Photobiomodulation, often abbreviated PBM, is not just about shining light on the skin. The method is based on the fact that specific wavelengths of red and infrared light can influence biological processes all the way down at the cellular level. When you read the research in this area, much points in the same direction: the central mechanism appears to start in the mitochondria.

Mitochondria are often called the cell’s power plants. This is where the cell produces ATP, the energy currency that almost all biological processes depend on. If the mitochondria work more efficiently, it can affect everything from recovery and tissue repair to skin function and the way cells respond to strain.

That is also why photobiomodulation should not be understood as a general light treatment where all light does the same thing. The effect is linked in particular to specific wavelengths, specific doses and specific targets in the cell.

• ordinary room light
• heat alone
• non-specific wellness
• random exposure without a target and dose

Photobiomodulation at the cellular level

At the cellular level, photobiomodulation is described as a biological response to light energy. The key is that the light is absorbed by molecules in the tissue that can convert this energy into chemical and electrical changes. In the research literature, such light-sensitive molecules are referred to as chromophores.

In mammalian cells, several review articles indicate that the mitochondria are the most important site for this absorption. More specifically, the enzyme cytochrome c oxidase, which is part of the respiratory chain’s complex IV, is highlighted. This is where photobiomodulation becomes interesting, because the mechanism is not primarily about the surface, but about the cell’s energy metabolism.

That is an important distinction.

So when red and infrared light hits tissue, some of the energy can reach cellular targets that affect respiration, redox balance and signalling molecules. That is the biological explanation that makes PBM different from light that is only used for illumination or heating.

Mitochondria as a target for red and infrared light

Mitochondria produce ATP through the electron transport chain. Here, electrons are moved between a series of complexes in the inner mitochondrial membrane, and this process builds up a proton gradient. The proton gradient then drives ATP synthase, which forms ATP.

Several sources suggest that red and infrared light can stimulate activity in complex IV, i.e., cytochrome c oxidase. When this enzyme is affected, it can change the rate and efficiency of mitochondrial respiration. This makes the mechanism very concrete: the light is not just linked to a diffuse feeling of wellbeing, but to a specific enzyme at a specific step in the cell’s energy production.

A simple way to view the mechanism is this:

The table should be read as a simplification. Biology is rarely linear, and the response depends on cell type, tissue condition and light dose. Even so, this chain from light absorption to altered mitochondrial function is one of the most consistent explanations in the research.

Cytochrome c oxidase and complex IV in the respiratory chain

Cytochrome c oxidase is the final enzyme complex in the electron transport chain. Its job is to pass electrons on to oxygen so that mitochondrial respiration can continue. When the enzyme works efficiently, it supports the entire energy-producing process.

Review articles on PubMed describe this enzyme as a central photoreceptor target for photobiomodulation. Some articles also highlight that stimulation of complex IV can increase catalytic activity and thereby support ATP formation. This is a major part of the explanation for why PBM is so often discussed in relation to energy, recovery and cellular function.

ATP synthesis and altered cellular energy

ATP is not just “more energy” in a loose sense. ATP is the direct energy source that cells use for muscle contraction, ion pumps, protein synthesis, membrane repair and regulation of many signalling pathways. When mitochondria produce ATP more efficiently, the cell can have better working conditions.

This does not mean that any light treatment automatically produces a strong biological effect. Nor does it mean that all cells respond the same way. But it explains why photobiomodulation is often associated with stressed tissue, recovery after activity and processes where energy demand is high.

Put very simply: if the cell gets better access to the energy it is already designed to use, it can more easily do its normal work.

Nitric oxide and mitochondrial redox signalling

Another central line of research concerns nitric oxide and mitochondrial redox signalling. Here, photobiomodulation becomes more than just ATP. The cell also uses small chemical signals to regulate how it responds to stress, oxygen conditions and injury.

Some research articles describe that cytochrome c oxidase is not only involved in energy production, but also relates to nitric oxide. Part of the hypothesis is that light can affect nitric oxide binding at the enzyme, making respiration easier. As this inhibition decreases, electron transport can proceed more freely.

At the same time, changes can occur in the redox balance. It sounds technical, but the basic idea is simple: the cell detects small shifts in oxidation and reduction and uses them as signals. Those signals can matter for gene expression, inflammation, cell protection and tissue repair.

This is where photobiomodulation becomes particularly interesting in research, because the effect is not only about immediate energy, but also about how the cell regulates itself afterwards.

Why stressed cells may respond differently to photobiomodulation

An important point in the literature is that healthy and stressed cells do not necessarily respond the same way. A cell that is already functioning close to normal may have less to gain than a cell that is metabolically pressured or operating under less favourable conditions.

This may help explain why PBM is often studied in contexts such as recovery, inflammation, wound healing and tissue that has been subjected to strain. Here, a change in energy production and signalling pathways may have greater practical significance than in tissue that is already fully functional.

That is why it makes sense to think in terms of the biological starting point, not only the type of lamp or device.

• Healthy cells: often respond more mildly because energy status is already stable
• Stressed cells: may be more receptive to changes in respiration and ATP formation
• Stressed tissue: may have a greater need for regulation of inflammation and repair
• Dose: both too little and too much light can produce a less clear benefit

Wavelengths, tissue penetration and dose in light therapy

When talking about red and infrared light, it is not only about colour, but about wavelength. Different wavelengths penetrate tissue differently and interact differently with biological structures. Red light is often used for more superficial targets, while infrared light is typically associated with deeper tissue.

This does not mean that “deeper” is always better. The choice depends on the purpose. Skin, superficial wounds and cosmetic targets may require a different approach than muscles, tendons or structures near joints. The biological mechanism is related, but the light’s path through the tissue is not the same.

Dose is at least as important as wavelength. Here, you typically look at power, exposure time, distance, treatment area and total energy. Two devices can both use red or infrared light, yet still deliver very different treatment in practice.

When assessing equipment, it is therefore sensible to look beyond marketing.

• documented wavelengths
• stated power and energy density
• CE approval
• clear instructions for use
• use for the correct body area

What the mechanism may mean for recovery, skin and tissue

When research links photobiomodulation to mitochondria, it is not about a single effect. It is about the fact that the cell’s energy system influences many functions at the same time. Tissue that needs to repair itself, reduce irritation or rebuild normal function depends on energy and signalling.

That is why PBM is studied, among other things, in relation to:

• muscles and recovery
• wound healing
• skin structure
• inflammatory processes
• tissue regeneration

In the skin area, improved cellular activity may be relevant for processes involving collagen, repair and local circulation. In muscles and tendons, the focus is often on recovery after strain and support for normal healing processes. Research also describes anti-inflammatory effects as a relevant line of inquiry, but the response depends on the situation and should not be understood as uniform across all conditions.

The key point is that the mechanism points back to the mitochondria—not as the full explanation for everything, but as the most robust biological starting point.

Practical use of photobiomodulation at home and in the clinic

In practice, photobiomodulation exists as both light therapy and medical laser. Both approaches work with targeted light, but they can be designed differently depending on whether the purpose is a small, precise area or a larger treatment field. Handheld devices, pads, masks and larger applicators are therefore used for different needs.

For home use, it is often an advantage to have equipment that makes it easy to maintain the correct distance, treatment time and placement. In clinical use, the need may be for greater flexibility, more precise dosing or access to more types of applicators. Regardless of format, the same biological principle is being applied: delivering an appropriate amount of red or infrared light to the tissue so the cells’ response can be activated.

There are four things in particular worth looking out for when choosing a device:

• Safety: choose equipment with CE approval and clear instructions
• Purpose: face, joints, muscles and larger body areas do not always require the same solution
• Usage pattern: short, regular treatments are often easier to stick with than sporadic use
• Documentation: stated technical data makes it easier to assess what the device actually delivers

The most useful question is rarely whether light “works” in a general sense. The better question is which light, at what dose, for which tissue and with which biological target. When photobiomodulation is viewed through that lens, mitochondria are not a side note, but the very focal point.