Sharing (Bacteria) Is Caring: How Your Relationships Influence Your Microbiome

Written by Emma Loewe: Writer, author, and editor of Cultured. Her writing explores the intersection of nature, climate, and human health. Emma is the author of “Return to Nature” and “The Spirit Almanac.”
Reviewed by Jennie O’Grady: Senior SciComms Specialist at Seed Health. Dr. O’Grady is a trained clinician with a background in clinical research and expertise in physiology and the microbiome. With certifications in nutrition science and microbial science, she is passionate about educating audiences on the latest research on health, wellness, and advancements in the microbiome.

The Seed Digest

• Humans constantly exchange microbes with each other. Transfers occur every time we shake hands, hug, or just sit in the same train.
• The bacteria, viruses, and fungi we share can go on to shape our microbiomes in both positive and negative ways.
• Our microbiomes tend to be most similar to the people we spend the most time with—from family members and romantic partners to roommates and coworkers.

When you come into contact with another person, you swap more than just pleasantries and gossip. You share microbes—bacteria, viruses, and fungi that are invisible to the naked eye.¹

Picture that your body is home to the world’s largest lending library, with trillions of books being checked in and out at all times. Roommates, friends, neighbors, and fellow commuters constantly leave you with new and potentially transformative titles to sift through. Your health, like any great archive, is a community effort. The microscopic lifeforms you pick up from others can help shape the various microbiomes of your body—from your gut to your lungs—and form a blueprint of how you navigate the world. 

Let’s explore how your microbiome tells the story of your relationships—from the fleeting to the forever.

The Benefits and Risks of Microbial Transfer

People who physically spend more time together tend to have more similar microbiome compositions, demonstrating that close interactions facilitate the transfer of microorganisms.^2,3

Microbial swaps happen every time we shake hands, hug, kiss, sneeze, or talk closely to another person—either through direct skin-to-skin contact or airborne transfer.⁴ When we touch surfaces in public spaces (door handles, grocery carts, etc.), we can also indirectly pick up microbes that others leave behind.⁵ Most of these microbes do not colonize or persist in our systems long-term, though some can.

Most of us are already aware of the potential negative consequences of these exchanges: Bacteria, viruses, and fungi that cause disease (germs) can spread from one person to another through direct and indirect contact. Horizontal gene transfer (any spread of genes that don’t pass through a parent to their offspring) is also a primary driver of antibiotic resistance.⁶

However, the vast majority of the microbes we get from other people are harmless, and some are beneficial, as demonstrated in these examples:

• Microbial transfer can enhance bacterial diversity in the gut: Some microbiomes of the body—most notably, the gut—function best when they contain many different species of bacteria. This makes sense when you consider the library analogy again: The more types of books you have on your shelves, the more likely you are to find one you want to read at any given moment. Bacterial diversity in the gut imparts you with a wider array of traits you can leverage to maintain a strong, resilient internal environment, and it’s often linked to improved digestion, immune system function, and metabolic capabilities.⁷ “Maintaining healthy social connections may play a crucial role in supporting a balanced and diverse gut microbiome,” explains Jennie O’Grady, a Senior SciComms Specialist at Seed. This is yet another reason that loneliness and social isolation can be so insidious to health: When we keep to ourselves, we miss out on the microbial offerings of others. 
• Microbial transfer can help protect us from disease: In some cases, the addition of commensal bacteria in a diverse microbiome can outcompete pathogens for space and nutrients, preventing them from establishing themselves in the body and spreading disease.⁸ Exposure to diverse microbes also plays a crucial role in training and regulating the immune system.⁹ Different bacteria have distinct molecular patterns that are recognized by immune cells through pattern recognition receptors.¹⁰ The more these cells are trained to differentiate harmless from harmful foreign microbes, the better they’ll become at attacking the bad guys and letting the good guys through.

The Ties That Microbially Bind You

Here are just a few examples of relationships that have scientifically validated impacts on the microbiome. 

Roommates

Research shows that the more time you spend with someone, the more bacteria you share. It’s no surprise that people living under the same roof often have very similar microbial profiles, with an average of 12 to 32% of bacterial strains in the gut and mouth in common.¹¹

Even cohabitants who don’t cross paths much still exhibit similarities, likely due to the indirect exchange of microbes in their environment. We shed millions of microbial cells from our skin, gut, and respiratory tracts per hour, leaving an invisible mark on doorknobs, blankets, utensils, and anything else we touch.^4,12 

Even the most diligent of cleaning routines can’t wipe these microbial fingerprints away entirely, so it’s no wonder that you and your roommate seem to always get sick at the same time. 

Neighbors

“People who live in the same village tend to have more similar strains of gut bacteria compared to people from different villages, even if they are not from the same household,” Dr. O’Grady explains.¹¹ This is likely because neighbors tend to not only come in contact with each other but also share certain resources like water and food. They are also exposed to the same environments, and they can have microbial exchanges in shared spaces like parks and grocery stores. 

In one detailed microbiome sequencing of 1,787 adults within 18 isolated villages in Honduras, researchers concluded that these communities exhibited “social niches,” with neighbors who spent the most time together possessing the most similar bacterial species and strains. The most social members of the villages also tended to have microbiomes that were representative of their communities as a whole.¹³

Friends (and Friends-of-Friends)

Every time you grab dinner or go on a walk with a friend, you exchange microbes. Research shows that acquaintances who greet each other with a handshake or hug tend to have increased microbial exchange and kisses on the cheek have the highest strain-sharing rate. Your gut microbiome might not only reflect your friends but also their friends, with second-degree social connections influencing strain sharing as well.¹³

Romantic Partners 

Romance unlocks entirely new ways to exchange microbes 😉. Just consider that approximately 80 million bacteria are transferred per 10-second smooch, according to research on hetero- and homosexual couples. This minging of microbes from the tongue, hard palate, soft palate, cheeks, and lips may serve an evolutionary purpose: Chemical cues from a person’s mouth (including those produced by bacteria) may subconsciously clue you into their mating potential.¹⁴ Sex is another bacterial smorgasbord for the oral, vaginal, penile, and even gut microbiomes.

Couples who live together tend to have more shared microbial profiles. Although, married couples who report being “somewhat close” to each other have less similar gut microbiomes than those who feel they are “very close,” indicating that the quality of the bond matters too.^3,15

Parents

No relationship is as microbially meaningful as the one between a mother and child—particularly during the first year of life. Mothers pass on microbes to their offspring during childbirth (either via the vaginal canal or the skin in cesarean births) and then through skin-to-skin contact and breastfeeding, establishing the infant’s microbiome.^11,16

While our microbial landscapes change and evolve as we get older, we never completely “outgrow” this initial exposure. Some research shows that the average 30-year-old retains 14% of their mother’s original bacterial strains, and the most highly persistent strains are still present by the time we hit our eighties.¹¹ 

Fathers/parents who did not give birth can also share microbial similarities with their children—though they are likely the result of spending time together and/or living under the same roof. Families with dogs may share even more skin microbiota (with the furry friend acting as a microbial transporter of sorts) and pet ownership in general is associated with greater skin microbiome diversity.^15,17

Siblings 

Biological siblings usually have more similar gut microbiomes than unrelated individuals—likely due to the presence of strains passed down by a shared mother and shared early-life environments. Living with an older sibling—especially during early childhood—can also significantly influence the diversity and relative abundance of bacteria in the respiratory and gut microbiomes.¹⁸ Cohabitating twins and siblings who are close in age seem to have even more strains in common (though this number tends to go down the longer they live apart).^11,19

Coworkers and Co-commuters

Like roommates, coworkers who share an office can frequently transmit microbes to each other via high-touch surfaces.^5,20 Keyboards and bathroom faucet handles seem to have particularly high bacterial counts in the work microbiome.²¹ 

Your commute is another source of microbial exposure, especially if you take public transit. Based on samples of the Mexico City Metro (Sistema de Transporte Colectivo), we know that surfaces like handrails, seats, horizontal and vertical poles, hanging grips, and walls within train cars all harbor microbial communities, and commuters’ skin microbiomes tend to have more microbial diversity and species richness following a ride. Even if these surfaces are frequently cleaned, research shows that certain microbial communities can reestablish within minutes.²² 

The subway microbiome seems to shift in response to the weather, seasons, and even the time of day, offering a glimpse into transportation systems’ history.^23,24 For example, researchers found marine-associated bacteria in a NYC subway station that had flooded during Hurricane Sandy years earlier.²⁵

Microbiome Care Is Community Care

Research demonstrates the (many) ways we share microbes every day—from when we wake up and turn on the coffee machine to when we take a train home from work and spend the evening catching up with family. This means that taking care of your own microbiome is also a way to take care of those around you.

Here are just a few ways to foster balance for the sake of your microbiome, your health, and your loved ones:

• Promote gut diversity by eating a wide range of nutrient-rich foods, and prioritizing fiber, prebiotics, monounsaturated fats, and fermented ingredients.
• Spend time outside every day, seeking out microbially diverse greenspaces whenever you can. 
• Foster meaningful social relationships and prioritize in-person meetups.
• Take (or gift!) DS-01^® Daily Synbiotic for gut and whole-body benefits. The two-in-one probiotic and prebiotic formula delivers 24 clinically and scientifically studied probiotic strains to promote gut health that’s worth sharing.*
• Opt for gentler products over antibacterial cleaners and bleaches so you don’t wipe out the “good” bacteria from your home environment.

EXPLORE FURTHER: Routines Over Resolutions: 12 Healthy Habits for Your Microbiome

Frequently Asked Questions (FAQs)

How is our microbiome shaped by family, friends, and neighbors?

People who spend more time together tend to have more similar microbiomes due to frequent microbial exchanges through physical contact, airborne transmission, and shared surfaces and environments. While this facilitates the spread of pathogens in some cases, it can promote beneficial diversity in others. 

What can people do to maintain a diverse and balanced microbiome?

To promote diversity in the gut microbiome, consume fiber-rich foods, minimize disruptors like alcohol and stress, drink plenty of water, and get regular physical activity. (But a quick PSA: Not all microbiomes of the body benefit from diversity. The vaginal microbiome, for example, functions best when dominated by a single bacterial genus, lactobacillus.)

The Key Insight

Your microbiome isn’t just yours—it’s a living archive of handshakes and hugs, shared meals and subway rides. While not every microbial exchange is a welcome one (looking at you, flu season), the vast majority are harmless—or even beneficial. So, the next time you gather with friends or loved ones, take comfort in knowing that you’re not just making memories. You’re making microbiomes.