Maybe, as that fellow citizen singer of mine used to say, “you can't die of love”, but you can feel bad. At least according to a new study that points the finger at some unexpected culprits: mouth bacteria. Researchers from four countries monitored 268 newlywed couples for six months, finding that When one partner suffers from depression and anxiety, the oral microbiome of the other progressively changes, becoming more and more similar to that of the sick spouse.
The result? Even the initially healthy partner begins to develop depressive symptoms and sleep disturbances. We are not talking about emotional contagion or cohabitation stress: oral bacteria seem to have a direct role in altering the neurochemical balance, creating a real bacterial synchronization between spouses.
When Mouth Bacteria Become Messengers of Sadness
I study, published in Exploratory Research and Hypothesis in Medicine, involved research teams from Iran, India, Italy and the UK. Mouth bacteria are not only responsible for tooth decay and bad breath: they can directly influence our nervous system through what scientists call the “oral microbiota-brain axis”.
The mechanism is easily explained: through kisses and intimate contact, specific bacterial families such as Clostridia, Veillonella, Bacillus and Lachnospiraceae are transmitted from one partner to another. These mouth bacteria do not appear out of nowhere, however: Previous research has already linked them to brain disorders, depression and sleep problems.
Cortisol betrays microbial invasion
The researchers measured levels of salivary cortisol (the stress hormone) along with the composition of the oral microbiome. After six months of marriage, the initially healthy spouses showed significantly higher cortisol levels and worse scores on tests for depression, anxiety, and sleep quality. Interestingly, women seemed more susceptible to this “bacterial contagion.”
Neil Daghnall and his colleagues explain that mouth bacteria can compromise the blood-brain barrier or communicate directly with the brain through specific neural pathways. As we have already seen in studies on intestinal bacteria, the oral microbiome can also produce neuroactive substances that influence mood.
Beyond Mouth Bacteria: An Ecosystem That Speaks to the Brain
Our oral cavity hosts over 700 species of bacteria that form complex biofilms. When this delicate balance is disturbed (dysbiosis), pathogenic oral bacteria can prevail over beneficial strains, triggering inflammatory cascades that reach the brain.
Iranian research confirms what we already knew about microbiomes: There are no clear boundaries between oral and systemic health. Bacteria from the mouth can migrate to the intestines, lungs, heart and brain, carrying their metabolic effects with them.
Bacterial Marriage: When Love Synchronizes Even Microbes, But It Doesn't Convince Me 100%
The study has some limitations: It relies on self-reports to measure symptoms, does not control for factors such as shared diet or environmental stress, and the bacterial samples come only from tonsils and throat (I assume for economic reasons). However, the results are statistically robust and open up some fascinating possibilities.
Stanley Hazen of the Cleveland Clinic, an expert in cardiovascular microbiome, has demonstrated how other bacteria influence systemic diseases. Mouth bacteria appear to follow a similar logic: small microorganisms with big consequences.
The Era of Personalized Microbial Medicine
This discovery could revolutionize the therapeutic approach to mental illness in couples. If oral bacteria really mediate the transmission of anxiety and depression, targeted probiotics could become new therapeutic tools. Imagine: instead of resorting only to psychotropic drugs, we could “reset” the oral microbiome with personalized bacterial cocktails.
The message for couples is twofold: mental health is not just individual, but can have shared biological bases. Maintaining a balanced oral microbiome through proper hygiene and a healthy lifestyle could protect not only ourselves, but also those we love.
After all, if we are going to share everything in life, in health and in sickness, let's at least do it with the right mouth bacteria.
