How Does High-Intensity Laser Therapy Actually Work?

Shining light on pain, inflammation and tissue recovery

If you’ve been treated at MassageRx, you may have seen me use the High-Intensity Laser as part of treatment.

At first glance, laser therapy can seem almost too simple.

There are no needles. Nothing is being injected. There is no electrical stimulation making a muscle contract. In many cases, all you feel is a comfortable warmth as the laser moves over the area being treated.

So how can shining light onto an injured or painful area potentially influence what is happening underneath the skin?

The answer takes us all the way down to the level of the cell.

And while we don’t yet understand every aspect of how therapeutic laser works, there is now a substantial body of research investigating both its biological mechanisms and its clinical effects.

First: this isn’t a surgical laser

When people hear the word “laser”, they often think about lasers used to cut, cauterise or destroy tissue.

Therapeutic laser is different.

The aim isn’t to damage tissue. Instead, specific wavelengths of red and near-infrared light are delivered into tissue with the intention of influencing biological processes.

This broader field is commonly called photobiomodulation (PBM).

Break that word down and it becomes much easier:

Photo = light

Bio = biology

Modulation = changing or influencing

Photobiomodulation therefore essentially means:

Using light to influence biological activity.

High-Intensity Laser Therapy (HILT) uses considerably higher power than traditional low-level laser devices, allowing a therapeutic dose of light energy to be delivered relatively quickly and potentially to deeper anatomical targets.

Importantly, though, “higher power” doesn’t automatically mean “better treatment”.

The wavelength, power, treatment area, energy delivered, tissue characteristics and treatment time all influence the biological dose.

What happens when laser light enters the body?

A useful way to think about this is to imagine sunlight hitting a dark surface.

The light isn’t simply sitting on the surface. Photons interact with molecules within that material.

Something similar happens biologically.

When therapeutic wavelengths of light enter tissue, some light is reflected, some is scattered, some is absorbed by superficial structures, and a proportion penetrates further into the tissue.

Certain molecules can absorb particular wavelengths of light. These light-sensitive molecules are known as chromophores.

Once photons are absorbed, they may influence cellular activity.

This is where things get particularly interesting.

Meet the mitochondria

Most people were taught at school that mitochondria are the:

“powerhouses of the cell.”

That’s actually a useful starting point.

Mitochondria help convert nutrients and oxygen into adenosine triphosphate (ATP) — one of the primary forms of usable energy within our cells.

ATP is required for an enormous range of biological processes involved in maintaining, repairing and functioning tissue.

One of the leading theories of photobiomodulation involves an enzyme within the mitochondrial respiratory chain called:

Cytochrome c oxidase (CCO)

Cytochrome c oxidase participates in the final stages of mitochondrial energy production and has long been proposed as an important photoacceptor for red and near-infrared light.

One hypothesis is that light can influence interactions between cytochrome c oxidase and nitric oxide (NO).

Nitric oxide can bind to components of the mitochondrial respiratory chain and influence cellular respiration. Under certain conditions, light may alter this interaction, potentially affecting mitochondrial membrane potential, oxygen utilisation and ATP production.

In simple terms:

Light enters tissue → photons are absorbed → cellular signalling changes → mitochondrial and metabolic activity may change.

However, there’s an important scientific qualification here.

The cytochrome-c-oxidase explanation is a leading model rather than a completely settled mechanism. Reviews of the mechanistic evidence have pointed out that some commonly repeated explanations of exactly how light interacts with CCO remain uncertain.

So it is more scientifically accurate to say that photobiomodulation appears capable of influencing mitochondrial and cellular signalling than to claim that laser simply “charges your mitochondria”.

But ATP is only the beginning

The interesting part of photobiomodulation isn’t simply an increase in cellular energy.

Light exposure appears capable of triggering a cascade of cellular signalling.

Research has investigated changes involving:

• nitric oxide (NO)
• reactive oxygen species (ROS)
• calcium signalling
• mitochondrial membrane potential
• transcription factors
• inflammatory signalling
• antioxidant pathways
• cellular proliferation and migration

This is important because relatively small changes at the cellular level can potentially initiate much larger downstream biological responses.

Think about flicking a light switch.

Your finger isn’t providing the electricity required to illuminate an entire building. It’s simply providing the signal that starts a much larger process.

Photobiomodulation may work in a somewhat comparable way.

The photon isn’t “healing” the tissue itself.

It may instead act as a biological signal that influences how cells respond to their environment.

What about inflammation?

This is another area where the terminology matters.

Inflammation isn’t inherently bad.

After injury, inflammation forms an essential part of the body’s repair response. Trying to completely “switch inflammation off” isn’t necessarily desirable.

Instead, photobiomodulation appears to have the potential to modulate inflammatory signalling.

Experimental research has reported effects on inflammatory mediators, oxidative signalling and cellular pathways involved in tissue repair.

That’s quite different from simply saying:

“Laser gets rid of inflammation.”

A better description would be:

Laser therapy may influence the cellular environment associated with inflammation and tissue recovery.

That distinction matters.

What about circulation?

Nitric oxide also plays an important role in blood vessel regulation.

Changes in nitric oxide availability and local vascular responses may therefore contribute to some of the effects observed following photobiomodulation.

Improved local microcirculation could theoretically influence oxygen availability, nutrient delivery and removal of metabolic by-products.

Again, though, it would be an oversimplification to say laser simply “increases blood flow and therefore heals tissue”.

Biology is considerably more complicated than that.

And then there’s pain

This is perhaps the most clinically relevant part of the discussion.

Laser therapy isn’t simply a “healing machine”.

Photobiomodulation has also been investigated for its effects on pain.

Potential mechanisms include changes in inflammatory signalling, local tissue environment, peripheral nerve activity and nociceptive processing.

This becomes particularly useful clinically because pain isn’t simply a direct measurement of tissue damage.

Pain is ultimately an output of the nervous system influenced by information coming from the tissues, previous experiences, inflammation, mechanical sensitivity, expectations and many other factors.

Reducing nociceptive input or changing the biological environment surrounding a sensitised structure may therefore help create a window in which movement and rehabilitation become more tolerable.

And this brings us to perhaps the most important part of the entire article.

Laser should rarely be the whole treatment

At MassageRx, I don’t view High-Intensity Laser Therapy as a magic wand.

For most musculoskeletal problems, simply lying on a treatment table while somebody applies a machine isn’t a complete rehabilitation strategy.

Instead, laser can be used as one component of a broader treatment plan.

Depending on the condition, that might include:

Assessment → Laser → Manual Therapy → Progressive Loading → Movement → Return to Activity

For example, if someone has an irritable tendon, reducing pain may allow us to introduce appropriate loading more comfortably.

If someone has an acutely painful joint, improving symptom tolerance may make movement easier.

If we’re treating a sports injury, laser may complement rather than replace the progressive rehabilitation required to restore the capacity of that tissue.

The goal isn’t simply:

“Make the pain disappear.”

The goal is:

Create the best possible environment for the person to move, rehabilitate and regain capacity.

Does the research support High-Intensity Laser Therapy?

There is encouraging evidence, but it needs to be interpreted carefully.

A large 2023 systematic review and meta-analysis examined 48 randomised controlled trials investigating High-Intensity Laser Therapy for musculoskeletal disorders.

The researchers found improvements in pain and function. Across the pooled studies, pain measured using a visual analogue scale decreased by approximately 1.3 cm more than comparison interventions, while functional outcomes also favoured HILT.

However, the authors rated the evidence for pain as low quality and function as moderate quality, and warned that many included trials had a high risk of bias.

That qualification is important.

Earlier meta-analyses have also reported improvements in pain and disability across musculoskeletal conditions, including spinal pain and knee osteoarthritis, but heterogeneity between treatment protocols and study quality remains a problem.

More recently, a 2026 systematic review and network meta-analysis compared High-Intensity and Low-Level Laser Therapy across 22 randomised trials involving 1,353 participants.

HILT produced statistically greater pain reductions in some comparisons, particularly when combined with exercise or other physiotherapy interventions.

But there was an important catch.

The differences were generally modest, often below thresholds considered clinically important, and the certainty of much of the evidence was rated very low.

That doesn’t mean laser doesn’t work.

It means the scientifically responsible conclusion is more nuanced:

High-Intensity Laser Therapy appears capable of reducing pain in some musculoskeletal conditions, but it should be viewed as an adjunct to good clinical management rather than a replacement for assessment, exercise and rehabilitation.

Why does the dose matter?

This is one of the most overlooked aspects of laser therapy.

Laser treatment isn’t simply:

Laser ON = therapeutic effect.

Several parameters influence the dose reaching the tissue:

Wavelength (nm)
Determines how light interacts with and penetrates biological tissue.

Power (Watts)
How rapidly energy is being delivered.

Energy (Joules)
The total amount of energy delivered.

Irradiance (W/cm²)
The power delivered relative to the treatment area.

Fluence (J/cm²)
The energy delivered relative to the treatment area.

Treatment time
How long the tissue is exposed.

Then we need to consider the patient.

Skin pigmentation, adipose tissue, treatment depth, vascularity, tissue type and the anatomical target can all influence how much light actually reaches the desired tissue.

This is why simply comparing the wattage of two laser machines tells us surprisingly little about the actual biological dose.

More isn’t necessarily better

One of the fascinating characteristics of photobiomodulation is what’s called a biphasic dose response.

In simple terms:

Too little energy may do very little.

An appropriate dose may produce the desired biological response.

Increasing the dose further doesn’t necessarily produce a better result.

This is another reason why the idea that the “most powerful laser must be the best laser” isn’t scientifically sound.

A high-powered therapeutic laser gives the clinician the ability to deliver substantial energy efficiently.

The skill lies in determining how much energy, where, and for what clinical purpose.

So what does the patient actually feel?

High-Intensity Laser Therapy is generally comfortable.

Depending on the treatment parameters and technique, patients commonly experience gentle warmth moving through the treatment area.

Because high-powered therapeutic lasers can generate significant thermal energy if used incorrectly, treatment technique and appropriate dosing matter.

Protective eyewear is also essential because therapeutic laser light can pose a significant hazard to the eyes.

Which conditions is laser used for?

Research has investigated HILT across a range of musculoskeletal conditions, including:

• tendinopathies
• knee osteoarthritis
• shoulder pain
• neck pain
• low-back pain
• plantar heel pain
• lateral elbow pain
• muscle injuries
• joint-related pain

However, evidence isn’t equally strong for every condition.

A positive study on knee osteoarthritis doesn’t automatically prove that the same treatment protocol will work for an Achilles tendon, rotator cuff or lumbar spine.

Condition-specific evidence and appropriate dosing matter.

The bottom line

High-Intensity Laser Therapy sits at an interesting intersection between physics, cellular biology and rehabilitation medicine.

At its simplest:

We’re using specific wavelengths of light to influence biological processes within tissue.

At the cellular level, photobiomodulation appears capable of influencing mitochondrial function and signalling involving nitric oxide, reactive oxygen species, calcium and numerous downstream pathways.

At the tissue level, these processes may influence inflammatory signalling, pain, vascular responses and aspects of tissue recovery.

At the clinical level, research suggests HILT can improve pain and function in some musculoskeletal conditions — although the quality of evidence varies considerably and there is still much we need to learn about optimal dosing and which patients are most likely to benefit.

And perhaps most importantly:

Laser doesn’t replace rehabilitation.

If I can use laser therapy to reduce pain or irritability enough that you can move better, tolerate loading, perform your rehabilitation and progressively return to what you enjoy doing, then it has served a valuable purpose.

The technology may be sophisticated.

But the objective remains very simple:

Treat smarter. Move better. Build capacity. Get back to doing what matters.

References & further reading

de la Barra Ortiz HA, Parizotto NA, Liebano RE. Comparison of the effectiveness of high-intensity laser therapy versus low-level laser therapy in musculoskeletal disorders: a systematic review and network meta-analysis. Lasers Med Sci. 2026.

Martínez-Pozas O, et al. High-Intensity Laser Therapy for Musculoskeletal Disorders: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. J Clin Med. 2023.

Song HJ, Seo HJ, Kim D. Effectiveness of high-intensity laser therapy in the management of patients with knee osteoarthritis: A systematic review and meta-analysis of randomized controlled trials. J Back Musculoskelet Rehabil. 2020.

Alayat MSM, et al. The effectiveness of high intensity laser therapy in the management of spinal disorders: A systematic review and meta-analysis. J Back Musculoskelet Rehabil. 2019.

Quirk BJ, Whelan HT. What Lies at the Heart of Photobiomodulation: Light, Cytochrome C Oxidase, and Nitric Oxide—Review of the Evidence. Photobiomodul Photomed Laser Surg. 2020.

Hamblin MR. Mechanisms and Mitochondrial Redox Signaling in Photobiomodulation. Photochem Photobiol. 2018.