy there is now a considerable amount of level I and II evidence – although the strength of evidence varies by indication.

The comprehensive evidence: Umbrella review 2025

In 2025 the most comprehensive analysis to date on the efficacy of photobiomodulation was published (Son et al., PMC12326686). This is an "umbrella review" – a meta-analysis of meta-analyses – which examined 35 different health outcomes based on randomized controlled trials.

Key findings

Using the GRADE methodology, the assessment found:

• Moderate-certainty evidence (6/35 outcomes, 17%) – strong scientific support for these indications
• Low-certainty evidence (20/35 outcomes, 57%) – promising results but further research needed
• Very low-certainty evidence (9/35 outcomes, 26%) – early-stage research

The review confirmed PBM's potential to support pain relief, reduce inflammation and aid tissue regeneration, while emphasizing the need for further high-quality research.

Evidence summary by indication

Knee osteoarthritis

One of the most well-researched areas. Several meta-analyses have evaluated the efficacy of soft laser in knee osteoarthritis:

Stausholm et al. (2019, PMID: 31662383) – 22 RCTs, 1063 patients:

• Pain reduction: 14.23 mm on the VAS compared with placebo (p < 0.05)
• With recommended dose: 18.71 mm VAS improvement at the end of treatment
• At follow-up (2–4 weeks later): 31.87 mm VAS improvement
• Functional improvement was also significant

2024 network meta-analysis (PMC11455796) – 13 RCTs, 673 patients:

• LLLT was significantly better than placebo for pain reduction (SMD = 0.96)
• Optimal wavelengths: 785–860 nm or 904 nm
• The 808 nm laser showed better improvement in muscle strength than 660 nm

Evidence level: ⭐⭐⭐⭐ (strong, also recommended by WALT)

Rheumatoid arthritis

The Cochrane Collaboration has evaluated the efficacy of soft laser for rheumatoid arthritis several times:

• Favorable effects on short-term pain reduction and morning stiffness
• Few adverse effects compared with placebo
• Efficacy depends on wavelength, dose and application technique

Evidence level: ⭐⭐⭐ (moderate)

Neck pain

Multiple systematic reviews and meta-analyses have examined soft laser for acute and chronic neck pain:

• Acute neck pain: RR 1.69 (95% CI 1.22–2.33) – significantly better than placebo
• Chronic neck pain: WMD 19.86 mm VAS (95% CI 10.04–29.68)
• Effects may persist for up to 22 weeks

Evidence level: ⭐⭐⭐⭐ (strong for chronic pain)

Low back pain

Evidence is mixed for chronic non-specific low back pain:

• Some meta-analyses report positive results
• The Cochrane review (2007) concluded "insufficient evidence"
• Newer studies show more promising results but with heterogeneous methodology

Evidence level: ⭐⭐ (limited, mixed results)

Tendinopathies

Several positive meta-analyses have been published on treatments for tennis elbow, Achilles tendon and other tendinopathies:

• Tennis elbow (Bjordal 2008): WMD −17.2 mm pain, +9.59 kg grip strength
• Shoulder tendinopathy (Haslerud 2014): WMD −20.41 mm VAS with monotherapy
• Achilles tendon (Tumilty 2010): −13.6 mm VAS with correct dosing

Evidence level: ⭐⭐⭐⭐ (strong, with WALT dose recommendations)

Compression/entrapment syndromes

Several meta-analyses have examined carpal tunnel syndrome:

• Significant effects on pain reduction and functional improvement
• Improved nerve conduction velocity shown in some studies
• Recommended as an adjunctive therapy alongside conservative treatments

Evidence level: ⭐⭐⭐ (moderate–strong)

Wound healing, ulcers

For diabetic foot ulcers and other hard-to-heal wounds:

• Favorable effects on time to healing
• Acceleration of wound closure shown in several studies
• Particularly promising in diabetic patients

Evidence level: ⭐⭐⭐ (moderate, further research ongoing)

Sports performance and recovery

Sports medicine is an active area of research. Lawrence and Sorra's 2024 review (PMC11503318) summarized the results:

• Positive results for preventing DOMS (delayed onset muscle soreness) – especially when applied BEFORE exercise
• Improvements in muscle performance and endurance in several studies
• Evidence for acute sports injuries is still limited
• The International Olympic Committee (IOC) is monitoring the method

Evidence level: ⭐⭐⭐ (moderate, promising)

Safety and oncological considerations

One of the most important questions is the safety of soft laser, particularly in cancer patients. Two major systematic reviews addressed this:

Zadik et al. (2019, PMID: 31109692) – management of side effects of cancer treatment:

• No evidence was found for tumor-promoting effects
• Appears safe for treating oncological side effects (mucositis, lymphedema)

Glass et al. (2023, PMC10309024) – oncologic safety of aesthetic applications:

• No clinical evidence linking PBM to tumor recurrence
• Healthy cells do not show neoplastic transformation
• In several experiments PBM reduced tumor cell viability

You can read more about soft laser contraindications in our dedicated article.

Professional guidelines and consensus

WALT (World Association for Photobiomodulation Therapy)

WALT is the leading international professional organization that:

• Publishes dosage recommendations for various indications
• Publishes standardized treatment protocols
• Sets research guidelines

Recommended wavelengths: 780–860 nm continuous laser or 904 nm pulsed laser.

2025 Delphi consensus

In 2025 the first evidence-based clinical practice guideline was published (ScienceDirect, 2025), developed by 21 international experts using the Delphi method. The 38 consensus statements' main points included:

• PBM is a safe treatment modality for adult patients
• Red-light PBM does not cause DNA damage
• Effective treatment option for peripheral neuropathy, androgenetic alopecia, and chronic wounds
• Optimal parameters are indication-dependent

The current state of research and limitations

Although soft laser therapy has a substantial body of scientific evidence, it is important to be aware of the limitations of the research:

Strengths

• Decades of research background
• Thousands of published studies
• Well-understood mechanism of action
• Favorable safety profile
• Support from international professional organizations

Limitations and challenges

• Parameter heterogeneity: Studies use different wavelengths, doses and protocols, which complicates comparisons
• Small sample sizes: Many studies have low participant numbers
• Short follow-up: Long-term efficacy is less well documented
• Publication bias: Positive results are more likely to be published
• Lack of standardization: No single treatment protocol fits all indications

What does this mean in practice?

Based on the scientific evidence, soft laser therapy:

• Is an evidence-based adjunctive therapy for several musculoskeletal and painful conditions
• Does not replace medical treatment, but can complement it
• Is most effective when applied with recommended parameters and doses
• Has a favorable safety profile – minimal side effects
• Individual response – not equally effective for everyone

Summary – Quick overview

What is this article? A comprehensive scientific review of the evidence base for soft laser (LLLT/photobiomodulation) therapy, from mechanism of action to clinical applications.

Who is it for? Anyone seeking scientifically grounded information on soft laser therapy – both laypeople and professionals.

Main message: Soft laser therapy has decades of research behind it, and for some indications strong scientific evidence supports its efficacy. However, it is not a "miracle cure" – it works best with realistic expectations and adherence to recommended protocols.

Evidence summary by indication:

• ⭐⭐⭐⭐ Strong: Knee osteoarthritis, tendinopathies, chronic neck pain
• ⭐⭐⭐ Moderate: Rheumatoid arthritis, carpal tunnel syndrome, wound healing, sports recovery
• ⭐⭐ Limited: Non-specific low back pain, some acute injuries

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Sources

1. Son Y, et al. (2025). Effects of photobiomodulation on multiple health outcomes: an umbrella review of randomized clinical trials. Systematic Reviews. PMC12326686
2. Zein R, Selting W, Hamblin MR (2018). Review of light parameters and photobiomodulation efficacy: dive into complexity. J Biomed Opt. PMC8355782
3. Stausholm MB, et al. (2019). Efficacy of low-level laser therapy on pain and disability in knee osteoarthritis. BMJ Open. PMID: 31662383
4. Glass GE, et al. (2023). Photobiomodulation: A Systematic Review of the Oncologic Safety. Aesthet Surg J. PMC10309024
5. Zadik Y, et al. (2019). Tumor safety and side effects of photobiomodulation therapy. Support Care Cancer. PMID: 31109692
6. Lawrence J, Sorra K (2024). Photobiomodulation as Medicine: LLLT for acute tissue injury. J Funct Morphol Kinesiol. PMC11503318
7. 2024 Network meta-analysis on LLLT wavelengths in KOA. Aging Clin Exp Res. PMC11455796
8. WALT (World Association for Photobiomodulation Therapy). Dosage Recommendations. waltpbm.org
9. 2025 Evidence-based consensus on clinical application of PBM. J Am Acad Dermatol. ScienceDirect
10. Immunomodulatory effects of photobiomodulation (2025). Lasers Med Sci. PMC11991943

The information in this article is for informational purposes. Interpretation of scientific evidence is continuously evolving, and individual study results may change. Home therapeutic devices are intended to complement medical treatment, not replace specialist care. Consult your physician if you have complaints.