The immune system is rarely mentioned in public discussions about the health effects of vaping, yet it is one of the systems most directly exposed to e-cigarette aerosol with every puff. The respiratory mucosa — the immune-active surface lining the nose, throat and airways — is the first biological barrier that inhaled aerosol encounters, and the immune cells it hosts are among the first responders to any inhaled foreign material. Understanding how nicotine, propylene glycol, flavour compounds and fine aerosol particles interact with immune function helps explain why some vapers report more frequent infections, slower recovery, or changes in inflammatory conditions after switching. Users of all formats — from compact pod systems to rechargeable vapes — are exposing their immune system to an aerosol mix with specific immunomodulatory properties that are distinct from both cigarette smoke and clean air.
Nicotine as an Immunosuppressant: The Cholinergic Anti-Inflammatory Pathway
Nicotine has a well-characterised immunosuppressive effect mediated through the cholinergic anti-inflammatory pathway — a regulatory axis that normally limits excessive immune activation. Nicotinic acetylcholine receptors (nAChRs), particularly the alpha-7 subtype (α7-nAChR), are expressed on macrophages, dendritic cells, T-lymphocytes and natural killer (NK) cells — the frontline soldiers of both innate and adaptive immunity. When nicotine binds to α7-nAChR on macrophages, it suppresses the production of pro-inflammatory cytokines including tumour necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β) and interleukin-6 (IL-6).
This anti-inflammatory effect sounds potentially beneficial — and in the context of certain inflammatory diseases, activation of this pathway has genuine therapeutic interest. The problem is that the same cytokines that nicotine suppresses are essential for coordinating an effective response to bacterial and viral infection. Reduced TNF-α and IL-1β production impairs neutrophil recruitment to infection sites, reduces macrophage phagocytic activity (the killing of bacteria and virus-infected cells), and attenuates the fever response that creates an inhospitable environment for pathogens. The net effect of chronic nicotine-mediated α7-nAChR activation is a dampened inflammatory response that reduces both the discomfort of inflammation and the effectiveness of infection control.
Mucociliary Clearance: The Airways’ First Line of Defence
The respiratory mucosa’s primary mechanical defence against inhaled pathogens and particles is mucociliary clearance — the coordinated beating of cilia on airway epithelial cells that moves a layer of mucus (and everything trapped in it) upward and out of the airways. This system clears bacteria, viruses, dust, allergens and debris continuously and without any conscious effort. It is one of the most elegant defence mechanisms in human biology.
Both nicotine and propylene glycol have documented adverse effects on mucociliary function. Nicotine activates cholinergic receptors on airway epithelium that initially stimulate mucus secretion but with chronic exposure lead to ciliary dysfunction — the cilia beat more slowly and less coordinatedly, reducing clearance efficiency. Propylene glycol aerosol dehydrates the mucus layer through its hygroscopic properties, increasing mucus viscosity and making it harder for cilia to move. Several in vitro studies have shown that e-cigarette aerosol condensate reduces ciliary beat frequency in human airway epithelial cells within minutes of exposure, with effect sizes that are smaller than those produced by cigarette smoke but measurable at typical vaping concentrations.
Reduced mucociliary clearance is clinically significant because it allows pathogens that would normally be cleared from the airways to establish a foothold. This is one of the mechanisms through which both smokers and, to a lesser but real extent, vapers have higher rates of respiratory tract infections than non-users.
Alveolar Macrophages: Vaping’s Effect on Pulmonary Immune Surveillance
Alveolar macrophages are the immune sentinels of the deep lung — long-lived cells that patrol the alveolar surface, phagocytose (engulf and destroy) inhaled particles and pathogens, present antigens to adaptive immune cells, and regulate local inflammatory tone. They are among the cells most directly exposed to inhaled aerosol, and several research groups have characterised their functional changes in response to e-cigarette aerosol exposure.
A landmark 2019 study published in the Journal of Clinical Investigation found that e-cigarette aerosol exposure impaired alveolar macrophage function in both mice and human volunteers, reducing their phagocytic capacity, increasing lipid accumulation within the cells (a marker of dysfunction known as foam cell formation), and elevating inflammatory gene expression. The effect was present even with nicotine-free aerosol, implicating the non-nicotine aerosol components — likely propylene glycol, vegetable glycerin and flavour compounds — in macrophage dysfunction. The changes were distinct from those produced by cigarette smoke, suggesting that vaping creates its own specific pattern of alveolar immune disruption rather than simply a lesser version of smoking-related damage.
Critical finding: alveolar macrophage impairment from vaping is not primarily nicotine-driven — it appears to result from the aerosol base components themselves. This means nicotine-free vaping does not avoid this specific immunological risk, and it distinguishes vaping’s pulmonary immune effects from those of nicotine replacement therapy (patches, gum) which spare the airways entirely.
Adaptive Immunity: T-Cells, Antibodies and Vaccine Response
Beyond the innate immune cells of the airways, nicotine has documented effects on the adaptive immune system — the antigen-specific, memory-forming branch of immunity responsible for long-term protection against specific pathogens and for the effectiveness of vaccination.
T-lymphocytes express α7-nAChRs, and nicotine-mediated signalling through these receptors has been shown to skew T-helper cell differentiation away from Th1 responses (which are critical for defence against intracellular pathogens including viruses and Mycobacterium tuberculosis) and toward Th2 responses (associated with allergic inflammation and parasitic defence). This Th1/Th2 imbalance has implications both for infection susceptibility and for the effectiveness of vaccines that rely on Th1-polarised immunity.
Several studies have examined vaccination response in smokers compared to non-smokers and found reduced antibody titres following influenza and hepatitis B vaccination in smokers. Whether vaping produces equivalent attenuation of vaccine response is not yet established in large human trials, but the shared nicotine mechanism for T-cell modulation makes this a plausible concern that deserves monitoring — particularly given the public health significance of effective vaccination.
Vaping, COVID-19 and Respiratory Viral Infections
The COVID-19 pandemic generated a wave of research interest in the intersection of vaping and respiratory virus susceptibility. Early epidemiological analyses suggested that vapers may have had higher rates of symptomatic COVID-19 and more severe outcomes than comparable non-vapers, though these analyses were complicated by confounding factors including age, smoking history and socioeconomic status. The mechanistic basis for increased susceptibility is clear from the immune impairment research described above: reduced mucociliary clearance, impaired alveolar macrophage function, and nicotine-mediated suppression of the early innate antiviral response would each independently increase viral susceptibility and the probability of viral replication establishing in the deep lung.
E-cigarette aerosol has also been shown to upregulate ACE-2 receptor expression on airway epithelial cells — the receptor used by SARS-CoV-2 for cell entry. Whether this ACE-2 upregulation from vaping exposure was clinically significant in terms of COVID-19 susceptibility is debated, but the finding illustrates the multiple pathways through which vaping-related aerosol exposure can interact with infectious disease biology.
Practical Implications for Vapers
- If you notice more frequent respiratory infections — colds, sinusitis, bronchitis — since switching to vaping, this is consistent with the mucociliary and macrophage impairment evidence and worth discussing with a GP.
- Ensure vaccinations are up to date, particularly for influenza and pneumococcal disease. The potential for reduced vaccine response in vapers makes current vaccination particularly important.
- Avoid vaping during acute respiratory infections — continued aerosol exposure during an active infection when airway defence is already compromised by pathogen activity is a compounding insult to an already-stressed immune system.
- Use the simplest, least-flavoured e-liquid formulations where possible — the non-nicotine aerosol components appear to contribute meaningfully to alveolar macrophage impairment, and reducing the chemical complexity of the aerosol may reduce this specific immune risk.
- Progress toward nicotine reduction as part of a long-term plan — the nicotine-specific components of immune suppression (α7-nAChR activation, Th1/Th2 skewing) are dose-dependent, and lower ongoing nicotine exposure reduces the immunosuppressive burden proportionally.