The visible cloud isn't the only thing e-cigarette users leave behind.
When electronic cigarettes first appeared, they were marketed as a "cleaner" alternative to traditional tobacco, producing harmless water vapor instead of toxic smoke. But what if the sleek devices and flavored vapors conceal hidden chemical exposures that affect both users and those around them? Scientists have turned to sophisticated biomarkers to uncover the truth about what really happens when someone vapes.
To understand e-cigarette exposure, researchers rely on specific biomarkers—measurable substances in the body that indicate exposure to particular chemicals. Two key biomarkers have become crucial in e-cigarette research:
Carbon monoxide (CO) in exhaled breath has long been used to assess exposure to combustible tobacco. CO binds to hemoglobin in blood, reducing oxygen delivery to tissues. It has a half-life of 5-6 hours in the body, meaning levels return to normal after 24-48 hours of not smoking 5 . Until recently, e-cigarettes were not thought to produce significant CO since they don't burn tobacco.
Urinary cotinine, a metabolite of nicotine, provides an objective measure of nicotine intake. Cotinine is preferred over measuring nicotine itself because it remains in the body much longer, with a half-life of 15-20 hours. This makes it ideal for detecting both active use and secondhand exposure 2 .
A revealing 2019 study from Turkey provides compelling data on what e-cigarette users actually absorb into their systems 1 . Researchers recruited twenty volunteer e-cigarette users to complete detailed questionnaires about their usage patterns, then measured both their exhaled carbon monoxide levels and urinary cotinine concentrations.
The research team followed a systematic approach:
The results revealed several unexpected patterns that challenged common assumptions about e-cigarettes:
| Characteristic | Findings | Percentage |
|---|---|---|
| Main reasons for e-cigarette use | To quit/reduce conventional cigarettes | 95% |
| Knowledge of health hazards | Recognized e-cigarettes as harmful | 15% |
| Awareness of addictiveness | Knew e-cigarettes are addictive | 45% |
| Nicotine content | Used nicotine-containing e-cigarettes | 100% |
Despite all participants using nicotine-containing devices, nearly half didn't know e-cigarettes are addictive, and only 3 people recognized they're harmful to health 1 .
| Biomarker | Median Level | Range | Notable Findings |
|---|---|---|---|
| Exhaled Carbon Monoxide (CO) | 3 ppm | 1-22 ppm | 25% of users had CO levels >7 ppm (typical smoker threshold) |
| Urinary Cotinine | 709.9 ng/mL | 318.6-825.3 ng/mL | All samples tested "positive" for cotinine |
The CO findings were particularly surprising. While median levels were low, the highest reading reached 22 ppm, and a quarter of participants exceeded 7 ppm—a threshold typically used to identify tobacco cigarette smokers 1 5 .
The researchers discovered a statistically significant correlation: participants who consumed more fluids daily had higher cotinine levels in their urine (r=0.511, p=0.025), suggesting possible differences in vaping frequency or style 1 .
The chemical emissions from e-cigarettes don't just affect the user. The environmental electronic vaping (EEV) aerosols can impact indoor air quality and expose bystanders 6 .
| Pollutant | Typical Levels During E-Cigarette Use | Comparison Context |
|---|---|---|
| PM₂.₅ (fine particles) | Up to 1,121 μg/m³ (above 150 μg/m³ in most cases) | 45× higher than WHO's 24-hour recommended limit |
| Ultrafine Particles | 7.2×10³ to 6.2×10⁴ particles/cm³ | Up to 20× higher than background levels |
| Airborne Nicotine | 2.59 μg/m³ (average in vape shops) | Detected in neighboring businesses at 0.17 μg/m³ |
Studies of vape shops show that e-cigarette usage significantly degrades indoor air quality, with particles traveling to adjacent businesses in multiunit buildings 6 . These findings raise concerns about secondhand and thirdhand exposure (from deposited residuals) for non-users in spaces where vaping occurs.
Bystanders inhale EEV aerosols containing nicotine, ultrafine particles, and volatile organic compounds.
Chemical residues settle on surfaces and can be re-emitted into the air or absorbed through skin contact.
When studying e-cigarette exposure, researchers rely on specific reagents and equipment:
Measures carbon monoxide in exhaled breath in parts per million (ppm); requires regular calibration and uses disposable mouthpieces for hygiene 1 5 .
Enzyme-linked immunosorbent assay kit that detects cotinine in urine or serum with high sensitivity; used to confirm nicotine exposure 1 .
Highly accurate method for quantifying total cotinine in urine after enzyme treatment; considered a gold standard 2 .
Precise method for measuring free cotinine in serum samples; used in large epidemiological studies 2 .
Used to normalize urinary cotinine measurements account for variations in urine concentration, making results more reliable 2 .
The Turkish study adds to growing evidence that e-cigarettes are not without risks. The unexpected production of carbon monoxide—traditionally associated with combustion—suggests the chemistry of e-cigarettes is more complex than initially assumed 7 . The fact that all users showed significant nicotine exposure through cotinine measurements confirms these devices effectively deliver this addictive substance 1 .
Perhaps most concerning is what these findings mean for vulnerable populations. With urinary cotinine levels rising among non-smokers in some countries despite tobacco control policies—possibly due to the spread of novel nicotine products—public health experts face new challenges 4 .
"Preventive strategies should be very strictly implemented for any tobacco products, including e-cigarettes, as they harm individuals and the community" 1 .
The chemical footprints don't lie—understanding what we're really inhaling and exhaling when using e-cigarettes is the first step toward making informed decisions about their use.