Oral microbiome dynamics during travel : environmental exposure, dysbiosis, and resilience

 1. How much do people travel each year ?

According to the European Commission, EU residents aged 15 years and older made nearly 1.2 billion tourism trips with overnight stays in 2024, corresponding to approximately three trips per person per year.¹ This frequency of travel is biologically significant, as repeated movement between environments creates repeated opportunities for microbial exposure and short-term ecological disruption. While travel-associated changes in the gut microbiome and the clinical syndrome of travelers’ diarrhea are well documented, the oral microbiome—including saliva-, tongue-, and plaque-associated communities—has received far less attention, despite serving as a primary interface between the host and the external environment. 

2. Why travel should reshape the oral microbiome

The oral cavity is continuously exposed to the external environment, making it particularly sensitive to rapid lifestyle and environmental changes. Although oral microbial communities are generally stable within individuals, they respond to shifts in diet, oral hygiene practices, circadian rhythms, stress, and immune status. Oral health depends on community balance (homeostasis), and dysbiosis—disruption of community structure or function—is associated with both oral and systemic disease.²
Travel concentrates multiple perturbations simultaneously, including exposure to new environments, water sources, dietary patterns, and social contacts,^3-4 all of which can influence resident microbial communities. As the entry point to the gastrointestinal tract, the oral cavity may also influence downstream microbial ecology. Large, multi-country studies have shown that oral microbes can transmit to and colonize the gut more frequently than previously appreciated, even in healthy individuals.⁵

3. When travel introduces new microbes: dysbiosis, food poisoning, and diarrhea

A well-recognized risk of travel is acute gastrointestinal infection, often caused by food- or water-borne pathogens, which can coincide with microbial community disruption. Longitudinal studies show that microbiome composition shifts during travel and that diarrheal episodes can destabilize community structure and increase antimicrobial resistance gene abundance for weeks.^6-7 Travel is also associated with colonization by multidrug-resistant organisms, particularly among individuals who experience travelers’ diarrhea.⁶ Clinically, most uncomplicated cases of travelers’ diarrhea resolve within days. However, microbiome studies suggest only partial resilience: microbial composition often trends back toward baseline after return, but recovery may be delayed or incomplete. Notably, travel-associated antimicrobial resistance signatures can persist for weeks following the initial disruption in some cohorts.^{6, 8-9}

4. The underexplored questions: acclimation time, stability, and permanence

Despite growing interest in travel-related microbiome dynamics, direct longitudinal sampling of the oral microbiome during travel remains rare. Time-series studies of the gut microbiome in non-travel settings reveal substantial day-to-day variability even under stable conditions, highlighting the need for dense longitudinal sampling to distinguish normal temporal variation from true travel-induced effects.⁴

Leveraging a year-long international gap-year program, Dr. Wendy Lin is tracking oral microbiome changes in a student cohort as they travel across seven regions, including the United States, Brazil, France, Turkey, Kenya, India, and China. This study aims to address fundamental questions that remain poorly characterized for the oral microbiome:

• How long does it take for the oral microbiome to acclimate to a new environment?

• Is the travel-associated oral microbiome stable or highly dynamic?

• How quickly does the oral microbiome revert to baseline after returning home?

• Do newly introduced taxa or strain-level variants persist long-term?

Conclusion

Travel predictably alters environmental exposures and dietary patterns, creating a natural experiment for studying human microbiome ecology. Evidence from gut microbiome studies of travelers demonstrates rapid compositional shifts during travel and additional disruption during diarrheal illness, often followed by delayed or incomplete recovery. The oral microbiome—despite being the first point of contact for food, water, and environmental microbes—remains comparatively undercharacterized in this context. Longitudinal studies of traveling cohorts with dense oral sampling have the potential to answer foundational questions about microbial acclimation, stability, and long-term persistence, and to determine whether travel leaves lasting microbial imprints after individuals return home.