Photobiomodulation: what is really behind light therapy - mechanism, evidence and safe use

Your ophthalmologist talks about light therapy for dry age-related macular degeneration (AMD), a condition for which there was long little hope. Your physiotherapist recommends red light for chronic neck pain. And online, elite athletes swear by light panels for recovery. At the same time, professional societies warn against premature conclusions and call for more studies. How does this fit together?

The answer lies in one term: photobiomodulation (PBM). Behind it is the targeted use of red and near-infrared light to initiate cellular processes. It is a purely photochemical mechanism and has nothing to do with heat. The distinction is important: PBM is not an infrared sauna, not a daylight lamp for winter depression and not UV therapy. However, the terms LLLT (low-level laser therapy) and red light therapy are closely related.

This article sheds light on the topic. You will understand the mechanism of action at cellular level, learn about the scientific evidence for the three most important application fields and be able to assess limitations and safety aspects. After reading it, you will know when a medical consultation is essential and what to pay attention to during use.

What is photobiomodulation? Definition, distinction and overview

To understand photobiomodulation, we must first clarify what it is, where the term comes from and what it must be clearly distinguished from. This section serves as an orientation map before we dive deeper into the biological mechanisms and clinical applications.

Photobiomodulation definition: the current technical term and its history

The photobiomodulation is the use of light from the red (approx. 600-700 nm) and near-infrared (approx. 700-1100 nm) spectrum to regulate biological processes at cellular level. The decisive point is that this occurs without significant heat generation (non-thermal). Put simply: light of certain wavelengths "talks" to our cells and encourages them to work.

The history of this therapy form explains today's confusion of terms:

• Antiquity: The ancient Greeks and Egyptians already used sunlight (heliotherapy) for healing purposes.
• 1967: The Hungarian physician Endre Mester accidentally discovers that a weak laser stimulates hair growth in mice and accelerates wound healing. He coins the term LLLT (low-level laser therapy).
• LLLT era: For decades the term LLLT is used, although LEDs (light-emitting diodes) are increasingly used instead of lasers.
• Since around 2014: To reflect the fact that not only lasers but also LEDs can be effective, and that the mechanism is a modulation (regulation) rather than pure stimulation, the more precise term photobiomodulation (PBM) has become established in the professional world.

In German-speaking countries, the term photobiomodulation has not yet fully arrived in everyday language. Many people therefore still search for "LLLT" or "red light therapy", but mean the mechanism of PBM.

Photobiomodulation vs. red light therapy, LLLT and infrared sauna: table

The terms are often used synonymously, but they refer to different things. The following table provides clarity:

The most important distinction: while the infrared sauna primarily works through heat, the effect of photobiomodulation is photochemical. The light itself is the trigger, not the temperature.

How does photobiomodulation work? The mechanism at cellular level

How can light without heat produce a biological effect? The answer lies in the power plants of our cells, the mitochondria. This is where the central process takes place that triggers all further effects.

The primary target of red and near-infrared light is an enzyme called cytochrome c oxidase. It is the final component (complex IV) in the mitochondrial respiratory chain, the production line for our cellular energy, adenosine triphosphate (ATP).

The chain of effects can be described simply as follows:

1. Light absorption: Photons (light particles) of the appropriate wavelength hit cytochrome c oxidase and are absorbed.
2. Blockade is released: Under stress conditions, nitric oxide (NO) can bind to this enzyme and slow energy production. Light energy releases this NO binding.
3. Energy production increases: The enzyme is now free again, and the respiratory chain can run at high speed. Electron transport is accelerated, leading to increased ATP production.
4. Cellular signals are triggered: This energy boost acts like a starting signal. It activates a cascade of cellular repair and growth processes by influencing important switches in the cell, transcription factors such as NF-kappaB.

A decisive principle here is the biphasic dose response (also called the Arndt-Schulz law): too little light has no effect. An optimal dose is stimulatory. Too much light, however, can overwhelm cells, damage them and produce the opposite effect.

From cell to tissue: what happens after light absorption?

The rise in ATP in the individual cell has far-reaching consequences for the entire tissue:

• Anti-inflammatory effect: PBM can reduce the production of pro-inflammatory messenger substances while promoting anti-inflammatory ones. This is crucial for pain relief and healing.
• Pain relief: Light therapy can slow the conduction speed of pain-carrying nerve fibres and stimulate the release of the body's own pain-relieving substances such as endorphins.
• Tissue regeneration: The surplus energy enables cells to divide faster and produce important building blocks such as collagen. This accelerates wound healing and repair of damaged tissue.
• Improved circulation: PBM can lead to widening of blood vessels, improving blood flow and therefore oxygen and nutrient supply in the treated area.

Which of these effects is most prominent depends strongly on the parameters used.

Wavelength, penetration depth and dosage: the three control variables

Not every red light is the same. The therapeutic success of a photobiomodulation therapy depends on three critical factors:

1. Wavelength (in nanometres, nm): It determines how deeply light penetrates the tissue and which molecules absorb it.
   • Red light (approx. 630-670 nm): Penetrates less deeply (a few millimetres) and acts primarily on skin and mucous membranes.
   • Near-infrared light (NIR, approx. 800-850 nm): Penetrates several centimetres deep and reaches muscles, joints and tendons.
2. Penetration depth: This is influenced not only by wavelength, but also by the distance between the device and the skin. Direct skin contact gives the highest light penetration. Even at a distance of 2 cm, more than 90% of light output can be lost through scattering and reflection.
3. Dosage (fluence, in joules/cm²): This is the amount of energy that reaches the tissue per unit area. The therapeutic window is narrow depending on the indication. Too little energy is ineffective; too much can be harmful.

These parameters explain why a photobiomodulation device for home use works differently from photobiomodulation laser therapy in a clinic.

Photobiomodulation therapy: three application fields, one mechanism

Although the basic mechanism, activation of the mitochondria, is always the same, PBM is used in very different medical fields. We focus on the three areas with the most current and most discussed data.

Ophthalmology: PBM for dry AMD

In dry age-related macular degeneration (AMD), photoreceptor cells in the centre of the retina die, leading to progressive loss of vision. Until now, there has been no approved standard therapy. PBM with special light therapy systems (wavelengths 590, 660 and 850 nm) is being investigated here as an experimental approach.

However, the study situation is contradictory and is intensely discussed among specialists:

• Positive signals: Earlier studies showed promising results such as reduction of deposits under the retina (drusen) and improvement in visual acuity.
• The decisive LIGHTSITE III study: This larger study confirmed a statistically significant improvement in visual acuity. The PBM group gained an average of +5.4 letters on the eye chart, while the control group gained +3.0 letters.
• Why professional societies urge caution: Experts criticise the clinical relevance of this difference of only 2.4 letters. More serious, however, is a safety signal: in the PBM group, 41.7% of patients developed potentially harmful new blood vessel formation, compared with 25.0% in the control group.

Because of this data situation, the German Ophthalmological Society (DOG), the Retinological Society (RG) and the Professional Association of German Ophthalmologists (BVA) published a joint statement on 4 July 2025. It recommends that PBM for dry AMD should currently be used only within clinical studies.

Sports medicine and recovery: PBM for performance and recovery

In elite sports and rehabilitation, PBM is used to accelerate recovery and improve performance. Typical areas of use include:

• Reduction of muscle soreness (DOMS)
• Acceleration of muscle recovery after exertion
• Performance enhancement before training (pre-conditioning)

The mechanism here is based on increased ATP production in muscle cells, improved circulation and reduction of inflammatory markers. Numerous studies show positive effects, but the protocols used vary widely, so there is not yet a uniform gold standard.

One interesting aspect is chronobiology: the timing of application appears to be decisive. Use before training can prepare the muscles for load, while use afterwards supports repair processes. Some experts also point to positive effects on circadian rhythm and sleep quality, which further improves recovery.

Pain therapy and inflammation modulation: PBM for myofascial pain and chronic complaints

The field with perhaps the most robust evidence is pain therapy, especially myofascial pain syndrome (MPS), which is characterised by painful trigger points in the muscles.

A comprehensive 2022 meta-analysis including 17 high-quality studies with 441 patients found the following:

• PBM alone: showed moderate effectiveness in reducing pain.
• PBM combined with stretching exercises: showed a large effect and was therefore significantly more effective than PBM alone.

The quality of evidence was rated low to moderate, meaning the results still need confirmation by future studies.

There are also positive indications for other painful and inflammatory conditions, for example:

• Herpes labialis (cold sores): A meta-analysis showed that LLLT can shorten healing time by an average of 1.37 days.
• Carpal tunnel syndrome and chronic neck pain: Studies also suggest a pain-relieving effect here.

What do professional societies really say? Overview of the evidence

As the AMD example shows, there is often a gap between recommendations from individual practices and official statements by professional societies. To understand this discrepancy, it helps to look at the hierarchy of scientific evidence: an individual practice report carries less weight than a large controlled study or an official guideline.

In the case of PBM for AMD, the claim by some practices that it is the "only evidence-based option" stands against the clear DOG/RG/BVA recommendation to use the therapy "only within clinical studies". The professional societies' criticism of the decisive LIGHTSITE III study is well founded and relevant for patients:

• Heterogeneous study group: Patients with very different AMD stages were included.
• Questionable data handling: The statistical analysis is criticised as not fully transparent.
• Serious safety signal: The increased risk of new blood vessel formation (41.7% vs. 25.0%) is considered a clear warning signal.

This does not mean that PBM is ineffective for AMD. It does mean, however, that the current data are not sufficient to make a general recommendation outside controlled studies.

Recommendation for patients: Before starting PBM therapy, especially for eye diseases, always speak with your specialist. Ask specifically about the current position statement from the professional societies and obtain written cost approval from your health insurer before treatment begins.

How should study results be read correctly? Statistically significant does not equal clinically relevant

A common misunderstanding is confusing statistical significance with clinical relevance.

• Statistical significance (p-value): only states that a result is probably not due to chance. It says nothing about the size or practical meaning of the effect.
• Clinical relevance (effect size): describes how strong the effect is. In the LIGHTSITE III example, the difference of +2.4 letters was statistically significant, but many experts question whether a patient notices such a small difference in everyday life at all.
• Confidence interval (CI): indicates the range in which the true value is likely to lie. A very wide interval indicates great uncertainty.

For patients, this means: do not ask only whether a therapy works, but also how strongly it works and how secure the data are.

What does a PBM treatment look like? Process, duration and long-term plan

The specific course of PBM treatment varies greatly depending on the indication. The well-documented protocol for treating dry AMD is used here as a reference:

1. Initial examination and indication: A specialist, here an ophthalmologist, determines after a thorough examination whether the therapy is suitable.
2. Information consultation and cost clarification: The patient is informed about the process, chances of success, risks and costs.
3. Treatment cycle: The first cycle usually consists of 9 sessionsspread over a period of 3 to 5 weeks . Each session lasts only a few minutes per eye.
4. Follow-up: About 4 months after the first cycle, a follow-up examination is performed to assess the effect.
5. Monitoring and repetition: To maintain the effect, usually 2 to 3 treatment cycles per year are necessary.

In sports medicine protocols are more flexible, for example 2-3 sessions per week over 2-4 weeks. In pain therapy 10-15 sessions may be required, taking place daily or several times per week depending on acuity.

What does photobiomodulation cost? Costs and insurance coverage in Germany, Austria and Switzerland

The question of cost is decisive for many patients. The situation in the DACH countries is as follows (as of 2025):

Important note: The situation regarding cost coverage can change. Always check the current status directly with your insurer.

Who is PBM not suitable for? Contraindications and safety notes

Although PBM is considered to have few side effects, there are important contraindications and safety notes.

General contraindications:

• Epilepsy or migraine: Pulsed light in particular can trigger seizures in sensitive people.
• Photosensitivity: People with disease-related or medication-related photosensitivity, for example from certain antibiotics or diuretics, should avoid PBM.
• Active cancer: Direct irradiation of a tumour is contraindicated.
• Pregnancy: As a precaution, use in the abdominal and back area is discouraged.
• Fever and acute systemic infections.

Special considerations in ophthalmology: The increased risk of macular neovascularisation (41.7% vs. 25.0% in the LIGHTSITE III study) is the most important safety concern in AMD treatment. This must be discussed in detail with the ophthalmologist before therapy begins.

Eye safety: Never look directly into the light source of high-powered LEDs or lasers. When using laser devices, wearing protective glasses is mandatory.

Home use of PBM: parameters, checklists and safety limits

More and more PBM devices such as LED panels or handheld lamps are available for home use. Special caution is needed here because dose is decisive: too much can be harmful.

When buying, look for CE certification as a medical device and clear information on wavelength (nm) and power density (mW/cm²).

Daily checklist for safe home use:

1. Check the device: Is the device working properly?
2. Clean the area: The skin area to be treated should be clean and dry.
3. Put on protective glasses: Even with LED devices, glasses are recommended to protect the eyes, especially when used on the face.
4. Keep distance and time: Follow the manufacturer's instructions exactly. Never exceed the recommended treatment time.
5. Observe the reaction: Mild temporary redness can be normal. Pain or strong heat are warning signs.
6. Document: Keep a short log of date, duration, treated area and your reaction.

When should I see a doctor? Clear trigger conditions for home use

Pause home use and consult a doctor if any of the following occur:

• Your pain increases during or after use.
• Skin redness or swelling occurs and lasts longer than 24 hours.
• You notice unexpected changes, for example in moles in the treatment area.
• When used in the head area: onset or worsening of headaches or visual disturbances.
• Your symptoms do not improve after 2-3 weeks of regular use or even worsen.

Home use does not replace medical diagnosis. It should be considered only for known, uncomplicated complaints, such as muscle soreness, and after more serious causes have been ruled out.

Frequently asked questions (FAQ) about photobiomodulation

1. What is the difference between photobiomodulation and simple red light therapy? Red light therapy is a colloquial term that usually refers only to visible red light (approx. 630-700 nm). Photobiomodulation is the scientific umbrella term that also includes deeper-penetrating near-infrared light (approx. 700-1100 nm) and describes the precise non-thermal mechanism of action.

2. How long does the effect of PBM treatment last? This depends strongly on the indication. For acute problems such as muscle soreness, one session may be enough. For chronic conditions such as AMD or osteoarthritis, the effect is often temporary and must be maintained through regular treatment cycles, for example 2-3 times per year.

3. Is the treatment painful and are there side effects? The treatment itself is painless and non-invasive. At most, a very slight warming may be felt. Side effects are rare, but can occur with incorrect dosing or failure to observe contraindications, such as temporary skin redness. In AMD treatment, studies observed an increased risk of new blood vessel formation.

4. Can I use PBM safely at home? Yes, home use is possible, but it requires responsibility. Use only certified devices, follow the manufacturer's instructions exactly and start with shorter treatment times. If you have pre-existing conditions, especially of the eyes or skin, medical consultation before first use is essential.

5. Does health insurance cover photobiomodulation? In Germany, PBM is generally not covered by statutory health insurance and must be paid for privately as an IGeL service. Private insurers may cover costs in individual cases. In Switzerland and Austria it is also usually a private service. A prior request for cost coverage from your insurer is always advisable.

Conclusion: a tool with potential and responsibility

The photobiomodulation is more than just a wellness application. It is a serious therapy form with a well-understood cellular mechanism of action. Its potential to inhibit inflammation, relieve pain and promote regeneration is already well documented in pain therapy and sports medicine.

At the same time, the example of dry AMD shows how important critical evaluation of the evidence is. Not everything that is technically possible and promising in early studies withstands strict review by professional societies. The tension between innovative potential and scientific confirmation will continue to shape the discussion around PBM.

For patients and users, this means: inform yourself thoroughly, remain critical of healing promises and always consult a qualified specialist before making any therapy decision, especially in serious diseases. Used correctly and responsibly, light could become an even more important tool in medicine in the future.