The concern is known as third-hand exposure. It differs from second-hand exposure, which occurs when a person inhales airborne smoke or aerosol produced by someone else. Third-hand exposure begins after the air appears clear. Chemicals deposited during vaping can persist indoors, change through reactions with oxygen and other compounds, and later return to the air or transfer to hands, toys and food. A child crawling on a contaminated floor, touching a chair or mouthing a toy may encounter substances that adults cannot see and may not detect by smell.

Electronic cigarettes do not produce the same mixture as conventional tobacco cigarettes, but “different” does not mean chemically harmless. Their aerosols can contain nicotine, ultrafine particles, volatile organic compounds, carbonyl compounds such as formaldehyde and acetaldehyde, and trace metals released from heating coils and other device components. The exact composition varies widely according to the device, liquid formulation, battery power, temperature and user behaviour. When these substances settle on indoor surfaces, they may react with ozone, light or surface materials, creating new compounds whose biological effects are not necessarily identical to those of the original aerosol.

The developing lung may be especially vulnerable to such exposure because childhood is a period of rapid structural and functional change. The airways grow, the gas-exchange surface expands and immune defenses mature over time. Exposure to irritants during these stages could influence epithelial barrier function, inflammatory signalling and the behaviour of cells responsible for repairing airway tissue. The lung’s epithelial lining is not merely a passive wall: it regulates interactions with inhaled particles, coordinates immune responses and helps maintain the delicate environment required for efficient oxygen exchange.

A further complication is that children interact with their surroundings differently from adults. Infants spend more time close to floors and other contaminated surfaces, breathe more air relative to their body mass and frequently place their hands or objects in their mouths. These behaviours create several possible exposure pathways at once: inhalation of resuspended particles, skin contact and ingestion of residues transferred from surfaces. Clothing and hair may also act as temporary reservoirs, carrying chemicals from a vaping environment into cars, bedrooms, childcare settings or other spaces where vaping did not occur.

The term “third-hand smoke” was originally developed to describe persistent tobacco residues, but the same framework may apply to electronic-cigarette emissions. The residues are not necessarily static. Some compounds can off-gas gradually, while others can be moved through ordinary activity such as walking, cleaning, handling fabrics or opening windows. Surface chemistry can also transform deposited nicotine and other substances into secondary products, including nicotine-derived compounds that may have their own toxicological importance. This means that a room can remain chemically influenced by vaping even when no aerosol is visible and no one is actively using a device.

Larcombe’s article highlights a major gap between how exposure is perceived and how it may occur biologically. Household rules that prohibit vaping in a child’s immediate presence can reduce direct second-hand exposure, but they may not eliminate contamination if vaping takes place indoors or in enclosed spaces such as vehicles. Ventilation can dilute airborne chemicals, yet it cannot necessarily remove material that has already settled onto surfaces. Similarly, air purifiers may reduce some airborne particles while leaving residues on upholstery, clothing or walls. The most reliable way to prevent third-hand exposure is therefore to keep vaping and its emissions entirely outside environments occupied by children.

The issue is also relevant to clinical medicine and risk communication. Parents may reasonably assume that the absence of smoke, smell or visible vapour indicates a clean environment. That assumption is more complicated with electronic cigarettes because their emissions often dissipate quickly while leaving behind substances that are difficult to monitor without laboratory testing. Researchers still need better measurements of how long individual compounds persist, how much transfers to children, and which chemical mixtures are most strongly associated with respiratory effects. Long-term studies will be necessary to determine whether repeated low-level exposure contributes to asthma symptoms, altered lung development, increased susceptibility to infection or other outcomes.

The emerging message is not that every trace of e-cigarette residue will cause disease, nor that vaping-related exposure is identical to tobacco smoke. Rather, it is that the absence of visible aerosol should not be mistaken for the absence of exposure. As vaping becomes more common, especially in homes and vehicles where children spend time, scientists and health professionals are being urged to expand the definition of a smoke-free environment. For the developing lung, a genuinely protective standard may require more than asking adults not to vape nearby. It may require keeping vaping residues out of children’s surroundings altogether.

Subject of Research: Third-hand e-cigarette residues and their potential effects on the developing lung

Article Title: When ‘vape-free’ should mean ‘smoke-free’: third-hand e-cigarette residues and the developing lung

Article References: Larcombe, A.N. “When ‘vape-free’ should mean ‘smoke-free’: third-hand e-cigarette residues and the developing lung.” Pediatr Res (2026). https://doi.org/10.1038/s41390-026-05380-y

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41390-026-05380-y

Keywords: third-hand exposure, e-cigarette residues, vaping, developing lung, children’s health, indoor air quality, nicotine, respiratory health

Thirdhand exposure refers to chemical material left behind after an aerosol or smoke has been released into the environment. Unlike firsthand exposure, which occurs when someone directly inhales a product, or secondhand exposure, which involves breathing airborne emissions, thirdhand exposure can occur when residues settle on clothing, furniture, bedding, walls or other surfaces. These compounds may later be released back into the air, transferred through skin contact or ingested when contaminated particles reach the mouth.

Electronic-cigarette aerosols are complex chemical mixtures rather than harmless water vapor. Depending on the device, liquid formulation and heating conditions, they can contain nicotine, flavoring chemicals, carbonyl compounds, metals and ultrafine particles. Once deposited indoors, these substances may react with oxygen, ozone, moisture and other chemicals, producing a changing mixture that can remain in the environment. Infants may be particularly vulnerable because they spend substantial time close to floors and fabrics, have developing immune and respiratory systems, and breathe more air relative to their body size than adults.

The study by A. Zaman, T. Cook, D. B. Mabou and colleagues examined how neonatal mice responded to these aged electronic-cigarette aerosol residues. Its focus was not simply whether exposure caused an immediate respiratory reaction, but how early-life contact influenced the developing lung and the biological programs that control its function. The researchers assessed lung performance alongside the transcriptome—the complete collection of RNA molecules produced by cells at a particular time.

Transcriptomic analysis provides a high-resolution view of how exposure affects cells. When a gene is activated, its DNA sequence is copied into messenger RNA, which helps direct the production of proteins. By measuring changes in thousands of RNA transcripts, scientists can identify pathways involved in inflammation, oxidative stress, tissue repair, immune signaling, metabolism and lung development. These molecular changes can reveal biological disruption even when visible tissue damage is limited or traditional measurements show only subtle effects.

The researchers’ findings indicate that thirdhand electronic-cigarette aerosol exposure modified lung function in neonatal mice and produced sex-specific changes in gene expression. In other words, male and female animals did not show identical responses to the same environmental challenge. Such differences can arise from the influence of sex hormones, chromosomes, developmental timing, immune regulation or differences in how chemicals are absorbed and metabolized. During the neonatal period, when airways and the gas-exchange surfaces of the lung are still maturing, even modest molecular disturbances could potentially influence later respiratory health.

The sex-specific signal is particularly important because biomedical research has often treated male and female biology as interchangeable. Yet respiratory diseases, immune disorders and responses to environmental pollutants can differ between sexes. A chemical exposure may activate inflammatory genes more strongly in one sex, alter antioxidant defenses differently in another or affect the development of airway structures through distinct signaling pathways. The new results add electronic-cigarette residues to a growing list of environmental factors that may interact with biological sex during early development.

The study does not establish that thirdhand vaping residues cause the same effects in human babies, nor does it determine how long any changes persist after exposure ends. Mouse lungs develop on a different timetable from human lungs, and controlled laboratory exposure cannot reproduce every feature of a household environment. The concentration, age and chemical composition of the residues also matter, as do ventilation, surface type, cleaning practices and the presence of nicotine or flavoring compounds. Nevertheless, animal studies are essential for identifying mechanisms that would be difficult or unethical to test directly in infants.

The findings also challenge the idea that vaping-related exposure ends when a device is switched off. While electronic cigarettes generally produce fewer combustion products than conventional cigarettes, reduced emissions do not mean zero risk, especially in enclosed spaces containing newborns. Residues may accumulate through repeated use and persist on surfaces that infants touch or mouth. The researchers’ work suggests that public-health guidance should consider not only direct and secondhand aerosol exposure, but also the less visible chemical legacy left in indoor environments.

For families, the practical message is straightforward: keeping electronic cigarettes, refill liquids and aerosol-generating devices away from infants is important, but preventing use around children may not eliminate every route of exposure if residues have already accumulated. Cleaning contaminated surfaces, washing hands and changing outer clothing after vaping may reduce contact, although the effectiveness of these measures depends on the chemicals involved. The strongest protection remains maintaining smoke- and aerosol-free homes and vehicles.

The study’s most significant contribution may be its combination of lung-function testing with transcriptomic analysis. By linking physiological measurements to altered gene activity, it provides a fuller picture of how early-life exposure could influence developing respiratory systems. Further research will need to identify which chemicals drive the observed effects, whether the changes are reversible, how they evolve with age and whether similar sex-specific patterns occur in human children. Until those questions are answered, the invisible residues of vaping deserve far more scientific and public attention than they have received.

Subject of Research: Thirdhand electronic-cigarette aerosol exposure and its sex-specific effects on lung function and gene expression in neonatal mice.

Article Title: Sex-specific modulation of lung function and transcriptome in neonate mice exposed to thirdhand electronic-cigarette aerosols.

Article References: Zaman, A., Cook, T., Mabou, D.B. et al. “Sex-specific modulation of lung function and transcriptome in neonate mice exposed to thirdhand electronic-cigarette aerosols.” Pediatric Research (2026). https://doi.org/10.1038/s41390-026-05282-z

Image Credits: AI Generated

DOI: 10.1038/s41390-026-05282-z

Keywords: electronic cigarettes, thirdhand aerosol, neonatal mice, lung function, transcriptome, gene expression, sex-specific biology, infant health, vaping exposure, respiratory development