Study links kissing to depression and anxiety

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Published Jun 08, 2025  •  Last updated 10 hours ago  •  2 minute read

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A new study out of Iran suggests that depression and anxiety might also be transmissible through kissing. Photo by iStock /GETTY IMAGESArticle content

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It’s no kiss of death, but a new study out of Iran suggests that depression and anxiety might also be transmissible through kissing.

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In the same way that such close contact can transmit infections like the common cold, mononucleaosis and herpes, so too can depression and anxiety be transmitted.

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The study says the depression and anxiety can trigger the release of the stress hormone cortisol, which can disrupt the delicate balance of bacteria in the mouth.

Research found that as many as 80 million bacteria are transferred in just one 10-second kiss.

The new study found that when one spouse had poor mental health and trouble sleeping, the healthy partner suffered similar symptoms after just six months. Bacteria were to blame.

“Specifically, in couples where one partner had (depression/anxiety), the oral microbiota of the healthy spouse mirrored that of the affected partner,” the researchers wrote in the Exploratory Research and Hypothesis in Medicine journal, per the New York Post.

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The research team followed 268 newlywed Iranian couples. One set of honeymooners reported struggling with depression, anxiety and sleep issues while their spouses were healthy at the start of the study.

Participants filled in surveys about their mental health and gave saliva samples for cortisol measurement and oral bacteria swabs for DNA analysis.

Researchers found that the healthy spouses, particularly women, had significant increases in depression, anxiety and sleep problems after six months. These symptoms weren’t as intense as their partners’.

Bacteria types including Clostridia, Veillonella, Bacillus and Lachnospiraceae were relatively abundant in the samples. Some species of these bacteria may be harmful to health.

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The researchers said there were several limitations to the study, including not taking into account underlying health issues and dietary factors that might influence oral bacteria.

They suggested exploring whether bacteria play a role in other mental and brain-related conditions.

Studies have identified other ways couples can be in sync, including heart rates, sleep patterns and even their stress and reproductive hormones.

For more health news and content around diseases, conditions, wellness, healthy living, drugs, treatments and more, head to Healthing.ca – a member of the Postmedia Network.

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