Vapes contain more than just nicotine or cannabis. The liquid inside a vape typically includes a carrier base, an active drug, flavorings, and, depending on the product, a range of unintended chemicals that form during heating or leach from the device itself. Here’s what’s actually in them.
Nicotine: The Most Common Active Drug
The majority of vapes sold worldwide deliver nicotine. It comes in two chemical forms: freebase nicotine and nicotine salts. Freebase nicotine is the older formulation, typically ranging from 3 to 18 mg/mL in refillable devices. Nicotine salts, popularized by JUUL and similar pod systems, are chemically modified to feel smoother at much higher concentrations, commonly 20, 35, or 50 mg/mL. Some products go as high as 50 to 60 mg/mL.
The difference matters because nicotine salt formulations can deliver nicotine to the brain faster, making them more addictive. A single JUUL pod at 5% (roughly 59 mg/mL) contains about as much nicotine as a pack of cigarettes. Freebase nicotine above 20 mg/mL produces a harsh throat sensation that most people find unpleasant, which is partly why salt formulations dominate the high-strength market.
THC and CBD
Cannabis vape cartridges are the second major category. Legal THC cartridges sold in licensed dispensaries are concentrates, and they’re potent. In Washington State, concentrates averaged 69% THC in 2022, with some products reaching 90%. CBD-dominant cartridges also exist, though they’re less popular and less tightly tracked.
Illicit THC cartridges are a different story entirely. During the 2019 EVALI outbreak (a wave of severe lung injuries tied to vaping), the FDA and CDC identified vitamin E acetate as the primary culprit. It was used as a cheap thickening agent to dilute THC oil in black-market cartridges. About 50% of THC products tested by the FDA contained vitamin E acetate, and among patients who got sick, 81% had used cartridges containing it. Vitamin E acetate was found in the lung fluid of EVALI patients but not in healthy controls. The takeaway: unregulated THC cartridges can contain adulterants that don’t appear on any label.
The Carrier Liquids
Every vape liquid needs a base to dissolve the active ingredient and produce visible vapor. Nicotine e-liquids use propylene glycol (PG), vegetable glycerin (VG), or a blend of both. These are food-grade compounds considered safe to eat, but inhaling them repeatedly is a different question. When heated, PG and VG break down into irritating byproducts, which is covered below.
THC cartridges use different carriers. Legal products often use cannabis-derived terpenes or medium-chain triglyceride (MCT) oil. Illicit products have used vitamin E acetate, mineral oil, and other substances never intended for inhalation.
Flavoring Chemicals
Most vapes, especially those popular with younger users, contain synthetic flavorings. These can include dozens of individual compounds in a single product. The most studied concern is diacetyl, a buttery-tasting chemical linked to a serious lung condition called “popcorn lung” (bronchiolitis obliterans) in factory workers who inhaled it in large quantities. Related compounds like acetyl propionyl are also used and can actually convert into diacetyl over time. In lab testing, acetoin (another common flavoring) degraded into diacetyl at levels up to 8% of the original concentration, depending on the e-liquid’s formula.
Many manufacturers have removed diacetyl from their recipes, but enforcement is inconsistent, and flavoring formulas are often proprietary. Fruity and dessert flavors tend to contain the most complex chemical mixtures.
Toxic Byproducts From Heating
Even if an e-liquid starts out relatively clean, the heating process creates new chemicals. The most concerning are aldehydes: formaldehyde, acetaldehyde, and acrolein. All three are known irritants, and formaldehyde is a recognized carcinogen.
How much forms depends heavily on the device. A well-functioning, modern atomizer produced minimal aldehydes in testing: about 16.7 micrograms of formaldehyde per gram of liquid. But older or malfunctioning coils that overheat the liquid (producing “dry puffs”) can generate dramatically more. One study measured formaldehyde at 48,200 micrograms per gram under dry-puff conditions, roughly a 3,000-fold increase. Acrolein followed the same pattern, jumping from under 12 to over 10,000 micrograms per gram. Running a vape on high power with a dry or depleted wick is the main risk factor for high aldehyde exposure.
Heavy Metals From the Device Itself
The heating coil inside a vape is typically made of metal alloys containing nickel, chromium, and sometimes other elements. These metals leach into the liquid and vapor as the coil degrades. A 2025 study published in ACS Central Science tested popular disposable brands and found that chromium and nickel concentrations in the aerosol increased up to 1,000-fold over the life of a single device.
Some brands performed far worse than others. Esco Bar devices contained extremely high levels of lead (up to 175 parts per million), copper (up to 546 ppm), and zinc (up to 462 ppm) in both the liquid and the aerosol. ELF Bar and Flum Pebble devices produced lead levels one to three orders of magnitude lower, but still showed rising nickel and chromium as the coil wore down. Antimony, a toxic metalloid, appeared at high levels in both Flum Pebble and Esco Bar aerosols, reaching 2,300 micrograms per kilogram.
None of these metals are listed on any product label. You have no way to know how much metal a disposable vape is releasing unless it’s been independently tested.
Undeclared Pharmaceutical Drugs
In a smaller but disturbing category, the FDA has flagged e-liquids that contain undeclared prescription medications. Lab testing of products from a company called HelloCig found that an “E-Cialis” vape liquid contained both sildenafil and tadalafil (the active ingredients in Viagra and Cialis), while an “E-Rimonabant” product also contained sildenafil. These drugs can cause dangerous drops in blood pressure in people taking nitrate medications for heart disease or diabetes.
These products represent the extreme end of unregulated vaping, but they illustrate a broader point: without oversight, vape liquids can contain virtually anything.
What’s Actually Regulated
As of 2026, the FDA has authorized exactly 41 e-cigarette products for legal sale in the United States. These come from a handful of companies: JUUL, Vuse (R.J. Reynolds), NJOY, Logic, and Glas. Every authorized product is tobacco or menthol flavored. No fruit, candy, or dessert flavored vapes have received FDA authorization.
That means the vast majority of vapes on store shelves, particularly disposable flavored devices, are being sold illegally. They haven’t gone through the FDA’s review process, and their contents haven’t been independently verified. The authorized products aren’t risk-free, but they’ve at least been evaluated for what’s in them. Everything else is a question mark.