Vaping exposes you to fewer cancer-causing chemicals than smoking cigarettes, but it is not safe. E-cigarette aerosol contains significantly lower levels of most toxicants found in cigarette smoke, which is why some public health agencies have described vaping as roughly 95% less harmful than smoking. That figure, however, has drawn criticism for oversimplifying a complicated picture. The longer researchers study vaping, the more they find unique risks that cigarettes don’t share.
Fewer Toxicants, but Not Zero
Cigarette smoke contains over 7,000 chemicals, dozens of which are known carcinogens. E-cigarette aerosol contains far fewer. Tobacco-specific nitrosamines, a group of potent cancer-causing compounds abundant in cigarette smoke, are generally so low in e-cigarette aerosol that they fall below the threshold lab equipment can reliably measure. Formaldehyde, acetaldehyde, and acrolein (irritants and carcinogens present in smoke) also appear at substantially lower median levels in vapor.
The word “median” matters here. Formaldehyde levels in e-cigarettes vary enormously depending on the device. In open-tank systems, the difference between the highest and lowest formaldehyde concentrations spanned nearly a thousandfold when using the same liquid. Higher-power settings and dry coils push these numbers up dramatically. So while the typical puff delivers less formaldehyde than a cigarette, a poorly maintained or overheated device can close that gap.
Heavy Metals Are a Distinct Vaping Risk
One hazard that can actually be worse with vaping than smoking is heavy metal exposure. The heating coils inside e-cigarettes are made of metal alloys containing chromium, nickel, and iron. As the coil heats and degrades, those metals leach into the aerosol you inhale. A 2025 study analyzing popular disposable vapes found that some brands emitted 4 to 13 times more lead in their first 200 puffs than an entire pack of cigarettes. Copper and zinc concentrations were also elevated.
Not all devices are equal. Some brands tested at lead and nickel levels one to three orders of magnitude lower than the worst offenders. But a consistent finding was that metal concentrations increased as devices aged. In one popular disposable brand, chromium levels in the aerosol rose from 4 to nearly 2,000 micrograms per kilogram between the first 100 puffs and puff 1,500, while nickel climbed from 37 to 19,000. The longer you use a single disposable device, the more metal you’re likely breathing in.
Lung Health: Lower Harm Is Not No Harm
Studies comparing biomarkers in vapers, smokers, and nonsmokers tend to place vapers somewhere in the middle. One analysis found that e-cigarette users had biological profiles intermediate between never-smokers and cigarette smokers, suggesting reduced but real impact. Both smoking and vaping impair lung mechanics and cause oxidative damage in animal models, but the specific patterns differ.
E-cigarettes appear to trigger unique forms of lung stress. Flavored e-liquids in particular increased oxidative stress markers and immune cell counts in lung fluid beyond what unflavored liquids caused. PET imaging research found that e-cigarette users actually showed greater pulmonary inflammation than cigarette smokers in some measurements. And at the genetic level, while vapers and smokers share some patterns of immune gene suppression, vaping uniquely affects additional genes involved in airway defense and clearing debris from the lungs. The base liquids themselves, propylene glycol and vegetable glycerin, increased production of mucus proteins in airway tissue even without nicotine or flavoring added.
These findings don’t mean vaping is worse for your lungs than smoking overall. Cigarette smoke causes emphysema, chronic bronchitis, and lung cancer at well-documented rates. Vaping hasn’t been around long enough to know whether it causes the same diseases at the same frequency. What the research does show is that vaping is biologically active in the lungs in ways scientists didn’t initially expect.
Cardiovascular Effects Look More Similar
For heart and blood vessel health, the gap between vaping and smoking narrows. A study published in an American Heart Association journal reported that people who only used e-cigarettes had vascular stiffness and reduced blood vessel function similar to conventional cigarette smokers. Chronic users of both products showed comparable resting heart rate variability, a measure of cardiovascular stress. Animal studies confirmed that e-cigarette aerosol increased blood pressure and caused inflammation in blood vessels, the brain, and the lungs.
In mice, chronic e-cigarette exposure accelerated stiffening of the aorta and impaired the blood vessel lining’s ability to function properly. Researchers believe this likely leads to impaired heart function over time. The cardiovascular system, in other words, may not benefit as much from switching to vaping as the lungs do in terms of reduced carcinogen exposure.
Nicotine Delivery and Addiction Potential
Modern vapes deliver nicotine with remarkable efficiency. Around 2015, manufacturers began adding acids to nicotine to create “nicotine salts,” which reduce the throat burn and coughing that would normally limit how much nicotine a person can inhale. This made it possible to pack far more nicotine into a single device. A decade ago, a typical vape cartridge contained about the same nicotine as a pack of 20 cigarettes. Popular devices today can contain the equivalent of three cartons, or roughly 600 cigarettes, worth of nicotine.
This matters for addiction. Because vapes deliver nicotine so efficiently, dependence can develop quickly. For adult smokers trying to quit, that potency can be an advantage (more on that below). For anyone who doesn’t already use nicotine, especially adolescents, it creates a fast track to addiction that may be harder to break than earlier generations of nicotine products.
Vaping as a Quit-Smoking Tool
For current smokers, vaping does appear to help some people quit. In a large randomized controlled trial, 18% of smokers assigned to e-cigarettes achieved one-year sustained, biochemically verified abstinence from smoking, compared to 9.9% of those given traditional nicotine replacement therapy like patches or gum. E-cigarettes were also more cost-effective than patches and gum in that trial.
The catch is that most people who quit smoking with e-cigarettes continue vaping. Whether long-term vaping carries enough risk to offset the benefit of quitting cigarettes is still an open question, though most researchers agree that if you’re choosing between the two, inhaling vapor is less dangerous than inhaling smoke from burning tobacco.
Secondhand Exposure Is Much Lower
If you live with a vaper rather than a smoker, your secondhand exposure drops considerably. A study measuring air quality in homes across four European countries found that airborne nicotine in e-cigarette users’ homes was detectable but extremely low, averaging 0.01 micrograms per cubic meter. Fine particulate matter (PM2.5 and PM1.0), the tiny particles that penetrate deep into the lungs, was no different in vaping homes compared to control homes with no tobacco or vape use at all. Cigarette smoke, by contrast, is one of the most significant sources of indoor particulate pollution.
The 2019 Lung Injury Outbreak
In 2019, a wave of severe lung injuries linked to vaping hospitalized 2,668 people in the United States. The condition, called EVALI, was strongly linked to vitamin E acetate, an oily additive used as a thickener in illicit THC vape cartridges. The CDC identified vitamin E acetate as the primary culprit but noted that other chemicals in both THC and non-THC products could not be ruled out as contributing factors in some cases. Since the outbreak, legitimate manufacturers have avoided vitamin E acetate, and case numbers dropped sharply. The episode highlighted that what’s added to vaping liquid matters as much as the vaping itself, and that unregulated products carry outsized risk.
The Bottom Line on Relative Risk
Vaping almost certainly causes less harm than smoking cigarettes when it comes to cancer risk, respiratory disease burden, and secondhand exposure. The reduction in carcinogens is real and significant. But vaping introduces its own set of concerns: heavy metals leaching from heating coils, unique patterns of immune suppression in the lungs, cardiovascular effects that look uncomfortably similar to those from cigarettes, and nicotine delivery powerful enough to create rapid dependence. For a smoker who switches entirely to vaping, the trade is likely favorable. For a nonsmoker, picking up a vape means accepting a set of health risks that researchers are still working to fully define.