What does science really say about soft lasers?
The story began in Budapest. In 1967, Professor Endre Mester, a surgeon, was investigating whether low-power laser light caused tumours on the skin of mice. It did not – but the illuminated animals grew their fur back faster, and their wounds also closed sooner. This chance observation launched the field of research now called photobiomodulation, which has since produced thousands of scientific publications. The field therefore has Hungarian roots – the question is what we know about it almost six decades later.
This article is not a treatment guide – you can find that in the soft laser therapy guide and in the articles about individual complaints. Here I review how strong the evidence is behind each application: where research consistently supports laser therapy, where the picture is mixed, and where there is not enough data. At the same time, you will understand how to read an individual study – because without this, numbers can be misleading.
Key point
The question “does soft laser therapy work?” cannot be answered on its own – and anyone who gives a one-word answer is oversimplifying. The right question is: for which complaint, at what dose, and according to which protocol does it work? There are already precise answers to this: in some indications (knee osteoarthritis, neck pain, tendon complaints), the evidence is strong and consistent; elsewhere it is mixed or limited. The effect proved to be dose-dependent in every study – research using the wrong dose generally found no effect.1
How is medical evidence created? The evidence pyramid
Before turning to the specific results, a short but important digression. Not every “study” is worth the same. Medicine ranks evidence according to its strength – this is usually illustrated as an evidence pyramid. If an advertisement for a device refers to a “scientifically proven” effect, the first question should always be: which level of the pyramid does the claim come from?
| Level | What is it? | How much weight does it carry? |
|---|---|---|
| Case report, expert opinion | “It worked for one of my patients” – a description of an individual experience | Useful for generating research ideas, but weak as evidence: it does not rule out chance or placebo effects |
| Study without a control group | A group of patients is treated and their improvement is measured – without comparison | Weak: most complaints improve on their own over time, and it is easy to attribute this improvement to the treatment |
| Randomised, placebo-controlled trial (RCT) | Patients are assigned by random allocation to a real-treatment or sham-treatment group – this is easy to implement with laser therapy because the sham device looks the same | Strong: filters out placebo effects and spontaneous improvement |
| Meta-analysis | Statistically combines the results of all available RCTs | Very strong: shows the overall picture using data from hundreds or thousands of patients |
| Umbrella review (“review of reviews”) | A meta-analysis of meta-analyses: evaluates the quality and results of the entire research field | The peak of the pyramid – one on soft laser therapy was published in 20251 |
What is special about soft laser research is that data now exist at every level of the pyramid – so the question is not whether there is “research”, but what the highest levels show for each indication. That is what we turn to now.
From the cell to 204 trials – the big picture
The primary target of red and near-infrared light is the enzyme cytochrome c oxidase, located in the cell’s “power plant”, the mitochondrion. This enzyme absorbs the light and works more efficiently as a result: more ATP – or cellular fuel – is produced, and a short, signalling wave of free radicals begins, switching on the cell’s repair programmes. The practical consequence is better energy supply in regenerating tissue, reduced inflammatory signalling and more active local circulation.
Important: this is not a thermal effect. Soft laser therapy does not significantly heat the tissue – the effect is photochemical, which is why the scientific literature calls it photobiomodulation: the light modulates and fine-tunes cell function; it does not burn or cut, as a surgical laser does.
The most comprehensive analysis in the field so far was published in 2025: an umbrella review evaluating 15 meta-analyses – a total of 204 randomised trials involving more than 9000 patients – across 35 outcomes in 15 disease groups.1 The result is balanced: photobiomodulation produced statistically confirmed improvement in 12 outcomes, with moderate certainty, including functional impairment caused by knee osteoarthritis, fibromyalgia-related fatigue and pain in burning mouth syndrome.
The same analysis also states that certainty is low for many outcomes – not because laser therapy has been proven ineffective, but because the study protocols differ so widely that they are difficult to combine. This duality – confirmed effects in some areas and open questions elsewhere – is the honest overall picture of the field, and this article reflects that duality too.
Most “negative” results in soft laser research can be traced back to one factor: dose. The effect of light is biphasic – a low dose switches on the cells’ repair activity, while too much inhibits it, and too little is simply absorbed without effect.2 This phenomenon (biphasic dose response) has been described repeatedly at both laboratory and clinical level.3 If a study used the wrong wavelength, too little or too much energy, it was unlikely to find an effect – and these results enter the summaries in the same way as studies using the correct dose.
This was shown most clearly in research on tendon complaints: when the meta-analysis separated the studies by dose, studies using doses consistent with international recommendations were consistently positive, while those using irregular doses were not.4 This is why the laser literature cannot be averaged indiscriminately – and why, with a home device too, it is crucial to know the dose delivered.
Evidence map: what does research show for each complaint?
The table below ranks the most important indications according to the strongest available evidence. From each row, you can go on to our detailed article about the particular complaint, where you will also find the practical protocol.
| Indication | What does the strongest research show? | Our detailed article |
|---|---|---|
| Knee osteoarthritis (cartilage wear) | Meta-analysis of 22 placebo-controlled trials: an average pain reduction of 14 mm above placebo on the 100 mm scale – nearly 19 mm in the subgroup treated with the recommended dose, with the effect peaking weeks after the course of treatment5 | Soft laser therapy for knee pain |
| Chronic neck pain | Analysis of 16 studies involving 820 patients, published in The Lancet: nearly 20 mm pain reduction compared with placebo, with the effect detectable for up to 22 weeks after treatment6 | Using soft laser therapy at home |
| Tendon complaints (tennis elbow, Achilles tendon, jumper’s knee) | Consistently positive meta-analyses using the correct dose; when added to exercise, the effects are cumulative4 – for tennis elbow, a low dose targeted at the tendon attachment point proved effective7, and the effective dose range is well defined8 | Soft laser therapy for tendonitis |
| Heel pain, plantar fascia | The meta-analysis of lower-limb tendon complaints also examined plantar fasciitis: laser therapy produced measurable pain reduction both on its own and when added to exercise4 | Soft laser therapy for heel pain |
| Carpal tunnel syndrome | Mixed picture: the 2025 meta-analysis confirmed improvement in hand function, but pain reduction did not reach statistical significance in the summary – in mild to moderate cases, it is a reasonable adjunct alongside splinting9 | Soft laser therapy for tunnel syndrome |
| Diabetic foot, difficult-to-heal wounds | Meta-analysis of 13 randomised trials: alongside laser-assisted wound care, twice as many wounds closed completely and healing time was shorter – however, the quality of evidence is low and more good-quality studies are needed10 | Treating leg ulcers with soft laser therapy |
| Sports recovery, delayed-onset muscle soreness | During post-exercise recovery, light preserved muscle strength better than cryotherapy and reduced muscle soreness – based on small studies with moderate-to-low certainty11 | Soft laser therapy for sports injuries |
| Arthritis | An adjunctive role: there is evidence for reducing pain and morning stiffness, but it does not replace treatment of the underlying disease (rheumatological drug therapy) | Soft laser therapy for arthritis |
Where is the evidence weak or incomplete? In chronic lower back pain, meta-analyses produce mixed results; for weight loss and fat reduction, “biostimulation facial rejuvenation” and many similar areas popular in marketing, there is no meaningful clinical data. If a claim does not appear in the table above, treat it with suspicion – the article on soft laser scams shows you how to recognise exaggerated claims.
Safety: what does research say about the risks?
The safety profile of soft laser therapy is consistently favourable throughout the literature: placebo-controlled studies describe, at most, mild, temporary skin redness or a temporary increase in symptoms as side effects – large meta-analyses have not recorded serious adverse effects.5 If you experience a temporary worsening of symptoms after treatment, you can read about its background in the article “why does pain worsen with treatment?”.
The most extensively studied safety question concerns oncology: could light accelerate the growth of a tumour cell that may be present? A systematic review covering 27 studies – examining photobiomodulation used for treatment-related side effects in cancer patients (mucositis, lymphoedema) – found no adverse effect on tumour behaviour.12 This does not override the need for caution: in cancer, the treating oncologist should always decide about laser treatment. I have collected the full list of contraindications – pregnancy, photosensitising medicines, eye protection and the rest – in the article on soft laser contraindications.
A favourable safety profile does not mean unrestricted use
The low risk of soft laser therapy can easily create the impression that “it cannot do any harm, so let’s try it”. The real risk is not the light – it is delay: if you treat an unexplained complaint with a home laser for weeks instead of seeking a medical diagnosis, a condition that could have been treated in time may be missed. Diagnosis first, treatment second.
My advice
If you see a “scientifically proven” effect in a device advertisement, ask the same three questions I do: does the cited study refer to the same complaint for which the device is recommended? Did it use the same type of light source and dose as the device provides? And did it include a placebo control?
If the answer to any of the three questions is no, the claim is not about that device. You can look up the studies yourself in the PubMed database – every source at the end of the article includes a clickable link, precisely for this reason.
Frequently asked questions
There may be three reasons. First, professional guidelines lag behind research by years – the results of recent meta-analyses are incorporated into everyday medical knowledge slowly. Second, many doctors know the older, mixed overall picture, which was weakened by studies using the wrong dose – analyses separated according to dose are more recent.5 Third, there is some truth in being cautious: laser therapy is not a first-line treatment, but an adjunct. Show your doctor the sources cited at the end of the article – that is exactly what they are for.
Yes, if the home device delivers the same dose – even with a longer treatment time. Most clinical studies used laser diodes with a wavelength of 780–905 nm, delivering a few joules of energy per point. A lower-power home device delivers the same energy over a longer period; what cannot be replaced is the appropriate light source and a known dose. We compared what each type of device can do in the decision guide which technology is good for what?.
An umbrella review summarises meta-analyses – it is the peak of the evidence pyramid. It can only be conducted when enough meta-analyses have accumulated in a field to make it worthwhile to organise them too. The 2025 umbrella review of soft laser therapy covered data from 204 randomised trials1 – the fact that it could be conducted indicates that photobiomodulation has now become one of the seriously researched medical methods. Its results are another matter: there is strong evidence for some indications and open questions elsewhere.
Because a single study can produce misleading results in many ways: too few patients, a favourable chance occurrence, researcher bias, or simply publication bias – positive results are easier to publish than negative ones. This is why reproducibility matters: a claim is strong when independent research groups reach similar results with placebo control, and a meta-analysis also confirms them. The phrase “confirmed by a clinical trial” used in advertisements does not meet this standard.
PubMed (pubmed.ncbi.nlm.nih.gov) is the world’s free search engine for medical literature. Enter the complaint in English together with “photobiomodulation” or “low-level laser therapy”, then select the “Meta-Analysis” and “Randomized Controlled Trial” types in the filters on the left – this will show you the upper levels of the pyramid first. Every source at the end of this article links directly to the original publication; abstracts are always freely available to read.
What the research says – answers to readers’ questions
“Is there any serious, comprehensive evidence at all, or are there only individual studies?”
There is comprehensive evidence too: the field’s highest-level analysis evaluated 15 meta-analyses – 204 randomised trials involving more than 9000 patients – across 35 outcomes. It found confirmed improvement in 12 outcomes, with moderate certainty, including functional impairment caused by knee osteoarthritis and fibromyalgia-related fatigue; in many other areas, it found low certainty and called for more consistent treatment protocols.1 This balanced picture is the benchmark – claiming more would be excessive, while acknowledging less would show a lack of knowledge.
“How do you know it is not all just a placebo effect?”
Laser trials can be blinded particularly well: the sham device looks the same and feels the same – that is, it cannot be felt – as the real one, so the patient does not know which they receive. In knee osteoarthritis, a summary of 22 such placebo-controlled trials showed that real laser therapy reduced pain by an average of 14 mm more than placebo – nearly 19 mm more in the recommended-dose subgroup, with the difference greatest 2–4 weeks after the course of treatment.5 A placebo cannot produce a dose-dependent effect curve that develops in this way over time.
“Is there evidence for my neck too, or only for knees?”
Neck pain is one of the strongest areas of laser research – the analysis was published in the medical journal The Lancet. Data from 16 randomised trials involving 820 patients showed that laser treatment reduced pain in chronic neck pain by nearly 20 units compared with placebo on the 100-point scale, and the effect remained detectable 1–22 weeks after the treatment series. Side effects were mild and did not differ from those in the placebo group.6
Summary
What is this article about? A review of the scientific evidence for soft laser therapy: from the evidence pyramid through the 2025 umbrella review to the indication-specific evidence map – with a clickable source behind every claim.
Who is it for? Anyone who wants to know what is and is not supported by evidence before buying or undergoing treatment – and healthcare professionals looking for a reliable starting point when answering their patients’ questions.
Main message: Soft laser therapy is neither a miracle cure nor a placebo – it is a dose-dependent medical method with strong evidence for some indications (knee osteoarthritis, neck pain and tendon complaints), and mixed or incomplete evidence elsewhere. The right question is never whether it “works”, but what research shows for your complaint when the correct dose is used.
Next step: Find your complaint on the evidence map and continue to the detailed article – you will also find the practical protocol there. Before choosing a device, read the checklist for avoiding scams too.
Read more
- Soft laser therapy guide: how it works, dose and laser classes
- Soft laser therapy at home: how should you use it for each complaint?
- Which technology is good for what? A decision guide
- Soft laser scams: how to recognise exaggerated promises
- Soft laser contraindications: when should you not use it?
- Soft laser therapy for knee pain: what can you realistically expect?
- Soft laser therapy for tendonitis: protocol and load management
If you want to choose a device based on the research
Translated into device selection, the lesson from the studies above is: a laser diode with a known wavelength, a documented dose and CE-marked medical-device certification. Three such devices:
B-Cure Laser Pro
A Class 1 pulsed device with a large treatment surface – safe to use at home without protective goggles. Convenient for treating larger body areas (knee, neck and shoulder region); it offsets its lower power with a longer treatment time.
Personal-Laser L400
A 400 mW, 808 nm diode laser – it operates in the infrared range most commonly used in clinical studies, so the dose per point can be delivered in a short time. A practical choice for localised complaints (tendon attachment points, small joints).
Energy-Laser L500 Pro
A 500 mW professional home device with built-in, complaint-specific programmes – the device controls the dosing, so the energy doses used in research can be reproduced predictably.
You can find the full range in the soft laser device category – before buying, it is worth reviewing the scam-avoidance checklist.
Scientific sources
- Son Y, Lee H, Yu S, et al. (2025). Effects of photobiomodulation on multiple health outcomes: an umbrella review of randomized clinical trials. Systematic Reviews. DOI: 10.1186/s13643-025-02902-3
- Huang YY, Chen ACH, Carroll JD, Hamblin MR. (2009). Biphasic dose response in low level light therapy. Dose-Response. DOI: 10.2203/dose-response.09-027.Hamblin
- Zein R, Selting W, Hamblin MR. (2018). Review of light parameters and photobiomodulation efficacy: dive into complexity. Journal of Biomedical Optics. DOI: 10.1117/1.JBO.23.12.120901
- Naterstad IF, Joensen J, Bjordal JM, et al. (2022). Efficacy of low-level laser therapy in patients with lower extremity tendinopathy or plantar fasciitis: systematic review and meta-analysis of randomised controlled trials. BMJ Open. DOI: 10.1136/bmjopen-2021-059479
- Stausholm MB, Naterstad IF, Joensen J, et al. (2019). Efficacy of low-level laser therapy on pain and disability in knee osteoarthritis: systematic review and meta-analysis of randomised placebo-controlled trials. BMJ Open. DOI: 10.1136/bmjopen-2019-031142
- Chow RT, Johnson MI, Lopes-Martins RA, Bjordal JM. (2009). Efficacy of low-level laser therapy in the management of neck pain: a systematic review and meta-analysis of randomised placebo or active-treatment controlled trials. The Lancet. DOI: 10.1016/S0140-6736(09)61522-1
- Bjordal JM, Lopes-Martins RA, Joensen J, et al. (2008). A systematic review with procedural assessments and meta-analysis of low level laser therapy in lateral elbow tendinopathy (tennis elbow). BMC Musculoskeletal Disorders. DOI: 10.1186/1471-2474-9-75
- Tumilty S, Munn J, McDonough S, et al. (2010). Low level laser treatment of tendinopathy: a systematic review with meta-analysis. Photomedicine and Laser Surgery. DOI: 10.1089/pho.2008.2470
- Lauxen AC, Machado DR, Pereira DS, et al. (2025). Photobiomodulation in carpal tunnel syndrome with pain, strength, and functionality analysis: a systematic review and meta-analysis. Lasers in Medical Science. DOI: 10.1007/s10103-024-04276-9
- Huang J, Chen J, Xiong S, et al. (2021). The effect of low-level laser therapy on diabetic foot ulcers: a meta-analysis of randomised controlled trials. International Wound Journal. DOI: 10.1111/iwj.13577
- Ferlito JV, Ferlito MV, Leal-Junior ECP, et al. (2021). Comparison between cryotherapy and photobiomodulation in muscle recovery: a systematic review and meta-analysis. Lasers in Medical Science. DOI: 10.1007/s10103-021-03442-7
- de Pauli Paglioni M, Araújo ALD, Arboleda LPA, et al. (2019). Tumor safety and side effects of photobiomodulation therapy used for prevention and management of cancer treatment toxicities. A systematic review. Oral Oncology. DOI: 10.1016/j.oraloncology.2019.04.004
