Low-level laser therapy

Based on Wikipedia: Low-level laser therapy

In 1967, a Hungarian scientist named Endre Mester made one of medicine's more amusing accidental discoveries. He was trying to zap tumors in mice with a ruby laser—replicating an experiment that had shown promising cancer-fighting results. But his laser was broken. It was far weaker than he thought.

The tumors didn't shrink. The experiment was a failure.

Except Mester noticed something strange. He had shaved the mice to expose the tumors, and now their fur was growing back faster than normal. Much faster than the control group. His malfunctioning equipment had stumbled onto something entirely unexpected: low-power light could stimulate biological processes.

This happy accident launched a field now known by several names—low-level laser therapy, cold laser therapy, or the more technical term that professionals prefer: photobiomodulation. The "photo" refers to light, "bio" to living things, and "modulation" to changing or adjusting. In plain terms: using light to influence how cells behave.

The Science of Shining Light on Skin

Here's the fundamental principle at work, and it comes from one of the first laws of photochemistry, discovered back in the early 1800s by scientists named Grotthuss and Draper. Light must be absorbed by something to have any chemical effect. You can shine a flashlight through a window all day, but the glass doesn't change because it doesn't absorb those wavelengths—the light passes right through.

In photobiomodulation, the "something" that absorbs the light is a molecule called cytochrome c oxidase. This is an enzyme—a biological catalyst—that lives inside your mitochondria. You might remember mitochondria from biology class as "the powerhouse of the cell." That's because mitochondria produce adenosine triphosphate, or ATP, which is essentially the energy currency that powers nearly everything your cells do.

Cytochrome c oxidase is part of the electron transport chain, a series of molecular machines inside mitochondria that create ATP. When certain wavelengths of red or near-infrared light hit this enzyme, it appears to work more efficiently. More efficient mitochondria means more cellular energy. More cellular energy means cells can do their jobs better—whether that's healing a wound, reducing inflammation, or, apparently, growing hair on mice.

But here's the catch: the dose matters enormously. Too little light, and nothing happens. Too much light, and you can actually harm cells by generating what chemists call "singlet oxygen"—a reactive form of oxygen that damages biological molecules. There's a Goldilocks zone, and finding it has been one of the central challenges of the field.

A Bewildering Array of Names

If you've tried to research this topic, you've probably encountered a confusing alphabet soup of terminology. Low-level laser therapy. LLLT. Cold laser therapy. Red light therapy. Photobiomodulation. Low-power laser irradiation. Soft laser therapy. Bio-stimulation laser therapy. Photo-biotherapy. Therapeutic laser. Monochromatic infrared light energy therapy, sometimes abbreviated as MIRE.

They're all referring to essentially the same thing.

The proliferation of names happened partly because the field developed simultaneously in different countries, partly because marketers kept inventing new terms, and partly because scientists themselves couldn't agree on what to call it. The confusion around "low level" was particularly problematic—low compared to what? Surgical lasers that can cut tissue? The sun?

When practitioners started using light-emitting diodes (LEDs) instead of lasers, the "laser" in the name became technically inaccurate for many devices. This pushed the field toward "photobiomodulation" as the preferred umbrella term. It's more precise, if less catchy.

When the therapy targets specific applications, even more names emerge. Shine it on acupuncture points? That's laser acupuncture. Direct it at the head through the skull? Transcranial photobiomodulation, or transcranial low-level light therapy.

What Red Light Therapy Claims to Treat

The list of conditions that photobiomodulation has been promoted for is staggeringly long. Musculoskeletal problems like carpal tunnel syndrome, fibromyalgia, osteoarthritis, rheumatoid arthritis, and chronic back pain. Skin conditions and wound healing. Dental problems including gum disease and tooth sensitivity. Hair loss. Brain injuries. Even smoking cessation and tuberculosis.

Some of these claims have reasonable scientific support. Others are speculative at best. And some have landed device manufacturers in serious legal trouble.

In 2014, the United States Food and Drug Administration went after a company called QLaser, alleging that they were marketing their devices as treatments for "over 200 different diseases and disorders"—including cancer, cardiac arrest, deafness, diabetes, HIV/AIDS, and venereal disease. The case resulted in a permanent injunction in 2015. Then, in 2017, the company's owner and two distributors faced criminal conspiracy charges. The owner, Robert Lytle, pleaded guilty to fraud and contempt charges and was sentenced to twelve years in prison, with an initial restitution payment of over six hundred thousand dollars.

This case illustrates the gap between legitimate research into photobiomodulation and the wild claims that sometimes surround it. Just because a therapy shows promise for one condition doesn't mean it works for everything.

What Actually Works (Probably)

Let's look at where the evidence is strongest.

Oral mucositis is inflammation and ulceration in the mouth—painful sores that often develop as a side effect of chemotherapy, particularly in people receiving stem cell transplants. Multiple studies have found that photobiomodulation can help prevent these sores from forming. The evidence is strong enough that major insurance companies like Blue Cross Blue Shield and Aetna actually cover the treatment for this specific purpose—though notably, they don't cover it for anything else.

The therapy also shows promise for juvenile myopia (nearsightedness in children) and rheumatoid arthritis, though the evidence is still being investigated.

For hair loss, the picture is interesting. Remember Mester's mice? Researchers have continued exploring this application for decades. A 2017 review examined eleven clinical trials and found that ten of them showed significant improvement in androgenetic alopecia—the medical term for common pattern baldness—compared to controls. The devices come in various forms: combs, hats, helmets. The type of device doesn't seem to matter much, but lasers appear more effective than LEDs.

Different types of hair loss respond to different wavelengths. Alopecia areata, an autoimmune condition where hair falls out in patches, seems to respond better to ultraviolet and infrared light. Androgenetic alopecia responds better to red and infrared light.

Some medical reviews suggest photobiomodulation might be as effective as, or potentially more effective than, traditional hair loss treatments like minoxidil (the active ingredient in Rogaine) and finasteride (sold as Propecia). But the research community emphasizes that larger, better-designed studies are still needed.

What Probably Doesn't Work (Or We Don't Know Yet)

For chronic low back pain—one of the most common reasons people seek medical treatment worldwide—the evidence is decidedly mixed. A 2008 Cochrane review (Cochrane reviews are considered the gold standard for evaluating medical evidence) found insufficient support for using the therapy. A 2010 review agreed. Then a 2015 review found benefits for nonspecific chronic low-back pain. The contradictory findings suggest either that the treatment has modest effects that are hard to detect, or that study quality varies so much that we can't draw firm conclusions.

Neck pain shows a similar pattern. Some studies find benefits, but a 2013 systematic review concluded that any benefits weren't clinically significant, and the evidence had a high risk of bias—meaning the studies might have been designed or conducted in ways that made the treatment look better than it actually is.

For temporomandibular joint disorders—problems with the jaw joint that can cause pain, clicking, and difficulty chewing—photobiomodulation doesn't appear to reduce pain, though it might improve function.

For muscle soreness after exercise, the evidence doesn't support any benefit.

The Depth Problem

One of the fundamental challenges with photobiomodulation, especially when applied to the brain, is penetration depth. Light doesn't travel through tissue the way it travels through air.

Think about holding a flashlight against your palm in a dark room. You can see a reddish glow, but the light is dramatically diminished. It's being absorbed and scattered by your skin, blood, and tissue.

The numbers are sobering. White light and LED radiation can only penetrate between 0.0017 millimeters and 5 millimeters of tissue—and that upper range is optimistic. At wavelengths of 450 nanometers (blue light) and 650 nanometers (red light), only about one percent of the light reaches a depth of approximately 1.6 millimeters. Almost nothing reaches 5 millimeters.

This creates real problems for transcranial photobiomodulation—attempts to treat the brain by shining light through the skull. The human skull is typically six to seven millimeters thick, and then there's the brain tissue itself. If only lasers (not LEDs) can penetrate deeper tissues, and even then the penetration is limited, how much light actually reaches the brain structures that might benefit?

Researchers are still grappling with these questions. The connections between neuronal activity and mental processes remain active areas of investigation. Whether transcranial photobiomodulation can actually reach the specific brain regions that would benefit from treatment is genuinely unclear.

From Hungary to Your Medicine Cabinet

The story of how this therapy spread around the world traces back to Mester's continued work after his accidental discovery. Through the 1970s, he applied low-level laser light to treat people with skin ulcers. In 1974, he founded the Laser Research Center at Semmelweis Medical University in Budapest, where he worked until his death in 1984.

His sons carried on the research and eventually brought it to the United States. By 1987, companies were already making ambitious claims—that their lasers could treat pain, accelerate healing of sports injuries, and help with arthritis. The evidence at that time was thin, but the marketing was enthusiastic.

The field owes an even earlier debt to Niels Finsen, a Faroese physician working in the late 1800s. Finsen is considered the father of modern light therapy. He used red light to treat smallpox lesions and won the Nobel Prize in Physiology or Medicine in 1903 for his work on light therapy for lupus vulgaris, a form of skin tuberculosis.

Interestingly, much of Finsen's specific work has been rendered obsolete. The eradication of smallpox and the development of antibiotics for tuberculosis meant that light therapy was no longer needed for those conditions. But the broader principle—that specific wavelengths of light can affect biological processes—lived on and eventually found new applications.

Safety and Side Effects

Compared to many medical interventions, photobiomodulation appears relatively safe. The most commonly reported side effects are mild: some pain or skin irritation after treatment.

But there are important caveats.

We don't know the long-term effects on skin or hair from repeated treatments. Eye protection is recommended for some devices—you don't want to shine lasers into your eyes. And importantly, different skin types respond differently. The biological effects of various wavelengths can vary depending on a person's skin type, race, and ethnicity. Clinical guidelines suggest consulting a dermatologist before undergoing treatment.

For people with cancer or at risk of cancer, a systematic review found no evidence that they need to avoid photobiomodulation. This is reassuring, since one might worry that stimulating cell growth could be dangerous for people with cancer. The current evidence suggests this isn't a concern, though it's an area that continues to be studied.

If you're considering trying red light therapy at home, experts recommend using only devices that have been approved for use on humans by your country's regulatory authority. In the United States, that means FDA-cleared devices specifically approved for dermatologic application. The market is flooded with products making dubious claims, and regulatory oversight varies widely.

The Insurance Reality

How insurance companies treat a therapy tells you something about how the medical establishment views it.

Blue Cross Blue Shield and Aetna cover photobiomodulation for one thing only: preventing oral mucositis. That's it. Not pain, not wound healing, not hair loss, not any of the dozens of other promoted uses.

The Centers for Medicare and Medicaid Services—the federal agency that administers Medicare, the health insurance program for Americans over 65—doesn't cover low-level laser therapy at all.

Cigna, another major insurer, lists it as "experimental, investigational, or unproven for any indication" and provides literature review summaries for various conditions—a polite way of saying they've looked at the evidence and aren't convinced.

This conservative stance reflects the current state of the science: promising for a few conditions, unclear for many others, and definitely not ready for routine clinical use across the board.

The Veterinary Connection

Veterinary clinics have embraced cold laser therapy, using devices to treat everything from arthritis to wounds in dogs and cats. Walk into many animal hospitals today, and you'll find laser equipment available.

But the evidence base for veterinary use is even thinner than for humans. Brennen McKenzie, president of the Evidence-Based Veterinary Medicine Association, has been blunt about this: "Research into cold laser in dogs and cats is sparse and generally low quality. Most studies are small and have minimal or uncertain controls for bias and error."

He acknowledges that some studies show promising results, but concludes that the evidence isn't sufficient to support routine clinical use. Pets can't tell us if they feel better or if the treatment helped, which makes studying these interventions even more challenging.

The Difference Between Lasers and LEDs

When Mester made his discovery, he was using a laser—specifically, a ruby laser. Lasers produce coherent light: all the photons have the same wavelength and travel in the same direction, in phase with each other. This is why laser pointers create that distinctive narrow beam.

Light-emitting diodes produce incoherent light: the photons have the same wavelength but aren't perfectly aligned or in phase. LED light spreads out more, like a flashlight.

Does this difference matter for biological effects? It's an ongoing debate. Some researchers argue that laser light's ability to penetrate deeper into tissue makes it superior. Others suggest that for many applications, especially those targeting surface tissues, LEDs work just as well and are cheaper and safer.

The studies comparing lasers to LEDs directly are limited, and the field hasn't reached consensus. This uncertainty extends to many aspects of photobiomodulation: What wavelengths work best? How much power? How long should each session last? How large an area should be treated?

These parameters matter enormously—below a certain dose, nothing happens; above another threshold, you risk harm—but the clinical trials comparing different approaches are insufficient to provide clear guidance.

Emerging Applications

Research continues to explore new uses for photobiomodulation.

For breast cancer-related lymphedema—swelling caused by damage to the lymphatic system, often from cancer surgery or radiation—a 2015 systematic review found "moderate-strength evidence" supporting the therapy. Patients showed reductions in both the volume of affected tissues and in pain immediately after treatment.

Scientists are also investigating whether the therapy could help with traumatic brain injury and stroke recovery, though these applications face the penetration depth challenges discussed earlier.

Perhaps most intriguingly, researchers are exploring whether photobiomodulation can increase cell proliferation, including stem cell growth. If cells respond to certain wavelengths of light by multiplying more readily, this could have implications for regenerative medicine—though this research is still in early stages.

For chronic wounds, the picture remains murky. Higher-power lasers have sometimes successfully closed acute wounds as an alternative to stitches, but for chronic wounds that won't heal, reviews have found inconsistent results and low-quality research. The therapy isn't ready for widespread clinical application for wound healing.

The Bottom Line

Photobiomodulation is a real phenomenon. Light of certain wavelengths really does affect cellular processes through absorption by cytochrome c oxidase in mitochondria. This isn't pseudoscience or wishful thinking—it's photochemistry.

But the gap between "this is a real phenomenon" and "this is an effective treatment for condition X" is vast. For a handful of applications—preventing oral mucositis during cancer treatment, possibly stimulating hair growth in pattern baldness—the evidence is reasonably strong. For many other promoted uses, the evidence is weak, mixed, or simply doesn't exist yet.

The therapy's relative safety is reassuring, but it also enables a market flooded with devices making unsupported claims. Without serious side effects to discourage use, there's little natural check on overpromising.

What's genuinely fascinating is how a broken laser in a Hungarian laboratory in 1967 opened a window into light's effects on living tissue. Mester's accidental discovery—like Fleming's mold-contaminated petri dish leading to penicillin, or Röntgen's mysterious rays revealing bones—reminds us that science often advances through serendipity as much as intention.

The mice grew their fur back faster. More than fifty years later, we're still figuring out everything that means.