Vapes contain several ingredients that can damage your lungs, heart, and airways, and not all of them are obvious. Beyond nicotine, the base liquids, flavorings, metals from the heating coil, and chemical byproducts created by heat all pose distinct risks. Some are intentionally added, others form during use, and a few sneak in from the hardware itself.
Base Liquids: Propylene Glycol and Vegetable Glycerin
Every vape liquid starts with a base of propylene glycol (PG) and vegetable glycerin (VG). These are generally recognized as safe to eat, which is why they’re common in food. Inhaling them as an aerosol is a different matter. A 2024 study published in Scientific Reports found that seven days of exposure to PG/VG aerosols, with no nicotine or flavoring added, triggered airway inflammation in human bronchial cells. The aerosol ramped up production of inflammatory markers and caused the airways to produce thicker, stickier mucus while simultaneously impairing the channels that keep mucus properly hydrated.
That combination is similar to what happens in chronic obstructive lung diseases. The same study confirmed these findings in living animals: sheep exposed to PG/VG aerosol showed increased mucus concentration and elevated enzyme activity associated with tissue breakdown. The takeaway is that even a “plain” vape with no nicotine or flavoring still delivers an aerosol that disrupts normal airway function.
Flavoring Chemicals and “Popcorn Lung”
The flavors that make vapes taste like mango, vanilla, or caramel come from food-grade chemicals that were never tested for inhalation safety. The most well-known offender is diacetyl, a buttery flavoring linked to bronchiolitis obliterans, commonly called “popcorn lung.” The name comes from a cluster of cases in the early 2000s where workers at microwave popcorn factories developed irreversible scarring of the tiny airways in their lungs. Some cases were severe enough that lung transplant was the only remaining option. Exposure levels as low as 0.2 parts per million were associated with fixed airway obstruction in those workers.
When researchers tested 51 flavored e-cigarettes, they found diacetyl in 39 of them, including fruit, candy, and cocktail flavors marketed to younger users. The process of heating and vaporizing these chemicals creates an inhalation pathway strikingly similar to the one that harmed factory workers. Two related compounds, 2,3-pentanedione and acetoin, were also detected and carry similar concerns.
Heavy Metals From the Heating Coil
The metal coil that heats your vape liquid leaches toxic metals directly into the aerosol you inhale. Most coils are made from alloys containing iron, chromium, aluminum, and nickel. A study in Environmental Health Perspectives measured metal concentrations at three points: in the liquid as it comes from the manufacturer, in the tank after sitting on the coil, and in the aerosol itself. The results showed dramatic increases after coil contact. Nickel concentrations jumped from a median of about 2 to over 68 micrograms per kilogram between the fresh liquid and the tank. Chromium and aluminum followed the same pattern.
Lead was especially concerning. It isn’t even a listed component of most heating coils, yet median lead concentrations rose from about 0.5 in the dispenser sample to nearly 15 in the aerosol and over 40 in the tank. Lead likely exists as a trace contaminant in the metal alloys. Chromium, nickel, and lead are all established toxic metals, and manganese and zinc, also detected, are harmful specifically when inhaled.
Vitamin E Acetate
Vitamin E acetate was the primary culprit behind the 2019 EVALI outbreak (e-cigarette or vaping product use-associated lung injury) that hospitalized thousands of people in the United States. It was used as a thickening agent in illicit THC-containing vape cartridges to make the product look higher quality while cutting costs. Investigators found it in 49% of THC product samples linked to EVALI cases.
The substance damages lungs in two ways. Its molecular structure allows it to penetrate the thin layer of surfactant that lines your air sacs, disrupting the surface tension your lungs need to inflate properly. When heated in a vape device, it can also break down into ketene, a reactive gas that irritates lung tissue. Vitamin E acetate is not typically found in regulated nicotine vapes, but it remains a risk in black-market THC cartridges and unregulated products.
Synthetic Cooling Agents
Many mint- and menthol-flavored vapes use a synthetic cooling agent called WS-23 instead of actual menthol. It’s also added to non-menthol flavors to mask the harshness of nicotine and other chemicals, making the vapor feel smoother. Research published in Toxicology Reports found that WS-23 aerosol exposure increased MUC5AC expression in airway cells, a marker of excess mucus production, and induced goblet cell hyperplasia, meaning the airways grew more mucus-producing cells than normal. That kind of remodeling can impair airway function over time and increase susceptibility to respiratory disease. WS-23 is largely unregulated in vaping products.
Toxic Byproducts From Heat
Heating propylene glycol and vegetable glycerin doesn’t just turn them into vapor. It breaks them down into toxic aldehydes: formaldehyde, acetaldehyde, and acrolein. Formaldehyde is a known carcinogen. Acrolein is particularly relevant to heart health because it triggers oxidative stress in blood vessels, activates platelets (increasing clot risk), and damages HDL cholesterol, the “good” cholesterol that protects arteries. These effects raise theoretical concerns about long-term cardiovascular disease, though the concentrations produced during normal vaping may be lower than those needed to cause clinical harm. The catch is that higher voltage or temperature settings increase the production of these chemicals substantially, so users running devices at high power are exposed to more.
Ultrafine Particles
Vape aerosol isn’t just flavored water vapor. It contains ultrafine particles measuring between 6 and 26 nanometers, small enough to bypass your upper airways entirely and reach the alveoli, the deepest part of your lungs where oxygen enters the bloodstream. During a 20-minute vaping session in a moderately sized room, particle concentrations increased roughly sixfold. These nanoparticles can carry the metals, aldehydes, and flavoring chemicals described above deep into lung tissue, and potentially into the bloodstream. This matters not only for the person vaping but also for anyone nearby breathing secondhand aerosol.
Nicotine in Salt Form
Nicotine itself is the most familiar harmful ingredient. Pod-based devices like JUUL use nicotine salts, which are nicotine combined with benzoic acid to lower the pH and reduce throat irritation. This allows manufacturers to pack dramatically higher concentrations into each puff without the harshness that would make freebase nicotine at the same level unpleasant. A single JUUL pod contains roughly 50 mg/mL of nicotine, which is two to ten times the concentration found in most conventional e-cigarettes and equivalent to about 20 combustible cigarettes worth of nicotine.
The lower pH of nicotine salt means nearly all of the nicotine is in its protonated form (about 304 out of 308 millimoles per liter in JUUL, compared to roughly 44 out of 148 in a freebase device like Blu). Protonated nicotine absorbs more smoothly through the airways, which is why salt-based pods deliver a fast, cigarette-like nicotine hit that is especially effective at creating dependence. For younger users who start with these devices, the high concentration and efficient delivery make addiction more likely and harder to break.