The human body harbors a vast ecosystem of microorganisms, collectively known as the microbiome, which plays a critical role in health and disease. Recent research has uncovered a bidirectional link between the oral microbiome (the bacteria in the mouth) and the gut microbiome (the bacteria in the digestive tract), termed the oral-gut microbiome axis . This axis is influenced by various factors, including diet, lifestyle, and medical interventions. One emerging area of interest is photobiomodulation (PBM), a non-invasive therapy using low-intensity light to stimulate cellular activity. This article explores how PBM interacts with the oral-gut microbiome axis, its therapeutic potential, and the challenges ahead, based on three key studies .

What is Photobiomodulation (PBM)?

PBM, also called low-level light therapy, uses specific wavelengths of red or near-infrared light (typically 600–1000 nm) to penetrate tissues and activate molecules like cytochrome c oxidase in mitochondria. This process increases energy production (ATP), reduces inflammation, and promotes cell repair . Unlike laser surgery, PBM does not generate heat or damage tissues. It is already used clinically for wound healing, pain relief, and neurological conditions .

The Oral-Gut Microbiome Axis

The oral and gut microbiomes are interconnected through several pathways:

1. Direct Transfer: Oral bacteria can travel to the gut via swallowing, especially during dental procedures or poor oral hygiene . 
2. Immune Crosstalk: Infections or inflammation in the mouth (e.g., periodontitis) can trigger systemic immune responses that affect gut health . 
3. Metabolic Interactions: Bacterial metabolites (e.g., short-chain fatty acids) produced in the gut can influence oral bacteria, and vice versa .

Dysbiosis (imbalance) in either microbiome has been linked to diseases like obesity, diabetes, and inflammatory bowel disease (IBD) . For example, periodontitis is associated with an increased risk of gut inflammation and metabolic disorders . 

How PBM Influences the Microbiome

1. Direct Effects on Bacteria

PBM can alter bacterial behavior by:

• Disrupting DNA and Metabolism: Light energy may damage bacterial DNA or interfere with enzymes involved in metabolism. For instance, certain wavelengths (e.g., 660 nm) can reduce the growth of harmful oral bacteria like Porphyromonas gingivalis (a key periodontal pathogen) .
• Modulating Biofilms: Bacteria in biofilms (sticky communities) are more resistant to treatment. PBM has been shown to break down oral biofilms, making bacteria more vulnerable to antibiotics . 

2. Indirect Effects via Host Cells

PBM also acts through the body’s own cells:

• Reducing Inflammation: PBM suppresses pro-inflammatory cytokines (e.g., IL-1β, TNF-α) and activates anti-inflammatory pathways (e.g., NF-κB), which can restore microbial balance . 
• Enhancing Immune Function: PBM boosts the activity of immune cells like macrophages and T cells, helping the body fight infections and maintain a healthy microbiome .
• Improving Gut Barrier Function: Chronic inflammation weakens the gut lining, allowing harmful bacteria to enter the bloodstream. PBM strengthens the gut barrier by promoting tight junction proteins . 

Therapeutic Applications

1. Oral Health

• Periodontitis: PBM reduces gum inflammation and pocket depth by targeting P. gingivalis and other pathogens. In a case report, a patient with severe periodontitis treated with PBM showed significant improvement in gum health and a decrease in harmful oral bacteria .
• Oral Wounds: PBM accelerates healing in ulcers or after surgery by stimulating fibroblasts and reducing inflammation . 
• Dry Mouth: PBM can increase saliva production, which helps wash away harmful bacteria and maintain oral pH balance . 

2. Gut Health

• Inflammatory Bowel Disease (IBD): PBM reduces gut inflammation in animal models of IBD by restoring the balance between beneficial (e.g., Bacteroides) and harmful (e.g., Escherichia coli) bacteria . 
• Irritable Bowel Syndrome (IBS): PBM may alleviate IBS symptoms like abdominal pain and bloating by reducing gut permeability and modulating the immune system . 
• Neurodegenerative Diseases: Emerging evidence suggests PBM can improve gut microbiome diversity in Parkinson’s disease patients. A retrospective study found that 12 weeks of PBM treatment reduced the Firmicutes/Bacteroidetes (F/B) ratio (a marker of gut health) and increased anti-inflammatory bacteria like Bacteroides .

3. Systemic Health

• Metabolic Disorders: PBM may improve insulin sensitivity and reduce obesity by altering gut bacteria involved in fat metabolism . 
• Mental Health: The gut microbiome influences brain function via the gut-brain axis. PBM’s anti-inflammatory effects on the gut could help manage anxiety and depression . 

Challenges and Limitations

1. Dose Optimization: The optimal light wavelength, intensity, and duration vary depending on the target tissue and condition. For example, higher doses may be needed for deep tissues like the gut, while lower doses are sufficient for the mouth . 
2. Individual Variability: Microbiome composition differs widely between people, making it hard to predict how PBM will affect each patient. Genetic factors and lifestyle also play a role . 
3. Long-Term Safety: Most studies on PBM are short-term. Long-term effects on the microbiome and overall health remain unclear . 
4. Combination Therapies: PBM is often more effective when combined with other treatments, such as antibiotics or probiotics. However, the interactions between these therapies and PBM are not fully understood . 

Future Directions

• Personalized Medicine: Tailoring PBM protocols to an individual’s microbiome profile could enhance efficacy. 
• Wider Clinical Trials: Large-scale studies are needed to confirm PBM’s benefits in conditions like IBD and Parkinson’s disease. 
• Novel Devices: Portable PBM devices for home use could improve accessibility, but their safety and effectiveness require validation . 

Conclusion

Photobiomodulation offers a promising, non-invasive approach to modulate the oral-gut microbiome axis and treat a range of diseases. By directly targeting bacteria and indirectly enhancing host immunity, PBM has the potential to restore microbial balance and improve health. However, more research is needed to overcome challenges like dose optimization and individual variability. As our understanding grows, PBM may become a key tool in personalized microbiome-based therapies. 

References

1. Hakimiha N, Jahani Sherafat S, Laakso EL, Fekrazad R. Photobiomodulation and the oral-gut microbiome axis: therapeutic potential and challenges. Front Med (Lausanne). 2025 Apr 9;12:1555704. doi: 10.3389/fmed.2025.1555704. PMID: 40270495; PMCID: PMC12014685.

2. Liebert A, Bicknell B, Johnstone DM, Gordon LC, Kiat H, Hamblin MR. "Photobiomics": Can Light, Including Photobiomodulation, Alter the Microbiome? Photobiomodul Photomed Laser Surg. 2019 Nov;37(11):681-693. doi: 10.1089/photob.2019.4628. Epub 2019 Oct 9. PMID: 31596658; PMCID: PMC6859693.

3. Bicknell B, Laakso EL, Liebert A, Kiat H. Modifying the Microbiome as a Potential Mechanism of Photobiomodulation: A Case Report. Photobiomodul Photomed Laser Surg. 2022 Feb;40(2):88-97. doi: 10.1089/photob.2021.0057. Epub 2021 Dec 28. PMID: 34962422.