Photobiomodulation Effects on Macrophages: What Current Evidence Actually Shows

Updated on August 20, 2026 | Estimated reading time: 13 minutes

"Red light therapy boosts your immune system" is a stronger claim than current evidence supports. A more precise question is: what are the photobiomodulation effects on macrophages, and do those cellular effects translate into better immune function in people?

Photobiomodulation (PBM), also called red light therapy or low-level light therapy, uses visible red or near-infrared light to influence biological activity through primarily non-thermal mechanisms. Laboratory and animal research suggests that PBM can alter selected macrophage signals under defined conditions. However, these findings do not establish a generalized "immune boost," protection against infection, or a universal treatment protocol.

Macrophages are involved in innate immune defense, debris clearance, inflammatory signaling, and tissue repair. Their response to PBM appears to depend on wavelength, irradiance, radiant exposure, timing, tissue state, and the experimental model. The most defensible conclusion is therefore that PBM may modulate macrophage behavior in specific contexts—not that it uniformly activates or suppresses the immune system.

This article reviews the proposed mechanisms, macrophage polarization research, evidence limitations, wavelength and dose considerations, and practical safety questions. It is an evidence review, not a treatment recommendation.

What Are the Photobiomodulation Effects on Macrophages?

Conceptual interaction between red and near-infrared light and macrophages

Macrophages are highly adaptable immune cells. Some live permanently in tissues, while others develop from circulating monocytes that enter an area after injury or infection. Depending on their local environment, macrophages can engulf microbes and damaged material, release inflammatory mediators, present antigens, coordinate other immune cells, and help guide the transition from inflammation to tissue repair.

PBM research has reported changes in several macrophage-related outcomes:

• expression of inflammatory mediators such as TNF-α, IL-1β, IL-6, and inducible nitric-oxide synthase;
• expression of repair-associated mediators such as IL-10, TGF-β, and arginase-related markers;
• mitochondrial activity, redox signaling, calcium movement, and membrane potential;
• phagocytosis, viability, migration, and interactions with other cells;
• the relative abundance of macrophages displaying different activation markers in injured tissue.

These effects are not uniform. The same wavelength can produce different results when the dose, cell state, measurement time, or tissue model changes. One in-vitro study of activated J774 macrophage-like cells found that 660 nm and 780 nm exposures reduced some inflammatory markers, while the 660 nm condition also increased IL-6 expression and production. The authors concluded that the response was time- and parameter-dependent rather than universally anti-inflammatory.[3]

A later cell study likewise found different changes at four and 24 hours after red or infrared PBM. At 660 nm, several inflammatory genes decreased four hours after exposure; at 780 nm, other changes appeared later, and TGF-β1 expression moved in different directions at different time points.[4] These results illustrate why "PBM reduces inflammation" is too broad unless the model, parameters, and observation time are specified.

Macrophage Polarization Is More Complex Than an M1-to-M2 Switch

Macrophage activation continuum rather than a binary M1/M2 switch

Macrophage polarization is often explained using two labels:

• M1-like macrophages are commonly associated with pathogen defense and pro-inflammatory signaling.
• M2-like macrophages are commonly associated with inflammation resolution, extracellular-matrix remodeling, and tissue repair.

This model is useful for explaining experiments, but it is an oversimplification. Human macrophages do not operate as a binary switch. They can display mixed markers, change over time, and respond differently across tissues, diseases, and stages of healing. An early inflammatory macrophage response can be necessary for clearing microbes and damaged material, while a later repair-associated response can help resolve inflammation. Neither state is automatically "bad" or "good."

Therefore, a study reporting more CD206-positive cells or fewer CD86-positive cells does not prove that PBM has "balanced the immune system." It reports a change in selected markers under that study's conditions. To establish clinical value, researchers must also show meaningful outcomes in the intended population and determine whether the macrophage change actually contributed to those outcomes.

What preclinical studies suggest

Cell and animal studies provide biological plausibility for photobiomodulation effects on macrophages:

• In activated macrophage-like cells, red and infrared PBM altered TNF-α, IL-6, iNOS, COX-2, chemokines, and TGF-β1 in wavelength-, dose-, and time-dependent patterns.[3,4]
• In a rodent skeletal-muscle injury model, PBM was associated with changes in macrophage phenotypes across different stages of tissue repair.[5]
• In a rat spinal-cord injury model, 810 nm PBM was associated with a greater proportion of repair-associated macrophage/microglia markers and functional changes. This was an injury-specific animal experiment, not evidence for a general immune-support routine.[6]
• In an animal model of oral ulcers, PBM was associated with wound changes and macrophage-polarization markers. It does not establish that the same effect occurs in every wound type or with an unrelated light source.[7]
• A 2025 review identified 19 experimental studies of PBM and macrophage polarization but also found substantial variation in energy density and methodology.[2]

The recurring lesson is not that one wavelength "converts M1 into M2." It is that PBM may influence a dynamic inflammatory environment under particular experimental conditions.

What human evidence does not yet establish

Direct human evidence is much thinner than the laboratory and animal literature. Many clinical PBM studies measure pain, function, wound area, or inflammatory biomarkers without collecting tissue-level macrophage data. Even when a clinical outcome improves, that does not prove macrophage polarization caused the result.

Current research does not establish that consumer red light therapy:

• reliably shifts macrophages from M1-like to M2-like states in healthy people;
• improves whole-body immune defense;
• prevents viral or bacterial infection;
• increases vaccine responses;
• creates a standard macrophage-targeting dose or body placement;
• treats autoimmune disease by "rebalancing" macrophages.

These remain research questions, not validated consumer claims.

How PBM May Influence Macrophage Signaling

Proposed PBM mechanisms involving macrophage signaling

PBM is being studied as a photochemical signaling intervention, not as a nutrient that simply "adds energy" to the immune system.

Cytochrome c oxidase (CCO), an enzyme in the mitochondrial electron-transport chain, is one proposed photoacceptor for red and near-infrared light. Other proposed mechanisms include light-sensitive ion channels, nitric-oxide signaling, changes in water structure, and alterations in cellular redox state. No single pathway fully explains every observed PBM response, and the U.S. Food and Drug Administration notes in its draft PBM guidance that mechanisms may vary by indication and are not fully understood.[1]

Under some experimental conditions, PBM is associated with changes in ATP production and a short-lived rise in reactive oxygen species that acts as a signal. In cells already experiencing oxidative stress, later antioxidant responses may reduce selected oxidative-stress markers. It is therefore inaccurate to say that PBM always "reduces ROS." The direction, magnitude, and timing of the response can differ.

Macrophage studies have explored signaling pathways including NF-κB, STAT, PI3K/AKT/mTOR, Notch1/HIF-1α, and PKA/CREB. These pathway findings help generate hypotheses, but they should not be presented as settled causal routes in humans. A signaling change in a cultured cell or injured animal is not equivalent to a proven treatment effect.

Does Red Light Therapy Help the Immune System?

Immune boost claim compared with evidence-based macrophage modulation

The phrase "immune boost" suggests that a stronger immune response is always better. Biology is more complicated. Excessive inflammation can damage tissue, while insufficient or mistimed inflammation can impair pathogen control and healing. The relevant question is whether an intervention produces an appropriate, measurable benefit in a defined condition—not whether it pushes immunity "up."

PBM may alter selected macrophage and cytokine signals under specific conditions. That is better described as possible immune modulation than immune amplification. It does not mean that red light therapy has been shown to increase generalized pathogen defense.

What 660 nm and 850 nm Can—and Cannot—Tell Us

The 630–670 nm red range and the 810–860 nm near-infrared range appear frequently in PBM research. Studies of macrophages have also used wavelengths such as 630, 660, 780, 808, 810, and others. However, wavelength alone cannot predict a macrophage response.

Near-infrared light may reach deeper tissue layers than visible red light in some settings, but penetration is not a fixed distance. It depends on skin and tissue composition, pigmentation, blood and water content, body site, beam geometry, spot size, surface irradiance, and the threshold used to define "penetration." Detecting photons at depth does not prove that a biologically effective dose reached the target.

Using 660 nm and 850 nm together may broaden spectral coverage, but the combination itself does not prove superior macrophage modulation. A 1:1 emitter count also does not guarantee equal optical output at the skin and is not a recognized clinical standard.

Why Dose, Timing, and Tissue State Matter

Research parameters needed to interpret PBM macrophage studies

Photobiomodulation outcomes can depend on interacting variables:

• wavelength and spectral bandwidth;
• irradiance at the treatment plane;
• radiant exposure;
• continuous-wave or pulsed output;
• pulse width, duty cycle, and frequency;
• distance, beam angle, spot size, and uniformity;
• cell type, tissue depth, pigmentation, and blood content;
• baseline inflammatory state;
• exposure schedule and the time at which markers are measured.

Radiant exposure is calculated as:

Radiant exposure (J/cm²) = irradiance (W/cm²) × time (seconds)

When irradiance is reported in mW/cm²:

Radiant exposure (J/cm²) = irradiance (mW/cm²) × time (seconds) ÷ 1000

For pulsed output, the calculation should use time-averaged irradiance or account for peak irradiance and duty cycle. A Hz value alone does not define dose. The calculated radiant exposure is the incident value at the measurement plane; it is not necessarily the amount absorbed by macrophages or by a target tissue.

Electrical wattage is not optical irradiance. Likewise, a study that used a tightly focused laser cannot be assumed equivalent to a broad LED field merely because both emitted the same wavelength. Study-to-study or study-to-device comparison requires the full optical and biological context.

Where Macrophage-Related PBM Research Is Concentrated

Evidence map for macrophage-related photobiomodulation research

Wound and tissue-repair research

Macrophages help coordinate the inflammatory, proliferative, and remodeling phases of repair. PBM has therefore been investigated in muscle injuries, oral ulcers, skin wounds, and other models. Some experiments report changes in macrophage markers alongside tissue-repair outcomes.

These findings cannot be generalized to every wound. Different wound types have different causes, microbial environments, blood supply, depths, and standard treatments. A result in an animal oral-ulcer model does not establish effectiveness for diabetic ulcers, burns, surgical wounds, or infected wounds in people.

Musculoskeletal and neurological injury models

Animal studies of muscle, nerve, and spinal-cord injury have reported macrophage or microglial changes after PBM. These models are useful for investigating mechanisms, but they often involve controlled injuries, precise optical parameters, and tissue sampling that cannot be reproduced in routine consumer use.

Chronic inflammatory and autoimmune-related conditions

Macrophages contribute to many inflammatory diseases, but that does not make macrophage modulation a proven treatment strategy for each condition. PBM research in one localized musculoskeletal or dermatological condition cannot be extrapolated into a claim that red light therapy "balances the immune system" throughout the body.

People with autoimmune disease should not change medication or disease-management plans based on a generalized macrophage article. Any clinical use must be evaluated for the specific diagnosis, device, intended use, and evidence base.

Active infection and systemic immune support

Macrophages play a role in pathogen defense, but current PBM evidence does not establish a general self-treatment protocol for viral or bacterial illness. There is no evidence-based rule to direct red light at the chest, throat, lymph nodes, thymus, lower back, kidneys, or adrenal region when someone feels sick.

Red light therapy is not an antiviral, antibiotic, vaccine, or substitute for diagnosis. It should never delay indicated or urgent medical care.

How to Judge the Evidence Quality

Researcher assessing PBM macrophage evidence quality

Most direct evidence on photobiomodulation effects on macrophages comes from cultured cells or animal models. These designs can reveal molecular changes and permit tissue sampling, but they cannot by themselves establish efficacy, safety, or a protocol for people.

When reading a macrophage study, ask:

1. What was studied? A cell line, primary human cells, an animal injury model, or patients?
2. What was measured? Gene expression, protein levels, surface markers, cell counts, phagocytosis, tissue healing, or a patient-important outcome?
3. When was it measured? A four-hour response may differ from a 24-hour or seven-day response.
4. What light parameters were reported? Wavelength alone is insufficient.
5. Was heat controlled? PBM is intended to act primarily through non-thermal mechanisms, but high irradiance, close exposure, or long duration can raise temperature.
6. Was there an appropriate sham or control group?
7. Was the result replicated independently?
8. Does the conclusion remain within the studied tissue, condition, and population?

The main evidence gaps include heterogeneous protocols, small sample sizes, limited human tissue data, inconsistent marker panels, short follow-up, and uncertain links between macrophage changes and clinically meaningful outcomes.

What Certifications and Registrations Do—and Do Not—Show

Manufacturing and compliance documentation can support process control and product-safety assessment, but it is not evidence that PBM changes macrophages or improves immune function.

• ISO 13485:2016 addresses a medical-device quality management system. It does not prove a macrophage or immune benefit.[8]
• FDA establishment registration identifies a registered establishment and may be associated with device listings. It does not mean that FDA approved, cleared, certified, or endorsed the establishment or every listed product.[9]
• CE marking indicates that the manufacturer has followed the applicable EU conformity route for the stated product and intended use. It is not an EU authority's clinical endorsement.[10]
• FCC documentation concerns applicable radiofrequency or electromagnetic requirements, not macrophage effects or clinical efficacy.
• IEC 62471 provides a framework for assessing photobiological hazards from lamps and lamp systems. It supports optical-safety evaluation, not treatment-effect claims.[11]

Compliance documents must be checked for current validity, model and configuration scope, intended use, and target market. They should never be used as substitutes for condition-specific clinical evidence.

Safety Considerations

PBM uses non-ionizing light and is often well tolerated when an appropriate device is used according to validated instructions. Safety still depends on optical output, exposure duration, body site, user characteristics, and design.

Important precautions include:

• do not stare directly into a high-intensity visible or near-infrared source;
• follow device-specific eye-protection instructions rather than assuming one type of eyewear covers every wavelength and risk group;
• stop use if unexpected heat, discomfort, persistent redness, or another adverse reaction occurs;
• review photosensitizing medicines or known photosensitivity with a qualified healthcare professional;
• seek professional guidance before use during pregnancy or near a known or suspected cancerous lesion;
• use caution over areas with reduced sensation because excessive heat may not be noticed promptly;
• do not apply a non-sterile consumer device to an open or infected wound unless it is specifically intended for that use and directed by a clinician.

The FDA's draft PBM guidance states that the long-term effects of prolonged non-thermal laser exposure are unknown and recommends warnings concerning pregnancy, cancerous lesions, misuse, eye safety, and areas without normal sensation.[1] Safety instructions must still be matched to the actual light source and intended use; draft guidance is not a universal treatment protocol.

Active illness, breathing difficulty, chest pain, high fever, confusion, dehydration, or rapidly worsening symptoms require appropriate medical assessment. PBM should not delay urgent care.

Key Takeaways

Photobiomodulation effects on macrophages are biologically plausible and supported by a growing body of cell and animal research. PBM can alter selected inflammatory mediators, metabolic signals, and macrophage-polarization markers under defined conditions.

The evidence is also highly parameter- and context-dependent. Macrophages do not operate as a simple M1/M2 switch, and a marker change does not automatically produce a clinical benefit. Direct human evidence remains limited, and there is no validated universal protocol for macrophage modulation, immune support, infection prevention, or treating someone who is sick.

Wavelengths such as 660 nm and 850 nm are relevant to red light therapy research, but wavelength alone cannot predict tissue dose or biological response. Responsible interpretation requires the complete optical parameters, biological model, timing, intended use, and evidence level.

FAQ

What are the main photobiomodulation effects on macrophages?

Laboratory and animal studies report parameter-dependent changes in cytokine expression, mitochondrial and redox signaling, calcium movement, phagocytosis, and macrophage activation markers. These findings do not establish a uniform effect in humans or a generalized immune benefit.

Does photobiomodulation shift macrophages from M1 to M2?

Some preclinical studies report fewer M1-like markers, more M2-like markers, or both at different stages after PBM. The M1/M2 model is simplified, and macrophage states form a continuum. It is more accurate to say that PBM may influence selected macrophage phenotypes under specific conditions.

Does red light therapy help the immune system?

PBM may modulate selected immune-related signals in certain experimental and clinical settings. It has not been shown to create a generalized immune boost, prevent infections, or increase overall pathogen defense in healthy users.

Is 660 nm or 850 nm better for macrophages?

There is no universally superior wavelength. Studies have used several red and near-infrared wavelengths with different doses, timing, and biological models. Tissue optics may favor near-infrared light for some deeper targets, but wavelength alone does not determine macrophage response or clinical value.

Where should red light be placed when someone is sick?

There is no evidence-based universal placement for systemic immune support or active illness. The chest, throat, lymph nodes, thymus, lower back, kidneys, and adrenal region should not be presented as standard self-treatment locations. PBM must not replace diagnosis, vaccination, antibiotics, antivirals, or other indicated care.

What happens if red light therapy is used every day?

The answer depends on the optical output, radiant exposure, treatment area, intended use, and user. Some research protocols use daily exposure, while others do not. Daily use is not universally safer or more effective, and the long-term effects of prolonged repeated exposure are not fully established for every light source and indication.

Can certifications prove macrophage or immune benefits?

No. ISO 13485, FDA establishment registration, CE marking, FCC documentation, and IEC 62471 address different quality-system, regulatory, electromagnetic, or optical-safety matters. They do not establish that a product changes macrophages or improves immunity.

References

1. U.S. Food and Drug Administration. Photobiomodulation (PBM) Devices—Premarket Notification [510(k)] Submissions: Draft Guidance for Industry and FDA Staff. 2023. https://www.fda.gov/media/164417/download
2. Ferreira VB, Sarmento JB, de Paoli F. Modulating macrophage polarization by photobiomodulation. Lasers in Medical Science. 2025;40:467. https://doi.org/10.1007/s10103-025-04717-z
3. Fernandes KPS, Souza NHC, Mesquita-Ferrari RA, et al. Photobiomodulation with 660-nm and 780-nm laser on activated J774 macrophage-like cells: effect on M1 inflammatory markers. Journal of Photochemistry and Photobiology B. 2015;153:344–351. https://doi.org/10.1016/j.jphotobiol.2015.10.015
4. de Brito Sousa K, Rodrigues MFSD, de Souza Santos D, et al. Differential expression of inflammatory and anti-inflammatory mediators by M1 and M2 macrophages after photobiomodulation with red or infrared lasers. Lasers in Medical Science. 2020;35(2):337–343. https://doi.org/10.1007/s10103-019-02817-1
5. Souza NHC, Mesquita-Ferrari RA, Rodrigues MFSD, et al. Photobiomodulation and different macrophages phenotypes during muscle tissue repair. Journal of Cellular and Molecular Medicine. 2018;22(10):4922–4934. https://doi.org/10.1111/jcmm.13757
6. Song JW, Li K, Liang ZW, et al. Low-level laser facilitates alternatively activated macrophage/microglia polarization and promotes functional recovery after crush spinal cord injury in rats. Scientific Reports. 2017;7:620. https://doi.org/10.1038/s41598-017-00553-6
7. Ryu HS, Lim NK, Padalhin AR, et al. Improved healing and macrophage polarization in oral ulcers treated with photobiomodulation (PBM). Lasers in Surgery and Medicine. 2022;54(4):600–610. https://doi.org/10.1002/lsm.23510
8. International Organization for Standardization. ISO 13485:2016—Medical devices—Quality management systems—Requirements for regulatory purposes. https://www.iso.org/standard/59752.html
9. U.S. Food and Drug Administration. Important Reminders About Registration and Listing. https://www.fda.gov/medical-devices/device-registration-and-listing/important-reminders-about-registration-and-listing
10. European Commission. CE Marking. https://single-market-economy.ec.europa.eu/single-market/goods/ce-marking_en
11. International Electrotechnical Commission. IEC 62471:2006—Photobiological safety of lamps and lamp systems. https://webstore.iec.ch/en/publication/7076