Red light therapy and gut health: the emerging science of photobiomics

Why the gut microbiome matters more than most people realise

The gut microbiome - the roughly 38 trillion bacteria, fungi, and other microorganisms living in your digestive tract - is one of the most researched topics in medicine over the past two decades. What started as niche gastroenterology has become one of the central frameworks through which scientists understand immunity, metabolism, mental health, and even brain disease.

The microbiome produces neurotransmitters (chemical messengers including serotonin and dopamine), short-chain fatty acids (SCFAs - small molecules that feed the gut lining and regulate inflammation throughout the body), and a range of metabolites that influence everything from insulin sensitivity to how well you sleep. It communicates with the brain via a bidirectional channel called the gut-brain axis - a network of nerve fibres, hormones, and immune signals that connects the gut to the central nervous system. Disruption of this ecosystem, called dysbiosis (a shift in the balance of gut bacteria away from healthy diversity towards a dominance of potentially harmful species), has been linked to conditions as varied as obesity, type 2 diabetes, inflammatory bowel disease, depression, and Parkinson's disease.

Given how central the microbiome is to health, the question of whether it can be influenced by red and near-infrared light is genuinely significant. And that is exactly what a new field of research - called photobiomics - is beginning to explore.

What is photobiomics?

The term "photobiomics" was coined in 2019 by a research group led by Dr Ann Liebert and Dr Brian Bicknell at the University of Sydney and Australian Catholic University, in collaboration with Dr Michael Hamblin (Wellman Center for Photomedicine, Massachusetts General Hospital - one of the world's most prominent photobiomodulation researchers). Their review paper, published in Photobiomodulation, Photomedicine, and Laser Surgery, introduced the concept: the combined effects of light on metabolic factors, the microbiome, and the interaction between the two.

The idea emerged from a straightforward observation. It was already established that photobiomodulation (PBM - the clinical term for red and near-infrared light therapy) has well-documented anti-inflammatory effects, improves mitochondrial function (the energy-producing machinery inside cells), and modulates immune signalling throughout the body. What the Liebert/Bicknell group asked was whether those systemic effects might extend to the gut microbiome - and if so, whether light applied to the abdomen could shift the composition of gut bacteria in a measurable way.

Their preliminary work in mice suggested the answer was yes. And as the field has developed since, a consistent picture has emerged across animal studies, a small number of human case reports, and retrospective analyses - though it is worth being clear about where the evidence stands: this is an emerging field, not an established one. There are no large randomised controlled trials in healthy humans yet. But what does exist is mechanistically credible and builds on solid foundations.

What the research actually shows

The evidence base for photobiomics builds from animal studies upward, with a growing body of human data adding weight to the picture. Here is what each layer shows.

The foundational animal study came from Bicknell et al. in 2018, published in Lasers in Medical Science. Mice had their abdomens irradiated with red (660 nm) or infrared (808 nm) laser - either as a single dose or multiple doses over two weeks. Genomic sequencing of their faecal samples showed significant differences in microbial diversity between PBM-treated and untreated mice (p<0.05). One genus of bacterium - Allobaculum, associated with a healthy gut microbiome in animal models - significantly increased after infrared (but not red light) treatment by day 14. The authors noted this was a preliminary trial, but it was the first direct demonstration that PBM could alter gut microbiome diversity.

Subsequent animal research has extended those findings. Reviews of animal model studies report that various PBM protocols have been associated with increases in bacteria strongly linked to gut health - including Akkermansia muciniphila (a bacterium that strengthens the gut lining and is often depleted in metabolic disease), Faecalibacterium prausnitzii (one of the most abundant and health-protective bacteria in a healthy human gut, with strong anti-inflammatory properties), and Roseburia (butyrate-producing bacteria that feed the colon lining) - though the precise wavelengths and protocols producing these effects vary across studies. A December 2025 study, using an 830 nm LED in a mouse colitis model (dextran sodium sulphate-induced colitis - a well-established laboratory model of ulcerative colitis), found that PBM significantly reduced inflammatory cell infiltration, crypt damage, and ulceration in the gut, while also modulating gut microbiota diversity and composition (p<0.05). A separate June 2025 in vitro study using human intestinal cells found that 635 nm light significantly reduced key markers of gut inflammation via the MAPK/NF-kB pathway - the same molecular switch that governs inflammatory signalling throughout the body.

On the human side, the evidence comes from case data and retrospective analyses - not yet from randomised controlled trials. The first published human case report (Bicknell et al. 2022, Photobiomodulation, Photomedicine, and Laser Surgery) documented microbiome changes in a single participant - a breast cancer patient who received PBM treatment (904 nm, applied to the abdomen, three times weekly for 11 weeks) as part of her care. Her microbiome was tested nine times across three phases: before treatment, after cancer therapy, and after PBM. The microbiome showed significant changes in diversity after PBM but not after cancer treatment alone, with an increase in known beneficial bacteria and a decrease in potentially pathogenic genera.

The most substantial human data comes from the Parkinson's disease research programme run by Liebert, Bicknell and colleagues. This matters for gut health because Parkinson's disease has a well-documented gut-brain axis component - many patients develop gut symptoms years before motor symptoms, and the microbiome of Parkinson's patients shows characteristic dysbiosis. A 2022 retrospective study (Bicknell et al., Journal of Personalized Medicine) analysed stool samples from Parkinson's patients who had undergone a 12-week PBM treatment programme - light applied to the abdomen, neck, head, and nose. The microbiome showed positive changes in the Firmicutes-to-Bacteroidetes ratio (the F:B ratio - a widely used proxy for gut health; a lower ratio generally indicates a healthier microbiome composition).

A January 2026 follow-up paper, published in the Journal of Clinical Medicine, extended this to five years - making it the longest published follow-up of microbiome changes in any PBM treatment programme. Six Parkinson's patients who had continued PBM therapy three times weekly for five years had their faecal samples analysed using 16S rDNA sequencing (a method of identifying bacterial species by their genetic fingerprint). Significant shifts in diversity were found over the five-year period. At the phylum level, Pseudomonadota (formerly Proteobacteria - a group frequently elevated in Parkinson's patients and associated with pro-inflammatory signalling) decreased in four of the six participants. Bifidobacteriaceae - a family of bacteria associated with beneficial gut function - increased in five of the six participants. The authors concluded that the parallel improvements in mobility and non-motor Parkinson's symptoms raised the hypothesis that PBM may interact with the gut-brain axis via the microbiome.

How light could plausibly affect gut bacteria

PBM does not directly kill or grow bacteria in the way that antibiotics or probiotics do. The proposed mechanism is indirect - light applied to the abdomen changes the local tissue environment in ways that favour a healthier microbial balance. Several pathways are proposed.

The primary mechanism is anti-inflammatory. Near-infrared light penetrates through the skin and abdominal wall to reach gut tissue, where it reduces the production of pro-inflammatory cytokines (signalling proteins that drive chronic inflammation) and downregulates NF-kB (nuclear factor kappa B - the central molecular switch that controls inflammatory gene expression throughout the body). Chronic gut inflammation is one of the main drivers of dysbiosis - it creates an environment in which pathogenic bacteria thrive at the expense of beneficial ones. By reducing that inflammatory state, PBM may create conditions in which the microbiome can rebalance.

The second mechanism involves mitochondrial function. Cytochrome c oxidase - the enzyme inside mitochondria that absorbs red and near-infrared light and converts it into cellular energy - is present not only in human cells but also in many bacteria. PBM may selectively stimulate certain bacterial species over others by influencing their energy-producing machinery, though this is more speculative and requires further investigation.

A third mechanism relates to the gut lining itself. PBM is known to support tissue repair and strengthen barrier integrity. The gut lining is a single-cell layer separating the gut contents from the bloodstream - when it is damaged or permeable (a state often called "leaky gut"), bacterial toxins called lipopolysaccharides (LPS) can cross into the bloodstream and trigger systemic inflammation. By supporting the health of that barrier, PBM may reduce the inflammatory signalling that dysregulates the microbiome in the first place.

A further indirect route has been proposed via the oral-gut microbiome axis. PBM has an established evidence base for conditions affecting the mouth - including oral mucositis (painful mouth sores associated with cancer treatment) and periodontal disease. Research into the oral-gut microbiome axis shows that oral dysbiosis can seed gut dysbiosis via swallowed bacteria. A 2025 perspective paper published in Frontiers in Medicine proposed that improving the oral microbiome through PBM may produce downstream gut benefits - an additional mechanism worth noting, though currently more hypothesis than demonstrated evidence.

The gut-brain axis: why this connects to far more than digestion

The significance of photobiomics extends well beyond gut symptoms. The microbiome's influence on health operates largely through the gut-brain axis - the bidirectional communication channel between the gut and the central nervous system, mediated by the vagus nerve (the longest nerve in the body, running from the brainstem to the abdomen and carrying signals in both directions), the immune system, and a wide range of hormones and metabolites.

Roughly 90% of the body's serotonin - the neurotransmitter most associated with mood regulation - is produced in the gut. Short-chain fatty acids produced by certain gut bacteria (particularly Faecalibacterium and Roseburia) feed the cells lining the colon, regulate immune responses, and have direct effects on brain function via the bloodstream. Gut bacteria also influence the production of GABA (gamma-aminobutyric acid - the brain's primary calming neurotransmitter) and dopamine precursors. This is why dysbiosis has been associated not only with gut symptoms but with conditions including depression, anxiety, cognitive decline, and neurodegenerative disease.

The Parkinson's disease research is particularly striking here. Parkinson's involves characteristic gut microbiome changes - reduced Faecalibacterium, increased pro-inflammatory Proteobacteria - that in some patients precede motor symptoms by years, suggesting the gut-brain axis may be involved in disease initiation and progression. The observation that PBM treatment appears to shift the Parkinson's microbiome towards a healthier composition, alongside clinical improvements in symptoms, raises an interesting hypothesis about how the gut-brain axis might be part of the mechanism through which PBM helps these patients.

What the evidence does and does not support

The honest summary of photobiomics research is this: the mechanistic case is compelling, the animal evidence is consistent, and the human data - while small in scale - points in the same direction. But there are no randomised controlled trials in healthy humans using gut health as the primary outcome measure. The world's first dedicated IBD clinical trial using PBM devices is understood to be underway in Australia, but results have not yet been published. This is an area where the science is ahead of the clinical trials, not the other way around.

What the evidence supports: red and near-infrared light applied to the abdomen can measurably shift gut microbiome composition in animal models, with consistent increases in beneficial bacteria and decreases in pro-inflammatory bacteria. Human case data from Parkinson's patients shows similar directional changes over treatment periods of 12 weeks to five years. The proposed mechanisms - reduced gut inflammation, improved barrier integrity, mitochondrial stimulation - are biologically credible and consistent with PBM's established effects in other tissues.

What the evidence does not support: specific claims about treating IBD, IBS, or other gut conditions in humans. The in vitro intestinal inflammation data and the mouse colitis studies are promising, but they are not human RCTs. The Parkinson's microbiome findings are from a specific and medically distinct population with a particular pattern of gut dysbiosis. Whether the same microbiome shifts occur in otherwise healthy people using PBM for general wellness is not yet known.

What this means in practice

The practical implication of the photobiomics research is that abdominal exposure during red and near-infrared light therapy sessions may have systemic effects that go beyond the surface-level benefits most people are aware of. Most NovaThera users position panels to expose the torso as part of a full-body protocol - the abdomen naturally receives exposure during standard sessions, delivering wavelengths across the 630-660 nm and 810-850 nm ranges used across the photobiomics research literature.

The systemic anti-inflammatory effects of full-body PBM are also relevant here. Chronic inflammation is one of the primary drivers of gut dysbiosis - and reducing overall inflammatory load throughout the body, rather than only targeting the gut directly, may create conditions in which the microbiome can shift towards a healthier balance. This connects the gut health angle to NovaThera's broader longevity and healthy aging research - chronic inflammation is the common thread running through most of the conditions where PBM has shown benefit.

It is also worth noting the connection to circadian rhythm regulation. Light is the primary regulator of the body's internal clock, and the gut microbiome has its own circadian rhythm - bacterial populations fluctuate over the 24-hour cycle in ways that are influenced by when and how much light exposure occurs. This adds another potential mechanism by which consistent light therapy practice might support microbiome health, over and above the direct anti-inflammatory and mitochondrial effects.

An emerging field worth watching

Photobiomics represents something rare in the wellness world: an emerging area of research where the science is genuinely ahead of the marketing. The term was coined by credible researchers at major institutions, the foundational work has been peer-reviewed and replicated in multiple animal models, and the human data - while preliminary - has been published in indexed journals with appropriate caveats about what it does and does not show.

The gut microbiome is one of the most consequential research areas in modern medicine. As its role in immunity, mental health, metabolic disease, and neurological conditions becomes clearer, interventions that can safely and non-invasively shift it towards healthier compositions will attract significant attention. PBM is not yet in that category for human gut health - but it is closer than most people realise, and the research programme underway suggests it is moving in that direction.

For anyone using red and near-infrared light therapy for other reasons - recovery, skin health, thyroid conditions, sleep, mood - the emerging photobiomics data suggests that abdominal exposure may be adding value that existing research frameworks have not yet fully captured. That is not a guarantee. But it is, at minimum, a reason to pay attention to this field over the coming years.