A laser shining through a cloud of particles.
Photobiomodulation therapy (PBMT) is the use of light as a medical treatment. “Cold” or low-level laser therapy (LLLT) is the best-known specific type of PBMT, but it’s not a great term, just a customary one.1 Laser light is only one of many riffs on the photobiomodulation tune. For instance, even tanning beds could be considered one form of PBMT (to stimulate vitamin D production), and far infrared saunas are advertised like they beam healing heat rays.2
But I will speak mostly of “lasers” in this article, because it’s fun and half-right. 🙂
Lasers seem to attract cranks and quacks, and laser therapy is strongly associated with much more than its fair share of bullshit and fraud. Skeptical appraisals of laser therapy are harsh.3 According to the people selling cold laser treatments, there’s almost no limit to the conditions that will benefit from laser therapy, and the internet is awash with images like this:
A “chart” showing the conditions laser therapy is supposedly good for, which apparently is basically anything you can name, including several that are notoriously impossible to treat.
The big idea is that lasers can supposedly stimulate healing (as opposed to, you know, burning a hole in you like a starship trooper). They are intended to help damaged tissue recover faster, or finish recovering when it’s struggling to. It is not just a pain treatment, and it’s not about heating tissues at all (one reason it’s often called “cold” laser therapy).4 If it works, it’s a big deal.
It would be such a big deal that one might ask: where is the Nobel prize for that?5 I’ve been doing this job long enough to know that, if a treatment was genuinely promising and legit, I probably would’ve heard about it long ago. The WHAILO principle!6 I appreciate that legitimately interesting medicine can cruise along in obscurity for a long-time for many reasons, but the effects claimed for lasers are truly amazing. These are perfect examples of the “extraordinary claims” that Sagan famously said require “extraordinary evidence.”
With all such treatments, one can always claim that there’s hope that they will work miracles with the right settings for the right patients — adjust the dials the right way and amazing things will happen — but no one ever seems to be able to confirm what the right settings are and who the right patients are. Once in a blue moon something pans out, but most never do, or they fail to be useful even when there’s genuinely promising basic biological effects involved.8
Actually, it’s hard to think of an example of any technological therapy that has panned out.
But laser therapy has its fans, of course! And its inevitable “promising” evidence of dubious value.
One simply cannot speak of lasers without this pop culture reference.
The not-actually-promising evidence
An educated reader brought this paper to my attention, hoping to persuade me to take laser therapy seriously. In 2014, Alves et al published a glowing review of 17 papers about LLT specifically for the “short-term” treatment of muscle injuries.9 They found that it reduced inflammation, and stimulated the growth of new blood vessels, and improved muscle recovery. They called it an “excellent therapeutic resource for the treatment of skeletal muscle injuries.” This sounds very good. And does indeed appear to be the best scientific review of this topic to date.
There’s a catch, though. Seems like there always is.
Animals only! They were only reviewing animal studies, because animal studies are the only studies to review. As of 2018, there is still not even one human trial (for muscle strain specifically). Obviously animal studies are not adequate. What works on other animals routinely fails with human animals and vice versa.
There is basically just no persuasive clinical science on this topic. There is (of course) lots of low-quality evidence showing mixed and trivial effects10 — that’s just standard these days. The lack of quality evidence does not mean it doesn’t work, but it does damn laser therapy with faint praise and highlight a suspicious failure so far to produce better evidence. And it means that laser therapy cannot yet be considered evidence-based — it can only be hope-based. All we can do is try to rationally evaluate the plausibility, costs, and risks.
At least, there was no persuasive evidence until 2021…
Real laser therapy no better than a lower-power red LED for back pain
In 2021, something surprising happened: a new, high-quality trial was published in the journal Pain.11 A properly good study (with humans). In a good journal. I believe it is the first of its kind.
The placebo used in this trial was particularly ideal. And a bit amusing.
Guimarães et al compared laser therapy to a premium placebo in 148 Brazilians with chronic unexplained low back pain. Pain and disability were tracked for a year, plus some other secondary measures. Patients got a dozen treatments over a month. Half received real laser therapy, and the other half got… some tame red light!
The sham device was the same device as the real one, just with the business end disabled, not emitting a therapeutic dose — just one low-powered red light. Laser therapy doesn’t feel like anything, so there was simply no way for patients to know whether they were getting real lasers or not.12
The illuminating results
So what happened?! What any reasonably savvy cynic would expect: there was no important difference between real laser therapy and the fake stuff.
More specifically, there was no clinically important difference in pain intensity, general disability, or any secondary outcome after one, three, six, or twelve months.13
Although this is “just one study,” it’s a good one, and this is a rare case when I think the quality and credibility of the journal is particularly noteworthy. Most studies of laser therapy have been published in obscure and junky little journals. This one really stands out… and, as I hoped it might, the trial itself really ticks all the right boxes. Unlike so many studies in this field, it was designed to actually answer the question — big enough and good enough. Nothing’s perfect, but this one has a lot going for it.14
This isn’t the last word in laser research, of course
As always with laser therapy, it’s quite reasonable to wonder if fiddling with the dials might make an important difference, and the authors — who have some vested interests in laser therapy — urge further investigation of “the optimization of PBMT parameters.” And it’s hard to disagree with that.
But the counter-argument is simple: they used lasers the WALT way, using frequencies and intensities recommended by the World Association of PhotobiomoduLation Therapy.
What if the WALT way is the wrong way? That’s a huge problem for laser therapy. When the officially endorsed method is utterly ineffective, what are the odds that some other way is going to work well? Or at all? Even if a different dosage is eventually proven effective, that would also mean that the experts at WALT got it hopelessly wrong up to that point… and laser therapy as we know it today is based on guessing, not evidence.
Which is, in fact, precisely the case.
WALT’s mission? “To stimulate high quality research in photobiomodulation…” They got that in this case — arguably for the first time. Be careful what you wish for, WALT!
The stock image services are choked with photos like this one from Shutterstock — they are there to promote products & treatment methods.
How likely is it that lasers stimulate healing? In humans?
There is a clear biological response of human skin to UV radiation: it makes vitamin D, which is quite important to us. This is the main template for all other ideas photobiomodulation. A few other biological effects of light have been confirmed over the decades, like its role in regulating circadian rhythms. There are photosensitive proteins. Light does affect biology.15
So what else might light do to us? What about radiation on different parts of the EM spectrum? What about “coherent” (laser) light?
Could light … heal? Could lasers? It’s not clear why anyone would suspect that specifically based on what is known about the effects of light. I think it’s a nearly perfect unknown. I am not aware of any specific reason to think that laser can facilitate healing.
But I can think of a reason why it wouldn’t. The hopes of all kinds of regenerative medicine are all pinned on the grand idea that biology has potential for improved healing that can be “unlocked.” But this is broadly implausible. Biology doesn’t really have many valuable hidden features that only emerge with an exotic/rare stimulus: either a system didn’t evolve in the first place, or it did and we’re already using it.
But biology is also insanely complex, so who knows?
This is just one of those things that we’ll simply have to test — more thoroughly and much better than we have so far.
Lasers versus LEDs
PBMT is about using light as therapy, but not all PBMT uses lasers. Many PBMT devices are actually using LEDs, or a mixture. Lasers are more expensive and, of course, allegedly better. Laser light has some unique properties such as monochromaticity, coherence, collimation or polarization — and, of course, laser therapy proponents have always argued, often vehemently, that lasers are better.
Indeed, it’s almost a cliché of PBMT crankery to be overheated about lasers. “Coherence,” especially, is almost fetishized by the laser lovers.
But it is not clear that lasers are inherently superior for PBMT. “According to current knowledge, this is certainly debatable and probably not true,” write Heiskanen et al. That’s from their review that is extremely bullish about PBMT in general… and yet they conclude that the evidence so far shows that “photobiomodulation is not dependent on lasers or coherence.”16 They acknowledge that the evidence is limited, and that it’s an ongoing controversy, but it’s pretty hard for someone without a dog in this fight to read that review without thinking the difference cannot possibly matter much, if at all.
And keep in mind that no clear clinical utility of any kind of PBMT has yet been demonstrated, so the whole lasers versus LED thing is a bit of a tempest in a teapot. Wake me up when either of them show actual promise in a clinical trial.
Laser therapy costs
Costs of laser therapy gadgets for home use range widely, but tend to be higher than other related gadgets (TENS, PEMF, ultrasound, etc). A typical one is well over a hundred bucks. Anyone selling laser therapy in a clinic is likely to heap scorn on the DYI approach, because they like you to pay them by the session. As with all such services, repeated applications and package “deals” are the normal, and the total price tag is non-trivial: probably less than massage, but with virtually no potential side benefits.
Laser therapy risks
Lasers certainly can be dangerous if used improperly. Obviously. •pew pew!•
In practice, commercially available PBMT gadgets are mostly working with such low energies that the risk is probably very low even if used improperly. On the other hand, there are many products with widely ranging features … and some really sketchy people selling laser therapy. I have no hard safety data, but with so many devices and so many sketchy providers, there is probably some risk.
Here be cranks!
Like “quantum” and “toxins,” lasers sound cool. They are a great marketing tool. The way laser therapy is advertised and used in the wild does raise a lot of red flags and makes it a lot harder to separate sense and nonsense.
For instance, consider the claim that laser therapy for trigger points works because it “energizes the damaged cells.” That was stated by someone who trains trigger point therapists. It’s really crazy, but it’s a common claim made by laser therapy mongers. It’s not even defensible as an informal, dumbed down explanation of anything, because there’s no more complicated version to simplify. It’s just pure nonsense that has nothing to do with actual biology, a classic example of “not even wrong.” It’s so ridiculous that I wouldn’t even bring it up if it weren’t actually representative of laser therapy claims. And it’s not even the worst!
An even more ridiculous laser therapy claim reported by someone else: it “kickstarts photosynthesis in human cells”! That’s not even close to an actual thing, of course, because humans aren’t plants and we don’t do photosynthesis, ever.
When people are talking like this about laser therapy, it’s a lot harder to take it seriously.
Laser therapy has a nasty frickin’ theory versus practice problem:
- Theory: There’s some legitimately intriguing basic science observations about the effects of light/lasers on biology, and in a perfect world these effects would be investigated systematically and rationally over many years and, someday, they might lead somewhere clinically useful.
- Practice: Laser therapy is embraced and sold almost exclusively by the ignorant and profiteering, none of whom really have a clue if they are using the right kind of lasers in the right way on the right tissues, and if there’s any real healing effect it’s probably only happening by fluke in a few cases.
In the real world, I don’t think laser therapy reaches the threshold required for being “worth a shot” — not even if you’re desperate, not even if you can easily afford it. Although safe and plausible in an anything’s-possible way, it’s just too much of a long shot to be worth a shot. By far the most likely result is that you simply waste your time and transfer some of your wealth to someone who doesn’t deserve it.
About Paul Ingraham
I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of ScienceBasedMedicine.org for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter., or subscribe:
- Salamander and Regeneration Science — Why does PainScience.com have a salamander mascot? Their regenerative superpower is an inspiring, profound example of what is possible in biology and healing
- Does Platelet-Rich Plasma Injection Work? — An interesting treatment idea for arthritis, tendinopathy, muscle strain and more
- Does Cartilage Regeneration Work? — A review of knee cartilage “patching” with autologous chondrocyte implantation (ACI)
- Zapped! Does TENS work for pain? — The peculiar popularity of being gently zapped with electrical stimulation therapy
- Does Ultrasound Therapy Work? — Many concerns about the widespread usage of therapeutic ultrasound, especially extracorporeal shockwave therapy (ESWT)
- Heat for Pain and Rehab — A detailed guide to using heat as therapy for acute and chronic pain and recovery from injury. The discussion of infrared radiation particularly relevant.
What’s new in this article?
2021 — Added a small new section, “Lasers versus LEDs,” explaining one of the hottest ongoing controversies about photobiomodulation therapy (and much ado about not much).
2021 — Added detailed analysis of a major new trial of laser therapy for back pain.
2018 — Added footnote about new Nobel prizes for laser technology, and how it has already been exploited to sell cold laser therapy.
2018 — Publication.
- Anders JJ, Lanzafame RJ, Arany PR. Low-level light/laser therapy versus photobiomodulation therapy. Photomed Laser Surg. 2015 Apr;33(4):183–4. PubMed 25844681 ❐ PainSci Bibliography 53021 ❐ “In addition to biostimulation, a few of the other names previously used for this therapy have included low-level laser (or light) therapy (LLLT), low-intensity laser therapy, low-power laser therapy, cold laser, soft laser, photobiostimulation, and photobiomodulation.”
- Infrared radiation is basically synonymous with “heat.” far infrared radiation is the part of the infrared section of the electromagnetic spectrum with the longest wavelengths, and it is widely touted to penetrate at least a few centimetres into tissue; the citation usually given for this (if any) does not actually support the claim. Effects on biology beyond simply warming tissues are conceivable, but have never actually been documented. I explore this topic in more detail in my thermotherapy article: Heat for Pain and Rehab: A detailed guide to using heat as therapy for acute and chronic pain and recovery from injury.
- www.devicewatch.org [Internet]. Barrett S. A Skeptical Look at Low Level Laser Therapy; 2018 Apr 26 [cited 18 Sep 24]. PainSci Bibliography 52995 ❐
- Anders JJ, Lanzafame RJ, Arany PR. Low-level light/laser therapy versus photobiomodulation therapy. Photomed Laser Surg. 2015 Apr;33(4):183–4. PubMed 25844681 ❐ PainSci Bibliography 53021 ❐ “The use of this term is key, as it distinguishes photobiomodulation therapy, which is nonthermal, from the popular use of light-based devices for simple heating of tissues as can be accomplished using near-infrared (NIR) lamps, or other applications of light energy that rely on thermal effects for all or part of their mechanism of action.”
- Multiple Nobel prizes have been awarded for the medical uses of lasers — see the Ashkin, Mourou, Strickland 2018 prizes for “optical tweezers” and short and intense laser bursts with many medical applications. These are not prizes for photobiomodulation. But that didn’t stop one cold laser therapy brand from strongly implying with a Facebook post that these Nobel prizes were relevant. To be fair, they didn’t actually say it was the same kind of laser application, and the post could easily be interpreted as general enthusiasm for laser technology. But, shocker, they didn’t go out of their way to explain that the Nobel prizes were awarded for completely different technology than cold laser therapy. 😜 Obviously this news is going to be exploited to help sell cold laser therapy.
- Which should be getting more potent as I age. Another decade of this and I won’t have to critically evaluate any claim!
“Mechanism masturbation” is wishful and fanciful thinking about why/how treatments might work. Science journalist Jonathan Jarry:
“There is a fascinating phenomenon in the complementary and alternative medicine literature we could call ‘mechanism masturbation’ where the authors, faced with the tiniest of positive signals in a small study, write paragraph after paragraph hypothesizing how, mechanistically, watermelon seeds might cure schizophrenia.”
Musculoskeletal and pain research, alternative as well as more mainstream research, is rotten with “mechanism masturbation” — often because it’s just all there is. There’s no good clinical trial data, so we get wishful thinking and wild speculation instead, even in scientific publications. The field is surprisingly afflicted with with cart-before-horse speculation about how they how they could work, might work, should work, maybe work… when the clinical trials (if they exist at all) tend to show that they don’t actually work, or not very well.
Jonathan’s satirical example really nails the flavour of “research” like this:
“It might interfere with the hypothalamic-pituitary-adrenal axis… One of its compounds does bind to alpha receptors in this cell type… Could play a role in this cascade... Anyway, preliminary results from n = 6. More studies needed!”
Yes, that definitely reads like about a thousand papers I’ve wasted my time reading over the last decade. I’m always looking for the rare scraps of basic science I can actually consider interesting/promising instead of more post-hoc rationalization for someone’s meal ticket. 🙄
- For example, tanning beds really do stimulate vitamin D production — a genuine, interesting, useful biological effect of shining light on people — but there’s a list of practical problems that makes using them a really terrible idea. And those problems have only become clear after decades of the technology being widely used! See Woo and or my vitamin D article for much more information.
- Alves AN, Fernandes KPS, Deana AM, Bussadori SK, Mesquita-Ferrari RA. Effects of low-level laser therapy on skeletal muscle repair: a systematic review. Am J Phys Med Rehabil. 2014 Dec;93(12):1073–85. PubMed 25122099 ❐
- Crislip, Mark. Low Level Lasers: N-Rays in action. ScienceBasedMedicine.org. August 24, 2012. “Like acupuncture, there is a huge literature (4000 on the Pubmeds) of mostly poorly done studies, some showing effect, some not. The Cochrane reviews were not supportive of laser therapy, but note the studies are uniformly lousy.”
- Guimarães LdS, Costa LdC, Araujo AC, et al. Photobiomodulation therapy is not better than placebo in patients with chronic nonspecific low back pain: a randomised placebo-controlled trial. Pain. 2021 06;162(6):1612–1620. PubMed 33449509 ❐ PainSci Bibliography 52147 ❐
The quality of the placebo is so important to this study that I’ll quote their description in full:
In the PBMT device used, the only visible diode is the red one. For the placebo treatment, 905 nm laser diodes and the 875 nm LED diodes were deactivated (turned off), and the power of the 640-nm LED diodes were turned down to 1 mW (mean power for each diode) to keep the visual aspect of red light, but not to deliver an effective therapeutic or considerable dose according the current available evidence.
(Funny that the authors felt it was necessary to clarify “deactivated” with the parenthetical “turned off.” Of all the jargon in this paper, that was the term that needed definition?)
- Yes yes yes, there was a slight boost in “global perceived effects” at one month for the lasered folks. Laser therapy advocates will point to this single data point and declare victory. But it’s just a moderate, temporary, short-term benefit for a rather squishy secondary way of measuring the effect of therapy — and it’s entirely possible it would vanish if you did the whole study all over again.
- One good example of the quality of the trial is that, delightfully, it was “prospectively registered” — which means that they declared in advance what they were up to (which makes it harder to fudge things later; p-hacking is harder when you’ve put all your cards on the table in advance).
- Editors. The light fantastic. Nat Chem Biol. 2014 Jul;10(7):483. PubMed 24937055 ❐ PainSci Bibliography 52994 ❐
- Heiskanen V, Hamblin MR. Photobiomodulation: lasers vs. light emitting diodes? Photochem Photobiol Sci. 2018 Aug;17(8):1003–1017. PubMed 30044464 ❐ PainSci Bibliography 52101 ❐
From the conclusion:
The current total evidence appears to support the idea that photobiomodulation is not dependent on lasers or coherence, but quasimonochromatic LED devices and even broad-wavelength light sources such as water-filtered infrared-A can also yield physiological effects. The comparisons between lasers and LEDs lend support to this idea. However, the quality of these comparisons is low for the most part, because of the difficulty of arranging the parameters so that the beam from a LED is identical to the beam from a laser, with regard to spot-size, band-width and power density. Nevertheless, even today the debate about the equivalence of laser and LED remains the single most controversial topic in the PBM field.