Red Light Therapy and the Microbiome(s): Photobiomics
Red and Near-Infrared (NIR) Light Therapy has been shown to affect the human microbiome. Often in beneficial ways that can be utilized therapeutically.
A subset of light therapy science is now called Photobiomics. The application of light to modulate the various microbiomes of the body. This was highlighted in a 2019 review article by Ann Liebert and co-authors included Dr. Hamblin. [1]
Since 2019, we have watched the growing studies of microbiome research related to Red Light Therapy. Here we present our findings.
Not Just One Microbiome:
There are different microbiomes in distinct areas of the body. Most notably the gut, oral (mouth), skin, and genitalia microbiomes are currently considered distinct areas for Photobiomodulation treatments.
The gut microbiome not only affects digestion, but it known to affect metabolism, brain health, hormonal health, the immune system, inflammation and many other factors of health and disease. Interventions that improve the gut microbiome have been shown to improve health and reduce the severity of many diseases.
Other important microbiomes of the mouth and skin impacts diseases local to it, but also has systemic effects on the health of the entire body.
Diet affects the microbiome in many ways like with anti/pro-inflammatory foods, fiber, probiotics, and prebiotics. Factors like sleep, inflammation, exercise, stress, and obesity are also key areas to manage a healthy microbiome.
Often, this relationship is bi-directional for the factors listed above. [2] The cause-and-effect goes both ways. Does inflammation disturb the microbiome? Or does an unbalanced microbiome exacerbate inflammation? It is both.
So, is it correlation or causation? In this case it may not matter, as the correlation is so strong and consistent.
Background - Microbes: We Are Not Alone:
Humanity recently realized that we are not alone. Not out in the cosmos, but internally our bodies are a host to trillions of microbes.
Since these microbes are smaller than our cells, there are 10x more bacterial cells than humans cells in the body. Our gene count is outnumbered by over 100x to the bacteria within us. As explained in the below quotes.
"The bacterial cells harbored within the human gastrointestinal tract (GIT) outnumber the host’s cells by a factor of 10 and the genes encoded by the bacteria resident within the GIT outnumber their host’s genes by more than 100 times." [3]
"Metagenomic study of the human microbiome has demonstrated that there are 3.3 million unique genes in human gut, 150 times more genes than our own genome" [4]
Not only that, but the metabolic functions of the microbiome cause it to be referred to as a "second metabolic organ" due to the important energy processing it provides (the first metabolic organ being the liver). [5]
You may already be aware that the microbiome is often referred to as a "second brain" due to the important biological signals it produces for the body and the interactions it has with the brain. [6]
A microbe is any organism that is essentially invisible to the naked eye and must be viewed under a microscope. Such as bacteria. A biome is a distinct geographical habitat like a forest, jungle, or desert.
Thus, these bacteria form a symbiotic microscopic habitat called a microbiome.
This is unlike a parasitic relationship where the bacteria benefit at the detriment to the health of the host. In a symbiotic relationship the host also benefits from this relationship.
The most famous microbiome is in the gut (i.e. the intestinal tract). The basic function is that the microbes assist in the digestion of food. Similarly the roots of plants have a microbiome that also facilitate nutrient uptake.
But we also have unique microbiomes for the mouth, skin, blood, genitalia, and more.
Gut Frenzy:
For the past two decades, the relationship between the microbiome and human health has been a popular topic of research. Many known diseases and deficiencies are now correlated to gut health and the bacteria found within it. [7]
Aside from direct digestive issues, other notable areas are in metabolism (obesity and diabetes) and neurological issues (Parkinson's, Alzheimer's, and multiple sclerosis). [8]
Following close behind are probiotic products, powders, supplements, diet books, gut cleanses, and protocols that promise to support the microbiome. No longer are we doing healthy activities just for our own sake, but to take care of the little critters inside of us.
Bacteria and microbes have been vilified for over a century. Antibiotics revolutionized modern medicine, pasteurization improved the shelf-life of foods, sanitation systems reduced plagues, and basic hygiene reduced the spread of infections. [9]
Awareness and combat against the microscopic world has vastly improved the lifespan and longevity of humans.
However, like most things, too much emphasis on destroying bacteria has left an imbalance. Overly prescribed antibiotics can lead to gut dysbiosis, alcohol based mouthwashes disrupt the oral microbiome, overuse of hand sanitizer damages the skin microbiome, and chemicals in the food and water supply can further disrupt the microbiome.
As always, we must find a balance to manage the microscopic world within us. Many modern diseases are now strongly related to a compromised microbiome; from direct gut issues to hormonal issues to allergies, asthma, brain diseases, and inflammation.
PDT vs PBM - Light as Destroyer of Bacteria:
Light is well-known to affect bacteria and microbial behaviors. Light has natural antiseptic properties to surfaces, and has antibacterial properties when directly affecting microbes.
A well-lit area deters the growth of bacteria, molds, and fungus. A dark, damp, warm, enclosed area offer ideal conditions for microorganisms to flourish.
This is why light therapies have historically been used topically for skin conditions. Typically, shorter wavelength light has been used on the skin to hinder the bacteria that causes acne, disinfect wounds, kill toe fungus, and even have been used to treat antibiotic-resistant MRSA. [10][11]
However, caution must be used with short wavelengths like Blue/UV as they may also be disruptive to the "good" bacteria when used in situations that are not medically necessary. Like how we think of antibiotics, these wavelengths have no means of selecting only the "bad" bacteria and may wipe out good bacteria as well. As is explained more technically in the quote below:
"Blue light irradiation demonstrated bactericidal effects against black pigmented periodontal pathogens through endogenous porphyrin activation and reactive oxygen species generation. However, the same mechanism is unlikely to selectively target pathogenic taxa alone." [12]
When in an overgrowth, certain "bad" bacteria are black or colored so that they may absorb proportionally more of the light. So, blue light should not be used recklessly on areas such as the skin or mouth and only when a specific targeted bacterial treatment is necessary.
Remember that direct destruction of bacteria or cells with light is more under the category of PhotoDynamic Therapy (PDT), whereas Photobiomodulation (PBM) focuses more on the stimulation/inhibition of cells. As some articles remind us to be semantic and actually understand the definitions of these therapies.
"Direct microbial photobiological effects remain plausible but..." "should not be conflated with antimicrobial photodynamic therapy."[12]
So, the PDT actions of blue light on bacteria are outside the scope of this blog, as we will focus on the PBM actions primarily of the Red to Near-Infrared (NIR) range.
Red/NIR Light Mechanism for Modulating Microbiomes:
We know know that UV light has a direct effect on the skin microbiome. Further relaying benefits systemically into the body. There are now relations between the gut-brain-skin axis relating to melanin, light exposure, and microbial clocks. [13]
It is only relatively recently that science has turned it's attention to Red and NIR light therapy for affecting deeper microbiomes like the gut and mouth. These longer wavelengths are much less likely to cause direct microbial changes, but may lend energy towards less inflammation that promotes a better microbial balance.
A probiotic supplement or food is one containing (typically living) bacteria that is consumed into the digestive tract with the intent to "seed" these beneficial bacteria into the gut. Or, it is more likely that these probiotic foods will modulate the gut bacteria as it is passing though.
In contrast, it is clear that a light therapy treatment itself does not cause the spontaneous appearance of "good" bacteria. Nor does it directly attack "bad" bacteria. Rather, it is likely that light therapy creates the anti-inflammatory and signaling conditions that promote an internal re-balancing of bacteria in a positive direction.
This was discussed in a recent October 2026 review article of PBM on the oral microbiome.
"The strongest current rationale therefore supports a host-first model in which PBMT modifies epithelial integrity, inflammatory and redox signaling, tissue repair, and possibly salivary physiology, thereby changing the ecological conditions experienced by oral microorganisms."[14]
Many Red/NIR light therapy treatments are directed towards the mouth, gut, or skin. Thus, it may inadvertently affect those microbiomes.
As the 2026 review article on the oral microbiome indicates, often the treatment is used for something specific in the mouth like managing oral mucositis, and a secondary consideration is how it affects the microbiome.[14]
Luckily, most treatments on these areas show a positive shift in the related microbiomes, in addition to the normal benefits of the treatment. The microbiome explains an additional mechanism for the benefits and improvements seen from Red/NIR Light Therapy in those areas.
Treatments of Red and Near-Infrared light on the various microbiomes (gut, mouth, skin, etc) has shown promise towards improving related conditions and overall microbial health.
Practical Summary:
The application of Red/NIR light therapy on the skin, stomach (gut), mouth, and genitals have obvious benefits in their own right of anti-inflammatory, antioxidant, healing, and cellular protection. However, we can now appreciate that the alterations in those microbiomes may be playing a large role in these benefits.
The skin microbiome is an underappreciated area. The skin microbiome is related to skin conditions such as acne or flaking. Treatment of superficial wounds with light has a disinfecting effect, in addition to the improved wound healing. And we must consider there are skin microbiome connections to the inside of the body, especially as many consumer treatments are full-body.
Treating the abdomen/stomach area with Red/NIR light therapy positively affects the gut microbiome. This has direct clinical benefits for conditions related to gut dysbiosis such as several bowel disorders. More importantly, treating the gut has been studied to support systemic effects like immune health, muscle performance, and brain conditions.
The oral microbiome is another major area for treatments with Photobiomodulation. Again, direct treatments in the mouth are often intended to benefit the host such as for Oral Mucositis, bacterial issues in the mouth, dental/orthodontic applications, and reducing gum inflammation.
The oral microbiome is also closely connected to the gut. Treatments for the mouth can also improve the gut microbiome. As well, we know that supporting oral health has important systemic connections to the heart and brain. Chronically inflamed gums or mouth dysbiosis is often correlated to heart and brain issues.
We explore how supporting mouth health does not necessarily need specialized devices that go inside the mouth. Many successful oral treatments are through the cheeks or lips (extraoral), without needing the discomfort or contamination concerns of an intra-oral device.
Future research may be on other microbiomes such as the vagina, scalp, lungs, nasal cavity, home, or other areas of the skin.
So, for profound systemic benefits, treatments on the gut or mouth will modulate the microbiomes and offer benefits to many other important parts of the body.
Skin Microbiome and Red Light Therapy:
The microbiome starts with the skin. The skin is our barrier to the outside world, and some may be surprised that it is a host to it's own microbiome. This affects the integrity of the skin barrier itself. [15]
"The skin is the largest organ of the human body and provides multiple niches for colonization by diverse microbial communities, such as the stratum corneum, hair follicles, and sebaceous glands.21 Skin acts as the boundary between the external and internal environment of the human body, and the skin microbiome is an interface that contributes to human immunity." [16]
A disrupted skin microbiome is often correlated to skin conditions such as acne, eczema, psoriasis, and rosacea. [17]
Most research has focused on the effects of Blue and UV on the skin microbiome. These shorter wavelengths have a stronger effect particularly on the destruction of bacteria on the skin. Production of Vitamin D (from Ultraviolet light) also has an important effect on regulating the skin barrier and microbes, even deeper into the body. [18]
However, studies using just Red or Near-Infrared (NIR) light have been shown to improve these same skin conditions.
"Moreover, PBM light may be absorbed by local flora such as P. acnes, leading to the destruction of this bacteria [16]." [19]
The theory is that Red/NIR light does not affect the bacteria on the skin as strongly as blue. However, the anti-inflammatory modulation on the skin is sufficient to improve these skin conditions and modulate the microbiome in a positive way. [20]
Wound Healing and Sanitation:
Additionally, open wounds on the surface of the skin are greatly affected by the skin microbiome. Particularly, the concerns of infection from open wounds. It is well known that Photobiomodulation is well utilized to improve the speed and quality of wound healing. [21]
One study used 685nm red light on diabetic wounds infected with Staphylococcus aureus (S. aureus). The study showed that the light treatment reduced the bacterial load while also improving wound healing. [22]
One review article discussed how Red wavelengths from 630nm to 680nm may be ideal for managing skin bacteria of infected wounds.
"These wavelengths also cover absorption maxima of endogenous porphyrins generated by the vast majority of bacteria, including the most abundant Propionibacterium acnes and other resident skin propionibacteria, such as Propionibacterium granulosum, Propionibacterium avidum, and Propionibacterium humerusii,127 which may help in controlling the skin bacterial population and regulating the skin’s inflammatory response to aid in wound healing."[23]
Another study used several Red-NIR wavelengths to decontaminate open wounds on dogs. [24]
While studies of the skin microbiome have primarily focused on surface-level effects and wounds, we may find in the future how these skin microbes affect health deeper into the body.
And with many Red/NIR light therapy treatments often covering the entire surface of the skin with light (i.e. full body light therapy), this will be an important consideration as to how it is affecting the skin microbiome.
Red Light Therapy and Bowel Disorders:
Light therapy treatments of the stomach have the potential to directly manage diseases relating to gut dysbiosis and improve the microbiome. [25]
https://pubmed.ncbi.nlm.nih.gov/40270495/
The root "dys" meaning "bad" or "abnormal", and "biosis" relating to the biological mode of life. This term often refers to a deficiency or imbalance of the major types of bacteria found in a microbiome.
Major gut diseases such as inflammatory bowel disease, irritable bowel syndrome, and celiac diseases can now be characterized by the unique microbiomes compared to a "normal" or "healthy" gut. So, interventions that restore the "good" gut microbiome balance often will improve those conditions. This was highlighted in a 2023 review article looking at how PBM specifically intervenes with conditions relating to gut dysbiosis. [25]
A 2024 review article found 72 qualified studies used Photobiomodulation to manage a wide range of bowel diseases. They studied ulcerative colitis, inflammatory bowel, Crohn's disease, and more. Although the microbiome is not directly mentioned in this review, from the perspective we are musing from in this blog we cannot ignore that the microbiome played a big role. [26]
A 2022 study found that treating the spine increased the parasympathetic activity to improved control over bowel movements. [27] Showing that there are many systemic mechanisms for improving gut health with Red Light Therapy, and not necessarily needing direct penetration into the gut.
Treating the gut with Red Light Therapy will have many direct applications for bowel disorders, which often have hallmarks of a "bad" gut bacteria or microbiome balance.
Good Gut Bacteria Functions increase with Red Light Therapy:
Photobiomodulation has been found to be an effective intervention to shift the balance of "good" bacteria. Although we know that some of the "bad" bacteria are normal and essential, it is when the "bad" bacteria become unbalanced is where issues occur.
The quote below shows how Photobiomodulation (Red Light Therapy) treatments promotes an increase of several "good" bacteria in the gut.
"For example, PBMT was shown to increase the abundance of certain beneficial bacteria, such as Akkermansia, Faecalibacterium, and Roseburia and decrease the number of potentially pathogenic genera (54)." [25]
https://pmc.ncbi.nlm.nih.gov/articles/PMC10835098/
Two of the main phylum of bacteria are known as the Firmicutes and Bacteroidetes, and their ratio is an important indicator of gut health. One study using PBM on Parkinson's patients demonstrated a positive shift in this ratio:
"Liebert Ann and Bicknell and their co-workers showed that the PBM therapy (delivered to the head, nose, neck and abdomen) can diminish a range of clinical symptoms of Parkinson’s disease and affect the gut microbiome composition. Their research showed positive changes in the Firmicutes to Bacteroidetes (F: B) ratio in these patients (52). "[25]
Another 2023 review article of the bi-directional relationship between Parkinson's disease and gut health also remark on studies confirming the positive change in the F:B ratio. [28]
A large 2024 review of PBM for Parkinson's disease also places emphasis on the treatment target of the gut-brain axis. [29]
An important metabolite of a healthy microbiome is butyrate, a short-chained fatty acid. While this fat can be found in butter, it is more important that there are indicators that it is produced within the gut itself by the microbiome as it processes food. A 2023 article calls butyrate production a "sentinel" (meaning protector) of the gut as it protects the gut lining, protects against inflammation, and of course protects against all the downstream issues of gut dysbiosis. [30]
Yes, a recent 2025 study applying Photobiomodulation to the gut of Alzheimer's patients found an increased level of butyrate production as well as several other functions of the gut.
"Notably, gm-PBM specifically enriched short-chain fatty acid-producing bacteria, elevated propionate, butyrate, and secondary bile acids, and restored intestinal barrier integrity, whereas tc-PBM induced minimal microbiota changes." [31]
A 2025 study showed several major gut shifts with the Photobiomodulation treatments. And may support the gut microbiome even after disruption by heavy exercise.
"Abdominal PBMT maintains seven major gut phyla disrupted by intense exercise, enriches SCFA-producing taxa, reduces pathobionts, and elevates circulating and fecal butyrate, spermidine, L-carnitine, and acetylL-carnitine (all P ≤ 0.0001)."[32]
One 2021 case study used PBM on the abdomen of a patient as they underwent therapy for breast cancer. They found increases in the beneficial bacteria in the microbiome monitoring. There were 3 treatments per week over 11 weeks. [33]
Thus, Photobiomodulation treatments appear to positively modulate every important aspect of the gut microbiome. This offers a promising clinical mechanism to help manage these gut diseases. It comes as no surprise that applying Red Light Therapy to the abdomen will be an important treatment in the future for many disease and health management.
A popular article also notes that the intracellular melatonin production from NIR treatments will also improve gut health. Overall, the reduced inflammation and antioxidant properties of Red/NIR light will provide a more favorable environment for the "good" bacteria to flourish. [34]
Gut Treatments increase Muscular Metabolism:
Aside from direct bowel diseases, Photobiomodulation treatments of the gut can reduce systemic inflammation and improve metabolism.
Remarkably, one 2025 study treated the abdomen and improved muscle endurance by modulating the gut microbiome.[35]
As we know the gut microbiome affects metabolism in positive ways. So if we want to boost muscle growth with Red Light Therapy, we can consider treating the gut in addition to the muscle groups directly.
Red Light Therapy and the Immune System:
A massive 2021 review article gives an excellent history and background of the gut microbiome leading up to the usage of Photobiomodulation to improve it. They draw upon the immune health improvements from gut treatments, and protection of the lung microbiome. Which, they make an important recommendation to use Red/NIR light therapy for respiratory illnesses and COVID19, which was still a major issue at that time. [36]
For example, the famous 2022 study on COVID patients used a LED wrap around the abdomen/chest and reduced the severity of the illness. Although the study didn't directly measure the microbiome, we must consider treatments like this will benefit from the gut microbiome changes. In addition to the potential of direct cytokine modulation and improving lung function. [37]
Additionally, review articles have shown many studies of the benefits of Photobiomodulation on Asthma, Allergies, and COPD. [38][39][40]
We know that these issues are often related to the microbiomes [41][42], so it would not be surprising if future Photobiomodulation studies start monitoring and attributing the mechanisms to microbial changes during treatment, particularly for the immune system, respiratory issues, and lung function.
So, we already have remarkable systemic connections that treatments to the gut microbiome can improve muscle performance, the immune system, and lung microbiota.
But these profound benefits isn't what PBM is known for in this topic.
The Gut-Brain Axis with PBM
Using Photobiomodulation to affect the Gut-Brain axis is one of the most promising techniques in clinical research. As has been well established is the connection of the microbiome to the brain.
One article notes that treating a Central Nervous System (CNS) disorder may include gut treatments, in addition or alternative to treating the head/brain directly:
"Recently, PBM applications have expanded beyond traditional CNS irradiation, demonstrating potential in various areas, particularly brain–gut axis intervention and enhancing blood–brain barrier (BBB) permeability. (1) PBM modulates interactions between the nervous system and gut microbiota, improving mood and cognitive function (Huang et al. 2024)." [43]
Thus, an important compliment to Brain RLT treatments such as for Parkinson's and Alzheimer's will not only treat the head, but will also treat the abdomen to affect the gut-brain connection.
This was specifically called out in a August 2025 review of PBM for Brain health:
"Another theory pertains to brain-gut targets. Some studies combined bPBM and transabdominal PBM [[25], [26], [27]], to target the microbiome-gut-brain axis, which is crucial in the pathophysiology of both AD and PD [28]. This approach could leverage the brain-gut connection to amplify therapeutic effects. These remote approaches open new possibilities for PBM therapy, potentially overcoming the limitations of light penetration through the skull in transcranial bPBM." [44]
A December 2025 review article reports specifically on the benefits of Abdominal Photobiomodulation for brain conditions.
"Human trials, mainly in Parkinson’s and Alzheimer’s disease, used 630–904 nm light and reported gains in mobility, balance, cognition, and olfaction" [45]
Red Light Therapy treatments of the gut are a powerful way to create a combination of systemic effects and direct effects.
Now being incorporated into red light therapy brain health protocols to treat the gut. However, it seems that most conditions can be improved systemically through these gut treatments.
Insufficient Stomach Penetration with Red/NIR Light Therapy
It is doubtful that a significant amount of photons directly reach the stomach or intestines with transabdominal treatments.
Like with many PBM treatments, it is likely that the superficial absorption of photons on the abdomen has systemic and bystander effects that reduce inflammation in the gut. Thereby promoting a better microbiome balance.
As explained by Dr. Hamblin in one interview:
"I don't know how much of the light gets to the intestines when you put it on the belly, that's the thing, there is the skin, the muscle, and what can be quite a considerable layer of fat in the belly. And then you've got the guts which are all wrapped around each other. So I doubt that much light actually gets to the gut... some will, but I think overlying tissue is what absorbs the light, right, the skin, the muscle, and the fat. And they all respond to Photobiomodulation. And almost certainly by reducing inflammation. It's well known that the fat is a major source of systemic inflammation and by changing the mitochondrial metabolism, you can switch cells from M1 to M2..." - Dr. Hamblin [Neuronic YouTube Channel, ~50min]
A recent 2025 article on PBM affecting the Gut-Oral microbiome also expresses the same conclusion:
"Even with optimized near-infrared (NIR) wavelengths (typically in the 760–1,500 nm range, where penetration is maximized), absorption and scattering by these tissues greatly reduce the effective light dose reaching the deeper layers. " [46]
As the quote above makes clear, transcutaneous (through-the-skin) Red/NIR Light Therapy treatments on the abdomen does not directly reach the gut organs such as the stomach or intestines. This is due to exponential absorption and scattering losses through the skin and fat layers.
Thus, improvements to the gut from abdominal treatments are likely through superficial absorption that leads to systemic and bystander mechanisms.
A recent 2026 case study used Photobiomodulation on the head and gut on a 6 year old patient with autism. They also tested positive the before and after microbiome changes from the fecal matter. The caregiver reported positive shifts in bowel movements, more stable mood, reduced irritability, and improved communications. [47]
The mechanistic discussion is the same, that there are host-level changes (i.e. reduced inflammation) that affect the microbiome, as targeting the intensities directly is not feasible.
"These host-level changes could alter the ecological conditions that shape microbial composition. In this model, the microbiome is not necessarily a direct photonic target, but rather a downstream biological readout of changes in the intestinal niche (Guimarães et al., 2025)." [47]
This is an important consideration for many PBM treatments. We treat the abdomen to improve the gut microbiome, yet an insufficient amount of photons actually reach the gut. The gut benefits are from superficial photon absorption that reduce inflammation to create a more favorable environment for the microbiome.
Meanwhile, many influencers and brands insist that you need direct, deep penetration treatments for Red Light Therapy to be effective. Despite consulting directly with Dr. Hamblin for their sales narratives, influencers are very dismissive of Dr. Hamblin's preference for low intensities, proper exposure time, and systemic mechanisms. As it is more profitable to claim that "high" intensities penetrate deeper for direct benefits, despite the obvious risks influencers are willing to put onto their followers.
Oral Microbiome connects to the Gut Microbiome
The 2025 gut-oral PBM review article proposes that treatments of the oral cavity (mouth) may be a promising alternative to improve the gut microbiome. [46]
There is a strong connection between the oral and gut microbiomes, modulating one would likely affect the other. Treatments inside the mouth or through the cheeks may be a promising avenue to improve the gut microbiome and systemic health.
"The oral cavity contains a diverse and intricate microbial community that continuously migrates to the gut through swallowing, creating a dynamic relationship between the oral and gut microbiomes"[46]
Thus, we have another avenue for affecting the gut microbiome by treating through the mouth and oral cavity. In addition to the direct treatments on the stomach, despite their acknowledged limited penetration.
Ironically, treating the mouth with PBM may have a more direct effect on the gut microbiome than on the abdomen itself.
Oral Microbiome Split-Mouth Study
A 2026 study treated only one side of the mouth and left the opposite side of the mouth as a "split-face" control. Yet, after the treatment they showed no significant difference between the two sides of the mouth. This likely because saliva can still transfer from one side of the mouth to the other and equilibrate the microbiome inside the mouth.
"This biological interconnectivity is particularly critical for microbiome outcomes, as microbial communities can equilibrate and disperse rapidly throughout the oral cavity. Consequently, the null findings observed in our study could partly reflect this carry-over effect, which may have masked true localized differences. Conversely, any positive compositional changes identified in the placebo or PBM quadrants might reflect indirect, systemic or mouth-wide ecological shifts rather than direct, localized actions of PBM."[48]
This further supports that treatments into the mouth can affect the bacterial mucosa that can lead to other parts of the digestive tract.
Oral Inflammation Treatments:
A rapidly studied area is the application of Red/NIR Light Therapy to benefit the oral cavity (the mouth). Dentists can use it to manage pain and healing after procedures such as tooth extraction or even speed up the rate of orthodontics (braces/Invisalign). [49][50]
PBM is of particular usage for the treatment of Oral Mucositis. This is the painful inflammatory issue often caused as a side effect of chemotherapy cancer treatments. Since there are limited effective treatments for this condition, PBM has the best path to be approved for it. Studies on Oral Mucositis often have the opportunity to monitor the oral microbiome, as this one did. [51]
A new October 2026 article directly covers the oral microbiome as it may be disrupted during cancer treatments, and how Photobiomodulation plays a role in protecting and restoring the oral microbiome through those procedures. Again, they emphasize that the effects of Red/NIR on the microbiome are a host-level effect and hardly through direct modulation of the bacteria themselves. [14]
Treating the mouth and oral cavity with PBM can have numerous direct benefits. For example reduced gum inflammation, managing periodontal diseases, reducing pain, and managing pathogenic bacteria. [52] Naturally, many of these benefits may also be related to the oral microbiome.
A 2024 study showed that both Red and NIR light were able to protect the oral microbiome particularly through upregulation of human gingival keratinocytes.
"Our data demonstrated that LED pretreatment on microbially challenged HGKs with specific continuous wavelengths (red: 615 nm; near-infrared: 880 nm) induced the production of various antimicrobial peptides, enhanced cell viability and proliferation, promoted reactive oxygen species scavenging, and down-modulated proinflammatory activity." [53]
One study monitored the saliva for bacterial risk factors for dental caries (cavities) after PBM treatment with either Red-NIR 625nm-850nm LED light or a broad spectrum light. Both light treatments reduced the bacterial risk factors as measured in the saliva. [54]
Oral Microbiome Systemic Effects:
An excellent 2025 review article focused specifically on reviewing the Photobiomodulation studies relating to improving oral dysbiosis. A disrupted oral microbiome has many systemic effects on the body, as well as downstream gut and gastrointestinal effects. Thus, the antimicrobial effects of light in the mouth hold great potential to manage issues related to oral dysbiosis.[52]
Moreover, we are often told by our dentists that there is a connection between oral inflammation and heart health. Which they believe is a stronger motivation to get us to floss between visits. The dentists are not just lazy for wanting to scrape less plaque from your teeth, as the studies do report that chronic oral infections can also affect the brain such as in Alzheimer’s and Parkinson’s diseases. [46]
An excellent 2022 review article covers the gut and oral microbiome research with PBM up to that point. Of note, they also explain the indirect effects of reducing inflammation and promoting healthy saliva production may be the reason for PBM's effects on the oral microbiome. [55]
"It is important to note that the indirect effect of PBM should also be considered. For example, saliva plays a pivotal role in maintaining a healthy oral cavity and promotes the natural beneficial relationship between the oral microbiota and the host [135]."[55]
Similar to the gut, there is much more to oral PBM treatments than just benefits inside the mouth. The downstream effects to other microbiomes and systemic effects from the mouth to the heart and brain cannot be ignored.
Treatment Options: Inside or Outside the Mouth?
A complexity with Oral Photobiomodulation is the option to treat inside or outside of the mouth. An option that we generally don't have with gut microbiome treatments, as we must treat through the abdomen and just hope for the best.
Thus, an outpouring of intra-oral (inside the mouth) Red Light Devices have flooded the market. The traditional method would be to use a narrow laser or torch, or use a fiber-optic attachment to reach the light inside the mouth to target the light inside the mouth.
However, now consumer products have these "mouth-guards" that line the inside with LEDs [56][57], a clear plastic "lollypop" with LEDs inside to hold inside the mouth, or even LED toothbrush heads that give you Red Light Therapy while you brush your teeth.
Despite the claims of these devices being medical grade, be wary of consumer grade devices using plastic inside the body, as they should be tested for leachability - the plastic leeching into liquids such as the saliva or mucosa that are in contact with it.
The other alternative, often not presented by influencers and brands trying to push novel intra-oral devices, is simply extra-oral treatments. As the prefix "extra" implies, this is treatments outside the mouth. For example, simply shining the light on the cheeks or outside of the mouth over the lips. Sometimes simply called transcutaneous treatment, as like most PBM treatments, it is treatment with intent to get through the skin.
This is an important question for the clinical treatments of oral mucositis. Treatments are often intraoral, however, a much more convenient and comfortable treatment would be extraoral treatments. Remember, the burning pain is often on the tongue, although it also occurs on the insides of the cheeks.
Many studies and articles have confirmed that extraoral treatments are similarly effective as intraoral treatments for oral mucositis.
Penetration through the the cheeks to the inner mouth has been modeled in some studies. [63][64]
The advantages of Extraoral treatments are clearly outlined in a 2026 study:
"Extraoral (EO) PBMT is non-invasive, requiring no mouth opening or mucosal contact, reducing discomfort and infection risk [14–16], while enabling irradiation of oropharyngeal regions and, with multi-beam devices, shorter application times [16, 17]. Intraoral (IO) PBMT, in contrast, requires multiple application points and greater cooperation, making it more technique-sensitive and less feasible in pediatric practice [18]." [58]
Any loss in efficacy is compensated for by dose and is further approved by caregivers and patients as the more convenient, compliant, less painful, more sanitary, and more comfortable treatment option.
"These findings suggest that while intraoral PBM may offer superior localized effects, extraoral PBM remains a promising alternative, particularly when intraoral application is not feasible."[61]
So, we can infer from this research that supporting the oral microbiome and inflammation can be similarly achieved through extraoral treatments. Particularly much less severe cases if we just want to improve the overall health of our mouth, then it is not worth the additional risks and complexity of an intraoral device.
This means most people can improve their gum, teeth, and mouth health with the LED Panels treatments on the cheeks, mouth, and neck. Without needing any fancy intraoral devices save for actual medical necessity that can accept the additional risks of those internal devices.
PBM and the Vagina Microbiome:
The vaginal microbiome is considered the first inoculation of a baby with starting their own microbiome. Like the gut, it can be affected by many of the same factors of diet, stress, and lifestyle factors. As well as many hormonal factors and hygiene. [65]
Dysbiosis may manifest as candida (yeast) overgrowth and other bacterial infections. If chronic, may lead to reproductive issues or other health complications. [66] And we cannot ignore that the gut microbiome also affects this microbiome.
Treatments of Photobiomodulation on/in the vagina are gaining popularity, for example treating pelvic floor pain or conditions related to menopause. [67][68]
A 2023 review article considers the effect of Photobiomodulation on the vagina microbiome. While mostly theoretical without any direct studies on this topic, it makes connections to the gut-vagina axis and the effects of PBM on other microbiomes. With one study used water-filtered IRA (broad spectrum NIR light) to manage Chlamydia bacteria in-vitro. [69]
So, we have yet another major microbiome to consider with these popular new Photobiomodulation treatments.
Sunlight and the Microbiome:
With so many factors affecting the microbiome, there is no surprise that sunlight would affect it as well. Even skin exposure to sunlight is correlated with positive changes to the gut microbiome. [70]
Some food allergies may also be related to gut dysbiosis and a malfunctioning immune system. One study used full spectrum light to reduce diarrhea related to food allergies. [71] As we mentioned near the beginning, the gut microbiome also has a powerful effect on the immune system, and that includes food and seasonal allergies.
Other Microbiome Areas for PBM Research:
There are many other microbiomes that may be of interest in the future for Photobiomodulation. We discussed some of the most popular microbiomes, which naturally has been explored by the clinical literature. However, we hope to see more in the future.
Nasal Microbiome: Intranasal Photobiomodulation applications insert a small diode (Laser or LED) into the nostril(s). This is typically a brain, allergy/sinus, or systemic (blood) treatment. Considering the nasal microbiome may be another interesting area for PBM research.
Lung Microbiome: PBM Treatments over the lungs will be important for respiratory health and immune function. Monitoring the lung microbiome may be challenging, but also an interesting consideration for mechanisms.
Scalp Microbiome: Research into the microbiome of the scalp is becoming popular for it's relationship to hair loss and dandruff (flakes). [72] Popular Photobiomodulation treatments treat the scalp with helmets marketed for hair loss or brain health. Testing the microbiome changes in the scalp during these studies may give an interesting insight into the mechanisms that PBM is affecting.
https://pmc.ncbi.nlm.nih.gov/articles/PMC13478509/
Home/Room Microbiome: Yes, our homes are host to microbiomes in the air, dust, and moist areas. Often made obvious when there is mold overgrowth or unwanted bacteria in the home. With many Red Light Therapy devices being excessively large and shining light into the entire room, they are likely affecting the microbiome of the room itself.
Conclusions:
The microbiome is an important area to consider when managing health and biohacking. There are many studies and peer-reviewed articles over the past 2 decades focused on how the microbiome affects human health. This is made apparent to consumers by many diets, probiotics, prebiotics, and protocols that promise to support the gut bacteria as a proxy for improving health.
Light has natural and obvious effects on bacteria, particularly on managing "bad" bacteria in the mouth, gut, skin, and other areas.
Longer wavelength light like Red-NIR likely have more indirect effects. Often improving the inflammation on the host, which leads to more favorable conditions in the balance of "good" bacteria.
Considering the gut-brain axis is a major consideration for brain conditions such as Parkinson's and Alzheimer's and other Central Nervous System disorders. However, it is clear that abdominal PBM treatments can benefit the immune system, respiratory health, allergies, metabolism, and even muscle performance.
Monitoring the microbiome will help explain many of the systemic mechanisms for how Photobiomodulation works in many parts of the body, even when many PBM studies don't consider the effects on the microbiome yet.
Remember, we must appreciate that Red/NIR light therapy may not directly penetrate all the way through the abdomen and actually reach the actual "gut" organs such as the intestines or stomach. However, treatments on the abdomen have been proven to work on the gut microbiome through host-level mechanisms.
Alternative treatment routes may be through the mouth, which also has may of the same benefits in it own right. And treatments can be done through the cheeks or lips, and not necessarily need to have devices go inside the mouth.
Many other microbiomes may be of interest with PBM in the future, such as the vaginal microbiome, scalp, nasal, and lungs. But we do have a lot of information to understand that light does affect these areas, likely in positive ways that promote the benefits that we are already observing in those areas.
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