How kissing can actually spread depression and anxiety: study

Mental HealthHow kissing can actually spread depression and anxiety: studyBy Tracy SwartzPublishedJune 2, 2025, 6:00 a.m. ET

Baby got bac!

We all know that kissing and other close contact can transmit infections like the common cold, mononucleosis and herpes.

A new study out of Iran suggests that depression and anxiety might be transmissible through kissing, too.

transmissible through kissing. Photographee.eu – stock.adobe.com

Depression and anxiety can trigger the release of the stress hormone cortisol, which can disrupt the delicate balance of bacteria in the mouth.

Spouses can transfer this bacteria while smooching — in fact, prior research found that as many as 80 million bacteria are transferred in just one 10-second kiss.

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The authors of 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.

in the mouth. Tinnakorn – stock.adobe.comSee AlsoKissing could kill me: Men must follow three strict rules before we smooch because of this chronic condition

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

the study.

Participants completed surveys about their mental health and provided saliva samples for cortisol measurement and oral bacteria swabs for DNA analysis.

The researchers reported that the healthy spouses, particularly women, had significant increases in depression, anxiety and sleep difficulties after six months. These symptoms were not as

intense as their partners’.

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

research found that as many as 80 million bacteria are transferred in just one 10-second kiss. Alessandro Grandini – stock.adobe.com

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

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

Therapists and researchers have long recognized that a person’s mental health struggles can have a “ripple effect” on loved ones. This new study suggests that this impact is fueled in part

by harmful mouth bacteria.

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

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