It is common to observe that some individuals frequently experience colds or congested throats, while others in the same environment remain largely unaffected. This difference in susceptibility becomes
more pronounced with age, as natural immune decline (immunosenescence) combines with reduced saliva production, thinning gum tissues, and a loss of microbial diversity in both the gut and oral microbiome. As a result, many older adults notice they catch colds more easily than they did in their younger years, even when their lifestyle remains largely unchanged.
However, vulnerability to recurrent infections is not always just about exposure or basic immunity, there is more to the story. Research over the past two decades, with significant advances in the last ten years, has established a bidirectional gut–lung axis, highlighting how the gut and oral microbiome play a crucial role in shaping immune function and resilience against respiratory viruses.
Dr Debojyoti Dhar, co-founder and Director, Leucine Rich Bio (BugSpeaks), explains the science behind this connection.
The Role of the Gut and Oral Microbiota in Recurrent Colds
A large proportion of immune activity in the human body is influenced by microbial communities residing in the gut. These microorganisms perform critical regulatory functions behind the scenes, modulating immune responses, preventing excessive immune activation, and reducing unnecessary inflammation.
In particular, fibre-fermenting bacteria produce short-chain fatty acids (SCFAs) such as butyrate, propionate, and acetate. These compounds enter the bloodstream and exert anti-inflammatory effects at distant sites, including the lungs. SCFAs activate specific receptors (such as FFAR2 and FFAR3) on immune cells, promoting regulatory T-cell differentiation and helping to control excessive inflammation during viral infections.
“When this microbial balance is disrupted, the immune system may become either under-responsive or excessively reactive,” explains Dr Dhar. “Both extremes can increase susceptibility to recurrent infections.”
The oral microbiome plays an equally important role, especially in infections affecting the nose, throat, and lungs. The mouth and upper airway act as primary entry points for many pathogens. A disrupted oral microbial balance can weaken natural defence mechanisms, allowing viruses and opportunistic bacteria to establish infection more easily.
Beneficial oral microbes such as certain Streptococcus species compete with pathogens and produce antimicrobial compounds. In contrast, oral dysbiosis marked by pro-inflammatory strains increases the risk of harmful bacteria being aspirated into the lower airways, creating conditions that favour infection.
Everyday Factors That Influence Microbial Balance
Several lifestyle factors influence the health of both gut and oral microbiota. Poor dietary diversity, low fibre intake, chronic stress, inadequate sleep, and repeated antibiotic use are known to disrupt microbial balance. Over time, these disruptions impair how efficiently the immune system responds to routine viral exposures.
Understanding why some people catch colds more often requires moving beyond the idea of immunity as a simple on–off switch. Instead, immunity should be viewed as a dynamic system shaped by microbial health. Supporting the gut and oral microbiome through informed lifestyle choices is emerging as a key strategy for maintaining long-term immune resilience.
