What Is Photobiomodulation (PBM)? How Light Can Influence Cellular Activity

Light is more than something that allows us to see. At specific wavelengths and exposure levels, light can interact with biological tissues and influence cellular processes.

This is the scientific principle behind photobiomodulation (PBM), a field of research investigating how red and near-infrared light can influence biological activity without relying primarily on heat.

Photobiomodulation is used in some clinical applications and continues to be studied for skin health, hair growth, wound healing and other conditions. However, its effects depend on the treatment protocol, device and intended application.

In this guide, we explain what PBM is, how it may work, how it differs from heat therapy, and what the research tells us so far.

1. What Is Photobiomodulation?

Photobiomodulation is the use of non-ionising light to influence biological processes in living tissue.

The light sources used in PBM can include:

• Light-emitting diodes (LEDs).
• Low-power lasers.
• Other suitable visible or near-infrared light sources.

The term photobiomodulation combines three ideas:

• Photo: Light.
• Bio: Living organisms or biological systems.
• Modulation: A change in activity or function.

In simple terms, PBM investigates how appropriately delivered light can influence the activity of cells and tissues.

It is sometimes called low-level light therapy or low-level laser therapy. The broader term PBM is useful because the technology is not limited to lasers; LED devices can also be used.

An important distinction is that PBM is intended to produce biological effects through light interactions rather than primarily through heating tissue.

2. How Does Photobiomodulation Work?

To understand PBM, imagine that light reaches the surface of your skin and enters the tissue beneath it.

Some light is reflected, some is scattered, and some is absorbed by molecules within the tissue. When certain molecules absorb photons, they can undergo changes that influence biological signalling.

These changes may affect processes involved in cellular energy production, inflammation, oxidative signalling and tissue responses.

Researchers are investigating several possible mechanisms, including interactions with mitochondrial proteins and light-sensitive molecules in cells.

The exact mechanism is not fully established for every wavelength, device or application. PBM should therefore be understood as an active area of scientific research rather than a single mechanism that explains every reported result.

3. What Role Do Mitochondria Play?

Mitochondria are structures inside many cells that help produce adenosine triphosphate (ATP), a molecule used to transfer energy within cells.

One proposed mechanism of PBM involves cytochrome c oxidase, a protein complex in the mitochondrial electron transport chain.

Researchers have investigated whether light absorption can influence mitochondrial activity and downstream cellular signalling. Depending on the circumstances, these responses may involve changes in ATP-related activity, reactive oxygen species and other signalling pathways.

However, it would be an oversimplification to say that red light automatically increases cellular energy in every tissue. Biological responses depend on the light exposure, the cells involved and their existing condition.

PBM research continues to examine these mechanisms and how they relate to measurable outcomes in humans.

4. Why Are Red and Near-Infrared Light Used?

Red and near-infrared wavelengths are commonly studied in PBM because they interact with biological tissue in ways that make them useful for particular research and clinical applications.

Two frequently discussed wavelengths are:

660 nm red light

This wavelength is visible to the human eye. Researchers have investigated red-light PBM in areas such as skin-related applications, wound healing and cellular responses.

850 nm near-infrared light

This wavelength is invisible to the human eye. Under comparable conditions, near-infrared light can often penetrate farther into tissue than shorter visible wavelengths, although the actual light distribution depends on tissue properties and treatment conditions.

Neither wavelength is universally better than the other. The appropriate wavelength depends on the intended application and the complete treatment protocol.

A device that combines red and near-infrared LEDs can deliver both wavelength ranges, but combining them does not automatically establish superior results.

5. What Is the Difference Between PBM and Heat Therapy?

Although both methods can involve energy reaching the body, photobiomodulation and heat therapy are different approaches.

A red light therapy pad may feel warm during use, depending on its design and operating conditions. That does not by itself prove that PBM is occurring or that the treatment is effective.

Likewise, a device that produces heat should not automatically be described as a photobiomodulation device simply because it uses electrical energy or emits a visible glow.

6. What Health Applications Have Been Studied?

PBM has been investigated in several medical and aesthetic fields. The strength of the evidence varies by condition.

Skin and wound healing

Researchers have studied PBM for wound healing and certain skin-related applications. The evidence depends on the specific condition, device and treatment protocol.

Hair growth

Red-light and laser-based devices have been studied for androgenetic alopecia, a common form of hereditary hair loss. Some evidence supports benefits from specific devices and protocols.

Pain and musculoskeletal conditions

PBM has been investigated for selected pain conditions and musculoskeletal problems.

Other clinical applications

Researchers are also studying PBM in additional areas, including neurological and other medical applications. Many of these uses remain under investigation and require further high-quality research.

A 2025 evidence-based consensus paper identified selected clinical applications for which PBM may be useful, including androgenetic alopecia, peripheral neuropathy and certain wound-related conditions. These findings relate to particular clinical indications and do not establish that all consumer light therapy devices are effective.

Read the 2025 evidence-based consensus on the clinical application of photobiomodulation.

7. Does More Light Mean Better Results?

No. A higher output does not automatically mean a better biological response.

PBM depends on several parameters working together.

Wavelength: The wavelength influences how light interacts with tissue.

Irradiance: This describes optical power delivered per unit area and is commonly expressed in mW/cm².

Fluence: This describes energy delivered per unit area over a specified exposure and is commonly expressed in J/cm².

Exposure time: The duration of treatment affects the total energy delivered when output remains constant.

Treatment geometry: Distance, beam spread, contact conditions and the size of the treatment area affect how light reaches the tissue.

PBM research also discusses a biphasic dose response: under some conditions, a biological response may improve within a particular dose range but become smaller or change when the dose is too low or too high.

This means that simply increasing the power or extending the treatment time is not a reliable way to improve results. Appropriate parameters depend on the intended application and supporting evidence.

8. How Can You Evaluate a Photobiomodulation Device?

If you are considering a home-use device, look beyond its advertised benefits.

Check the following:

1. Wavelength specifications: Are the wavelengths stated clearly?
2. Measured optical output: Does the manufacturer provide credible irradiance data?
3. Measurement conditions: Is the distance and measurement method documented?
4. Treatment instructions: Are duration, frequency and positioning explained?
5. Safety information: Are relevant precautions and limitations provided?
6. Evidence for the intended use: Does the research support the particular application being advertised?
7. Product quality: Are the construction, warranty and quality-control arrangements clear?

Be cautious of claims that a device can treat numerous unrelated conditions or that a higher irradiance number automatically proves superior performance.

A study involving a particular clinical device and protocol does not demonstrate that every product using the same wavelength will produce the same result.

9. Is Photobiomodulation Safe?

Safety depends on the device, wavelength, optical output, exposure duration, treatment area and individual circumstances.

Follow the manufacturer’s instructions and do not stare directly into LEDs or laser sources. Near-infrared light is invisible, so the absence of visible brightness does not mean that the light is harmless to the eyes.

Consult a qualified healthcare professional before using PBM for a medical condition, especially if you have a condition that affects light sensitivity or take medication that increases photosensitivity. Do not replace prescribed treatment with an unverified consumer device.

Conclusion

Photobiomodulation is a field of research exploring how appropriately delivered light can influence biological activity.

Red and near-infrared light can interact with tissue and may influence cellular signalling, mitochondrial activity and other biological processes. Researchers have investigated PBM for several clinical applications, although the strength of evidence varies considerably between conditions.

The effectiveness of a treatment depends on more than its wavelength or LED count. Optical output, dose, exposure time, device design and the intended application all matter.

Understanding the science behind photobiomodulation helps consumers evaluate light therapy products more critically and distinguish established evidence from claims that still require research.

Disclaimer: This article is for educational purposes only and is not medical advice. The evidence for photobiomodulation varies by condition, device and treatment protocol. Consult a qualified healthcare professional about medical conditions or treatment decisions.

References

1. Evidence-Based Consensus on the Clinical Application of Photobiomodulation (2025)
2. Effects of Photobiomodulation on Multiple Health Outcomes: An Umbrella Review of Randomized Clinical Trials (2025)
3. Devices Used for Photobiomodulation of the Brain: A Comprehensive and Systematic Review (2024)
4. Light Buckets and Laser Beams: Mechanisms and Applications of Photobiomodulation Therapy