Can You Share Depression Through Saliva? New Study Explores Mood and Oral Bacteria in Couples

Key Takeaways

Oral bacteria may transfer between romantic partners and mirror changes in stress and mood.
Healthy spouses of depressed-insomniac partners developed similar oral microbiota and showed increased depression, anxiety, and cortisol levels.
However, cohabitation stress, not bacteria alone, may better explain these findings. Causality remains unproven.

Introduction: The Biology of Emotional Connection

Depressed Couple Could living with a depressed partner affect your mental health through more than just shared experiences? A recent study explores a provocative possibility: that oral bacteria exchanged between couples may help explain why moods seem to “sync” in close relationships.

While the idea that microbiota influence brain function isn’t new, applying this concept to emotional dynamics within couples introduces new questions—and demands a careful look at what the research truly supports.

What the Study Found

In a study published in Exploration of Research and Hypothesis in Medicine, researchers followed 268 newlywed couples over six months. In each pair, one partner had insomnia along with moderate depression and anxiety symptoms—a group the authors refer to as the “DA phenotype” (Rastmanesh et al., 2025).

Key findings included:

The healthy spouse’s oral microbiota shifted to resemble their partner’s.
They experienced higher depression and anxiety scores, based on validated psychological assessments.
Their salivary cortisol levels—a biological marker of stress—also rose.
These effects were more pronounced in women.

The researchers suggested that microbiota transmission through shared saliva (e.g., kissing or shared utensils) might influence these psychological changes.

Stress, Sleep, and the Oral-Gut-Brain Axis

While the study raises interesting hypotheses, it’s essential to recognize its limits. The findings are observational, meaning they show associations, not causality.

There’s a well-established biological mechanism that may better explain the results: chronic psychological stress. Living with a partner who is depressed or sleep-deprived can disrupt routines, impair sleep, and heighten emotional strain. These conditions are known to activate the hypothalamic-pituitary-adrenal (HPA) axis, increase cortisol, and trigger downstream effects on microbial communities.

A 2022 study by Paudel et al. in the Journal of Dental Sciences and Research demonstrated that psychological stress significantly alters both oral and gut microbiota, potentially influencing mental health through what researchers call the oral-gut-brain axis. (Paudel et al., 2022).

This suggests that microbial shifts may be a downstream effect of stress, rather than a root cause of depression.

Mood Synchrony or Emotional Contagion?

The study also touches on the phenomenon of “mood synchrony” between couples—a process supported by psychological research. Known as emotional contagion, this is the tendency for one partner’s emotional state to influence the other’s, often without conscious awareness.

Past research has shown that mood disturbances can propagate within households via subtle behavioral and verbal cues. This makes it difficult to isolate biological transmission from purely psychosocial mechanisms.

Long-term observational research has also found reciprocal emotional effects in couples over time, with one partner’s depressive symptoms influencing the other’s life satisfaction and vice versa (King et al., 2018).

Gender Differences: A Closer Look

One notable aspect of the study was that female partners experienced more pronounced changes in mental health scores and biological markers like cortisol. While briefly mentioned, this finding deserves more exploration.

Sociological and psychological literature suggest that women often carry greater emotional caregiving burdens in relationships. This dynamic, known as emotional labor, can amplify stress responses and increase vulnerability to mood disorders, independently of microbial exposure.

If Depression Can Spread… Why Not Happiness?

The idea of microbial “transmission” of depression leads to an important question: Why don’t we see the opposite effect? If dysbiosis (an imbalance in microbiota) can transfer between people, why isn’t there evidence that balanced, “healthy” microbiota transfer resilience or emotional stability?

There are two possibilities:

Dysbiosis may be more biologically impactful or transmissible than balanced flora.
These microbial changes are indicators, not drivers, of psychological states—meaning they mirror stress rather than cause it.

This distinction is key in interpreting results and designing future studies.

What This Means for Mental Health

The idea that oral microbiota might influence mood is biologically plausible, but the current evidence does not support a causal relationship. Instead, it appears more likely that emotional stress, poor sleep, and hormonal imbalance are primary forces, while microbiota shifts reflect those deeper disruptions.

Future studies, especially clinical trials targeting microbiota composition, may help clarify this link. But until then, it’s critical not to overstate what correlation implies.

FAQs

Can you really “catch” depression from your partner?
Not directly. You can’t catch depression like a cold, but your partner’s mood and bacteria may influence yours over time, especially if you’re under stress.
How would oral bacteria affect mood?
Some bacteria can influence inflammation and brain chemicals. If transferred through saliva, they might play a small role in mood changes.
Is stress more likely the cause than bacteria?
Yes. Stress, poor sleep, and emotional strain are more established causes of mood issues. Microbiota changes may just reflect those problems.
What is the oral-gut-brain axis?
It’s the connection between microbes in your mouth and gut, your nervous system, and your brain. Changes in one can affect the others.
How does stress affect microbiota?
Chronic stress raises cortisol, weakens immune defenses, and can shift your bacterial balance, both in the mouth and gut.
Why were women more affected in the study?
Likely due to emotional labor. Women often take on more caregiving roles, which can increase stress and emotional impact.
Can living with a happy partner boost your microbiota?
There’s no solid evidence yet. Dysbiosis (bad bacteria) may be easier to spread than beneficial microbes.
How are oral bacteria passed between partners?
Mostly through saliva—kissing, sharing food, or utensils. Couples often develop similar oral bacteria over time.
Do psychiatric medications mess with microbiota?
Some do. Antidepressants, antipsychotics, and others can alter gut and oral flora, though effects vary.
Can probiotics help with mood?
Some may help mildly. Strains like Lactobacillus and Bifidobacterium show promise, but they’re not a cure.
Does mouthwash help or hurt?
Used moderately, it helps. Overuse—especially strong antiseptics—can wipe out good bacteria too.
Should I worry about my partner’s microbiota?
Probably not. While early research shows some influence, the bigger factors are stress, sleep quality, and emotional dynamics. Microbiota may play a role, but it’s not yet clear how much.

Final Thoughts

This study encourages a fresh perspective on how emotional health may be shaped in close relationships. While the idea of microbiota playing a role in mood is intriguing, the more likely explanation remains psychological and environmental: living with a partner who is depressed, sleep-deprived, or emotionally dysregulated is inherently stressful. That alone can impair sleep, elevate cortisol, and worsen mood in the healthier partner, without any need for bacterial involvement.

The microbiota changes seen in the study may simply be a byproduct of close contact, such as kissing or sharing utensils. It’s possible that dysbiosis was passed through saliva, but had no direct impact on mood. In fact, what looks like “contagion” may just reflect the emotional toll of being in a high-stress household, not a biological transmission of depression.

Another overlooked factor is psychiatric medication. Many drugs used to treat depression and anxiety, like SSRIs, benzodiazepines, and antipsychotics, have been shown to disrupt the gut and oral microbiome. If one partner is medicated, that altered microbial profile could be transferred to the other during close contact. But again, that doesn’t mean the healthy partner becomes depressed. It just means they’re now hosting similar bacteria.

In short, shared stress, not shared saliva, is still the more plausible driver of mood changes. While the role of microbiota shouldn’t be dismissed entirely, its influence may be overstated. Future research should aim to separate biological coincidence from psychological cause, and focus more on how to protect mental health through better sleep, less stress, and more emotional support.

References

Rastmanesh, R., Vellingiri, B., Isacco, C. G., Sadeghinejad, A., & Daghnall, N. (2025). Oral microbiota transmission partially mediates depression and anxiety in newlywed couples. Exploration of Research and Hypothesis in Medicine, 10(2), 77–86. https://doi.org/10.14218/ERHM.2025.00013

David B King, Sarah L Canham, Rebecca J Cobb, Norm O’Rourke, Reciprocal Effects of Life Satisfaction and Depressive Symptoms Within Long-Wed Couples Over Time, The Journals of Gerontology: Series B, Volume 73, Issue 3, March 2018, Pages 363–371, https://doi.org/10.1093/geronb/gbv162

Paudel, D., Uehara, O., Giri, S., Yoshida, K., Morikawa, T., Kitagawa, T., … & Abiko, Y. (2022). Effect of psychological stress on the oral-gut microbiota and the potential oral-gut-brain axis. Journal of Dental Sciences and Research. https://doi.org/10.1016/j.jdsr.2022.11.003