Researchers have discovered that patients with primary Sjögren's syndrome (pSS) have significantly altered oral bacteria compared to healthy individuals, with reduced microbial diversity that may serve as a distinctive marker of the disease. A comprehensive analysis of 21 studies involving 1,094 participants found consistent changes in the mouth's microbial community structure, suggesting oral dysbiosis (an imbalance of oral bacteria) could become an important diagnostic feature for this autoimmune condition.

What Is Sjögren's Syndrome and Why Does Mouth Health Matter?

Sjögren's syndrome is an autoimmune disorder in which the immune system attacks the glands that produce saliva and tears, leading to dry mouth and dry eyes. The condition affects roughly 1 in 1,500 Americans, though many cases go undiagnosed. Understanding what happens inside the mouth of people with this disease could help doctors identify it earlier and distinguish it from other autoimmune conditions like systemic lupus erythematosus (SLE).

Researchers conducted a systematic review and meta-analysis, examining data from nine medical databases through October 2024. The final analysis included 539 patients with primary Sjögren's syndrome and 555 control individuals without the condition. Most studies used advanced genetic sequencing methods (16S rRNA sequencing) to identify and catalog the bacteria present in oral samples.

What Specific Changes Did Researchers Find in the Oral Microbiome?

The study revealed several distinct patterns in how oral bacteria differ between people with Sjögren's syndrome and healthy controls. When researchers measured microbial richness, a key indicator of bacterial diversity, they found a significant reduction in patients with the condition. Specifically, the Chao1 index, which counts the total number of different bacterial species present, was substantially lower in people with Sjögren's syndrome compared to control groups.

Beyond just the number of different bacteria, the overall structure and composition of the oral microbial community was different. Ten of 15 studies examining community structure found significant differences between patients with Sjögren's syndrome and healthy individuals. The bacterial changes included:

• Increased Firmicutes: Higher levels of bacteria including Streptococcus, Veloncoccus, and Prevobacteria in people with Sjögren's syndrome
• Decreased Proteobacteria: Lower levels of Haemophilus parahaemophilus and Neisseria paraheemosa, bacteria normally found in healthy mouths
• Reduced Actinobacteria and Spirochaetes: Significant decreases in these bacterial groups that are typically present in oral health

These changes paint a picture of a fundamentally different oral environment in people with Sjögren's syndrome, one that could potentially be detected through testing.

How Could This Discovery Change Diagnosis and Treatment?

The significance of these findings lies in their potential clinical application. Currently, diagnosing Sjögren's syndrome can be challenging because symptoms overlap with other conditions and the disease develops gradually. If oral dysbiosis becomes recognized as a distinctive feature of the condition, it could offer doctors a new diagnostic tool. The research suggests that oral microbiome testing might help differentiate Sjögren's syndrome from other autoimmune diseases, potentially leading to faster and more accurate diagnoses.

The study authors concluded that "oral dysbiosis may serve as a distinctive feature of pSS compared to other autoimmune diseases like systemic lupus erythematosus." This distinction is important because it suggests the oral microbiome changes are not simply a general feature of autoimmune disease, but rather something specific to Sjögren's syndrome.

However, researchers acknowledged important limitations in their analysis. The studies included in the review could not determine whether the altered oral bacteria cause Sjögren's syndrome or whether the disease itself causes the bacterial changes. Additionally, most analyses focused on bacterial changes at the genus level, meaning researchers identified broad categories of bacteria rather than pinpointing exact species.

What's Next for Sjögren's Syndrome Research?

This meta-analysis, published in Rheumatology in April 2026, represents a significant step forward in understanding the biological mechanisms underlying Sjögren's syndrome. The research was conducted across multiple continents, with 57.1% of studies from Asia, 23.8% from Europe, and 19.0% from North America, suggesting the findings have broad geographic relevance.

Future research will likely focus on determining whether these oral microbiome changes could be used as a practical diagnostic test, and whether interventions targeting the oral microbiome might help manage Sjögren's syndrome symptoms. Understanding the relationship between oral bacteria and the immune system's attack on salivary glands could open new avenues for treatment beyond current symptom management approaches.