What Remains After the Aerosol Is Gone?

On a windowsill sits an amount of nicotine too small to see. There is no stain, no lingering odor, nothing that would reveal its presence without the aid of an analytical instrument. Yet that invisible trace has become the subject of differing scientific interpretations.

For some researchers, it marks the beginning of a new kind of exposure. An aerosol has been released, nicotine has settled onto a surface, and it may eventually find its way back to another person. In this view, the residue deserves a name: third-hand vaping, because it extends exposure beyond the moment when the visible cloud has disappeared.

For Roberto A. Sussman, a physicist at the Institute of Nuclear Sciences at the National Autonomous University of Mexico (UNAM), the same molecule tells a more limited story. It shows that deposition has occurred. By itself, it does not show that a persistent reservoir has formed; one capable of changing over time, recirculating through the indoor environment, and reaching people in biologically meaningful doses.

That question is the focus of Sussman’s single-author critical review, “On the Detection and Scope of “Third-Hand Vaping’", published in July 2026 in the International Journal of Environmental Research and Public Health.

To understand what is at stake, however, it helps to begin with the phenomenon that inspired the analogy in the first place.

The visible plume from a burning cigarette disappears quickly. The pollutants it carries do not. They accumulate on walls, fabrics, dust, and other household surfaces, where they continue to undergo chemical changes for weeks, months, and in some cases even years.

The smoke fades; the residue remains. That lingering form of exposure came to be known as third-hand smoke. It occurs after the cigarette is extinguished, through contact with the contaminants left behind indoors or with new compounds formed from those residues over time.

As electronic cigarettes became more widespread, researchers began asking whether vaping aerosols might leave behind an equivalent kind of contamination.

The term third-hand vaping emerged from that analogy: first comes direct exposure, then secondhand exposure, and finally exposure to the residue left on indoor surfaces.

Studies had already shown that nicotine from e-cigarette aerosol can settle onto surfaces. But deposition alone does not establish an equivalent to third-hand smoke. To make that case, researchers would need to demonstrate not only that residues are present, but that they persist, undergo meaningful chemical transformations, reach people through plausible exposure pathways, and do so at levels capable of causing harm.

The similarity in terminology, by itself, is not evidence that the two processes behave the same way, or pose comparable risks.

The Problem That Begins After the Cigarette Ends

Any comparison has to begin with the lit cigarette. With each puff, it produces the smoke that the smoker inhales. Between puffs, it keeps burning, releasing sidestream smoke directly from the smoldering tip. That emission accounts for a substantial share of the material released into the surrounding air.

As long as it remains lit, a cigarette acts as a continuous source of combustion. Its smoke contains particles, volatile and semivolatile organic compounds, hydrocarbons, and many other substances. Some remain suspended in the air; others settle onto walls, furniture, fabrics, and dust.

Deposition is not the end of the process. Once on a surface, residues may continue to react, undergo chemical transformations, and return to the air. Exposure can occur through skin contact, the ingestion of dust, hand-to-mouth transfer, or the reemission of compounds into the indoor environment.

Taken together, the amount released, the degree of deposition, the persistence of the residue, its chemical transformations, and the pathways by which people encounter it define third-hand smoke. Any comparison with e-cigarettes has to account for all of them, not merely the detection of nicotine on a surface.

Young children are especially vulnerable. They spend more time close to the floor, crawl, touch furniture and objects, and frequently put their hands in their mouths. Because they weigh less, the same absorbed amount can translate into a larger dose relative to body size. Exposure may also be greater in small or poorly ventilated homes, where the same emission is dispersed through a smaller volume of air and residues can accumulate on surfaces within easy reach.

It was from this model that researchers began to examine e-cigarettes. The logic seemed straightforward: exhaled aerosol contains nicotine; some of it can settle; vaping might therefore leave behind an environmental reservoir resembling the one produced by conventional cigarettes.

Laboratory studies detected nicotine on glass, metal, flooring, and fabrics exposed to e-cigarette aerosol. Field studies in vape shops also found nicotine and some of its derivatives on indoor surfaces. The term third-hand vaping began to circulate before it was clear whether the resemblance extended beyond deposition to include persistence, chemical transformation, and meaningful exposure.

Sussman sees an inferential leap here.

Finding nicotine on a surface shows that matter has been transferred. It does not, by itself, show that a persistent source of exposure has formed under ordinary conditions.

To establish that link, researchers would need to know how much material was released, how much remained airborne, how much settled, how long it persisted, what chemical changes it underwent, and how often these processes occur in homes, bedrooms, cars, and offices.

Deposited nicotine establishes presence. Risk depends on what happens next.

The first major difference lies in where the material comes from. Cigarette smoke is produced by burning tobacco, a process that generates a complex mixture of gases and particles. E-cigarette aerosol is created by heating a liquid usually made from propylene glycol, glycerin, water, nicotine, and flavorings. Although it is commonly called vapor, it contains liquid droplets as well as gaseous compounds, and its composition begins to change as soon as it mixes with the air.

A cigarette continues to emit smoke for as long as it remains lit. An e-cigarette produces aerosol only when the device is activated, and that aerosol reaches the surrounding environment chiefly through the user’s exhalation. There is no burning tip releasing material between puffs.

That difference affects the total amount emitted. Some of the nicotine and other inhaled components remain in the body, so only a fraction returns to the environment. With a conventional cigarette, exhaled smoke is added to the smoke continuously released by the burning tip. With vaping, environmental contamination depends largely on what the user exhales.

Measurements in homes confirm that some of this nicotine remains airborne. Ballbè and colleagues found higher average concentrations of airborne nicotine in the homes of e-cigarette users than in control homes. The finding shows that vaping can produce measurable environmental exposure. By itself, however, it does not reveal how much of that material settles, how long it remains on surfaces, or whether it later reaches another person.

After exhalation, the droplets enter a larger and cooler volume of air. Some components evaporate, the cloud disperses, and the droplets change in size. The fact that the aerosol is no longer visible does not mean that all of its material has vanished, but it does indicate a rapid drop in concentration.

Tobacco smoke tends to contain a larger share of low-volatility particles and compounds that linger indoors. That creates more opportunities for deposition, absorption into porous materials, and reaction with other substances in the indoor environment.

In Sussman’s reading, the lower environmental emissions and rapid dilution of e-cigarette aerosol tend to limit the amount of material available to form long-lived reservoirs. The emissions occur over shorter periods, and less material is likely to enter the environment than would be released by a continuously burning source.

The residues are real. What remains to be shown is whether, under ordinary conditions of use, they reach levels of abundance, persistence, and chemical activity comparable to those left by combustion.

High surface deposits can be produced in experiments conducted in small, poorly ventilated spaces, with many puffs and long exposure periods. In such cases, the results reflect the properties of the aerosol and also the conditions engineered to concentrate and retain it.

The Chemical Divide Between Smoking and Vaping

The difference between smoking and vaping is not simply a matter of how material enters the environment. It also lies in the composition of the residues that are left behind and in the chemistry that unfolds after they settle.

Physics explains how particles disperse through the air and reach indoor surfaces. Chemistry explains what happens once they get there.

A simpler mixture is not necessarily a harmless one. It can still contain compounds that can cause harm. But the diversity, abundance, and pathways by which chemicals are formed in e-cigarette aerosol differ fundamentally from those of smoke produced by combustion. For that reason, the chemical behavior of cigarette smoke cannot simply be mapped onto vaping by analogy alone.

Once deposited, nicotine can react with other substances in the environment. What follows depends on how much has accumulated, what other compounds accompany it, the nature of the surface, and how long it remains there. In cigarette smoke, nicotine is part of a chemically complex mixture that is continuously replenished by combustion and capable of persisting indoors. According to Sussman’s review, e-cigarette aerosol generally does not create those same conditions on the same scale.

Nicotine from vaping can settle onto surfaces and undergo subsequent chemical changes. Its presence alone, however, does not demonstrate that vaping and smoking follow the same chemical trajectory.

The studies that detected nicotine on glass, fabrics, metals, and flooring help define that distinction. Many were conducted in sealed environmental chambers, where vaping machines, pumps, or syringes generated standardized puffs. Samples of different materials were exposed to aerosol for predetermined periods, allowing researchers to measure deposition, retention, and any resulting chemical reactions.

This experimental design isolates processes that are difficult to observe in everyday settings. Air volume, temperature, puff number, and exposure time can all be tightly controlled. At the same time, the enclosed environment limits dispersion and encourages accumulation.

In one study included in Sussman’s review, one hundred puffs were generated over the course of ninety minutes. In another, forty-nine puffs were injected into a one-cubic-meter chamber in just fifteen minutes. A third subjected aerosol residues to an extended sequence of procedures before examining the formation of new particles.

One experiment, in particular, highlights an important distinction.

Marcham and colleagues exposed glass and cotton to e-cigarette aerosol and tracked the residues over time. The visible cloud disappeared within minutes, but nicotine remained detectable for days. Their models estimated that concentrations returned to background levels after roughly four days on glass and sixteen days on cotton.

The rapid disappearance of the aerosol from the air and the persistence of nicotine after deposition are therefore two different phenomena.

The findings show that surfaces—particularly absorbent materials—can retain nicotine long after the visible cloud has vanished. However, because the experiment took place in a controlled chamber, it does not establish how long comparable concentrations would persist in a ventilated home.

Taken together, these studies show that under certain conditions components of e-cigarette aerosol can settle onto surfaces, remain in materials, and participate in subsequent chemical reactions. They do not, by themselves, establish how often, or to what extent, those processes occur in homes, bedrooms, cars, or offices.

A one-cubic-meter chamber concentrates aerosol very differently from a lived-in home. In everyday environments, air circulates, doors and windows open, people move about, and deposited material is unevenly distributed across surfaces. Temperature, ventilation, and room volume also vary.

That difference does not invalidate the experiments. It defines the limits of what they can tell us. A study may show that a chemical reaction is possible without showing that it occurs to a meaningful extent under ordinary conditions of use. It may demonstrate that a material retains nicotine without establishing that someone would receive a biologically significant dose from touching it.

This distinction is central to Sussman’s critique. Environmental chambers make certain mechanisms measurable, but they do not necessarily reproduce how frequently or how intensely those mechanisms operate in everyday settings.

In environmental health, detecting a substance is only the beginning of the analysis. Risk also depends on concentration, the duration and frequency of exposure, the route by which a substance enters the body, ventilation, human behavior, and the vulnerability of the people exposed. The question is not simply whether e-cigarette aerosol leaves nicotine behind, but how much, for how long, and with what consequences.

The Special Case of Vape Shops

Vape shops offer a different kind of evidence. They are not laboratory chambers. They have employees, customers, furniture, air circulation, and the rhythms of everyday business. Nor are they representative of an ordinary home.

In many of these stores, customers sampled devices on site. For any one individual, the emissions were intermittent. Over the course of a day, however, dozens of vaping sessions could overlap within a confined space. A busy vape shop might accumulate more aerosol in a few hours than the home of a single e-cigarette user would over the same period.

In one of the studies reviewed by Sussman, three participants generated roughly 1,000 puffs over two hours in a 57-cubic-meter room. In other experiments, test materials remained exposed for weeks or even months. Under those conditions, repeated emissions and prolonged exposure favored both nicotine deposition and accumulation.

The sampling methods matter, too. Some researchers placed towels, cotton fabric, paper, or children’s clothing throughout vape shops before measuring how much nicotine those materials retained. These items served as passive samplers, selected because of their ability to absorb airborne compounds.

The findings show that nicotine circulated through the indoor air and reached those surfaces. They do not show that clothing, toys, furniture, or carpeting in a typical home would accumulate comparable concentrations under ordinary patterns of use.

One study by Khachatoorian and colleagues extended the investigation beyond the vape shop itself. In a commercial building occupied by multiple businesses, researchers detected nicotine, other tobacco alkaloids, and tobacco-specific nitrosamines not only inside the vape shop but also in a neighboring business where no vaping occurred. Control samples collected in the hallway did not show the same pattern.

The findings suggest that compounds associated with e-cigarette aerosol can migrate beyond the space where vaping occurs and settle in adjacent environments. They do not, however, answer the question of what happens in homes. The source remained a retail shop with frequent, concentrated vaping, a setting fundamentally different from a residence occupied by a single user.

Comparisons with smokers’ homes introduce another layer of complexity. The number of users, the frequency of emissions, room size, ventilation, occupancy patterns, and the nature of the emission source may all vary simultaneously.

A vape shop where dozens of people use e-cigarettes throughout the day is not equivalent to a home. By the same token, a home where conventional cigarettes are smoked regularly receives not only exhaled smoke but also the continuous emissions from the burning tip of every cigarette.

Similar concentrations, therefore, do not necessarily reflect equivalent processes.

That distinction also emerges in the limited number of studies conducted in homes. In a pilot study, Derek Bush and Maciej Goniewicz collected surface samples from eight homes of e-cigarette users, six homes of cigarette smokers, and eight homes where no nicotine-containing products were reportedly used. Nicotine was detected on surfaces in half of the vaping households, compared with every smoking household. Average nicotine concentrations in the vaping homes were roughly 170 times lower.

The comparison with the control homes adds an important caveat.

Traces of nicotine were also detected in half of the homes where no one smoked or vaped, and average concentrations were not statistically different from those measured in the homes of e-cigarette users.

The authors suggested several possible explanations, including contamination left behind by previous occupants and nicotine entering through windows or ventilation systems, but they could not determine the source.

Because it was a pilot study, the lack of a statistically significant difference does not show that vaping cannot produce an indoor reservoir. It indicates that in this sample, the surface signal associated with vaping was small, variable, and difficult to distinguish from background contamination, and remained far below the levels observed in smokers’ homes.

The vape shop studies demonstrate that nicotine from e-cigarette aerosol can settle onto surfaces, accumulate under conditions of heavy use, and even migrate into neighboring spaces. They do not demonstrate that the same dynamics occur in bedrooms, living rooms, cars, or homes where emissions are less frequent and more dispersed.

The strongest conclusion the evidence supports is a modest one: nicotine from vaping can be detected on indoor surfaces. To establish a phenomenon comparable to third-hand smoke, researchers would still need to show that those residues persist, undergo meaningful chemical transformations, and produce exposure under ordinary, real-world conditions.

When a Molecule Becomes a Risk

By the end of the review, the question has narrowed: What does it mean for human health when residue from e-cigarette aerosol is found on a surface?

Studies show that nicotine can settle indoors and that, under certain conditions, some of its derivatives, including tobacco-specific nitrosamines, can be detected. Other experiments suggest that these residues may undergo further chemical change. Such findings establish chemical presence. On their own, they do not show that people receive a biologically meaningful dose.

That distinction has become more important as analytical methods have become sensitive enough to detect ever-smaller concentrations. Identifying a substance is one step. Estimating its possible health effects requires several others: determining whether it remains available for exposure, how it is transferred, by what route it enters the body, and how much is actually absorbed.

At each stage, some of the material may be lost, transformed, or rendered inaccessible. A concentration measured on a surface, therefore, does not translate directly into the dose a person receives.

Sussman’s review applies this logic to nicotine residues.

Beyond surface concentration, it considers the area of skin exposed, the duration and frequency of contact, body weight, and the fraction absorbed. A brief touch against a tabletop and repeated contact with a carpet may involve similar surface concentrations yet produce very different exposures.

Few studies have moved beyond environmental chemistry to examine biological effects. Those that have relied on mice.

Commodore and colleagues exposed thirteen animals for three weeks to towels previously contaminated with e-cigarette aerosol. Of eighteen inflammatory proteins measured in blood and bronchoalveolar-lavage fluid, two showed statistically significant differences: IL-7 was lower in the serum of exposed animals, while IL-13 was higher in fluid collected from the lungs. Most of the other markers, along with cellular counts, showed no clear differences. The study found a limited signal rather than a broad inflammatory response.

Thorpe and colleagues observed structural changes in the airways after four weeks of exposure to impregnated materials. The animals showed epithelial thickening, an increase in the number of cell layers, enlargement of alveolar spaces, and greater collagen deposition in the small airways. Nicotine worsened some of these changes but did not account for all of them. Histological evidence of increased alveolar space was also observed in animals exposed to residues from nicotine-free liquids, suggesting that other components of the mixture were involved.

Umphres and colleagues examined effects on platelets. Fabrics, carpeting, and upholstery samples were exposed to 400 puffs per day in 7-day cycles and then placed in the animals’ cages. Over the course of the four-month experiment, the materials were periodically replaced with newly contaminated samples. By the end, the animals’ platelets showed greater aggregation, secretion, and activation, along with features associated with an increased tendency toward thrombosis.

Together, the three experiments show that laboratory-generated residues can retain biological activity. They were also conducted under conditions of intense and repeated exposure. In the Commodore study, the animals came into frequent contact with towels contaminated by a vaping machine. In the Umphres experiment, they lived for months among materials exposed each day to hundreds of puffs. Thorpe’s study likewise relied on impregnated surfaces and repeated exposure.

These protocols are well suited to asking whether an effect can occur. They do not necessarily reproduce the intensity, frequency, or duration of exposure in an ordinary home. Nor do they permit a direct translation from effects observed in mice to effects in humans.

This is where the distinction between hazard and risk becomes essential.

The animal studies indicate that, given sufficient exposure, vaping residues can produce inflammatory, structural, and cardiovascular responses. Estimating human risk would require showing that comparable residues form in real environments, remain available for contact, and reach people at doses capable of producing similar effects.

A systematic review by Stracci and colleagues shows how small the field remains.

After searching five databases and retrieving 139 records, the authors found only three studies that met their inclusion criteria: the same three mouse experiments. Taken together, the studies suggested cellular and physiological changes associated with residues both with and without nicotine, but they did not support conclusions about harm in humans.

That does not establish safety. Nor does it establish a household risk. The literature consists of a handful of studies, small groups of animals, and protocols designed to generate measurable exposure. The absence of human studies does not rule out harm, but effects observed under these conditions cannot simply be projected onto the intermittent exposure typical of a home.

The available evidence supports three conclusions. Vaping residues can be detected on surfaces. Under certain conditions, they can persist, transfer, and produce biological effects in animals. What has not yet been shown is that ordinary household exposure delivers to humans doses capable of causing measurable harm.

When the Label Comes Before the Phenomenon

The term third-hand vaping entered the scientific literature by analogy with third-hand smoke. It then entered public discussion, often stripped of the nuances that had accompanied its introduction.

The logic was easy to follow. If cigarette smoke leaves behind persistent residues, and e-cigarette aerosol also carries nicotine, then it seemed reasonable to ask whether vaping might follow a similar sequence of emission, deposition, and subsequent exposure.

The analogy proved useful. It helped frame new research questions and brought together a growing body of studies on vaping residues. But it also implied an equivalence that still had to be established.

Different processes can share similar names without sharing the same persistence, chemistry, or potential for human exposure.

That, in Sussman’s view, is the central issue: the label may have arrived before the phenomenon itself had been fully characterized: the available evidence shows that nicotine from e-cigarette aerosol can reach indoor surfaces and that, under certain conditions, the resulting residues may undergo further chemical change. It does not yet show that deposition, persistence, transfer, and dose combine in everyday environments in a way comparable to what is observed with cigarette smoke.

That does not make the residues irrelevant. It means the category still rests on evidence that extends beyond detection alone.

The next generation of studies will need to determine how long these compounds remain available for exposure, how they move among air, dust, and indoor surfaces, by what routes they enter the body, and what doses they produce under real-world conditions.

There are sound reasons to minimize involuntary exposure to e-cigarette aerosol, particularly in enclosed spaces, during heavy use, and in the presence of young children or other vulnerable individuals. Devices, e-liquids, and patterns of use continue to evolve. None of those considerations, however, demonstrates that vaping residues behave like combustion residues or pose the same public health risks.

After the visible aerosol has disappeared, some of its components may remain on walls, fabrics, household dust, or even on a windowsill. What remains unknown is how long they persist, in what quantities, and with what consequences.

The evidence available today supports continued investigation and a cautious approach to involuntary exposure to e-cigarette aerosol.

But it supports prudence, not equivalence.

At present, it does not justify treating third-hand vaping and third-hand smoke as interchangeable phenomena.

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