Kissing is often seen as a romantic gesture, a way to express affection, or even a test of compatibility.
But beneath the surface of this intimate act lies something far more fascinating—a microscopic world teeming with life.
Scientists in the Netherlands have discovered that a single 10-second kiss can transfer up to 80 million bacteria between partners.
And if you and your significant other kiss frequently—around nine times a day—you likely share eerily similar oral microbiomes.
A Walking Microbial Ecosystem
Our bodies are home to more than 100 trillion microorganisms, forming a diverse and intricate ecosystem that plays a crucial role in digestion, immunity, and overall health.
We don’t just coexist with these microbes—we depend on them.
According to Jeffrey Gordon, a biologist at Washington University, “We think that there are 10 times more microbial cells on and in our bodies than human cells.
That means that we’re 90% microbial and only 10% human.”
In other words, humans aren’t just individuals—we’re colonies.
Much like the Portuguese man-o’-war, a marine organism that consists of multiple symbiotic entities working together, our bodies function as an amalgamation of human and microbial parts.
Nowhere is this more evident than in our mouths, which house over 700 varieties of bacteria.
While factors like genetics, diet, and age shape our oral microbiome, new research reveals that the people we kiss also play a significant role in shaping our bacterial communities.
What the Science Says
Researchers from the Netherlands Organisation for Applied Scientific Research (TNO) conducted a study involving 21 couples, asking them about their kissing habits—how often they kissed daily and for how long.
To investigate microbial similarities, the team collected samples from the participants’ tongues and saliva.
Their findings, published in the journal Microbiome, revealed that couples who kissed at least nine times per day had strikingly similar oral bacterial communities.
But just how much bacterial swapping happens in a single kiss?
To measure this, researchers had one partner consume a probiotic drink containing well-known bacteria like Lactobacillus and Bifidobacteria, then share a controlled kiss with their partner.
The result? An estimated 80 million bacteria were exchanged in just one 10-second kiss.
Wait, Isn’t Saliva Full of Germs?
Here’s where things get interesting.
We tend to think of bacteria as harmful, something to avoid.
But the reality is far more complex.
Most bacteria in our mouths are beneficial, playing a critical role in breaking down food, preventing infections, and even influencing our immune responses.
The idea that kissing is “dirty” is a misconception. In fact, the constant exchange of microbes may actually help strengthen the immune system by exposing the body to diverse bacterial strains.
This microbial sharing can help partners develop a more robust and balanced oral microbiome.
The Hidden Benefits of Kissing
Beyond the obvious romantic and emotional connection, science suggests that kissing has additional perks:
- Boosts Immunity: Exposure to diverse bacteria can train the immune system to recognize and fight off harmful pathogens more effectively.
- Supports Oral Health: A well-balanced oral microbiome contributes to healthy gums and teeth, reducing the risk of cavities and gum disease.
- Releases Feel-Good Chemicals: Kissing triggers the release of dopamine, oxytocin, and serotonin, enhancing mood and reducing stress.
- Strengthens Relationships: Frequent kissing is linked to higher relationship satisfaction and deeper emotional bonds.
So, Should You Be Kissing More?
If kissing helps maintain a healthy and diverse microbiome, does that mean couples who kiss frequently are healthier?
The answer is complex.
While the exchange of bacteria can be beneficial, factors like diet, oral hygiene, and overall health play a bigger role in shaping a strong microbiome.
However, there’s no denying that kissing contributes to the mix.
The next time you lean in for a kiss, remember—you’re not just exchanging affection, you’re swapping millions of bacteria that may be shaping your health in ways science is still uncovering.
And if you’re on a first date, maybe keep this fun fact to yourself… at least until the second date.
Sources: EurekAlert, NPR, Microbiome Journal
