What Chemicals Are in Vapes? A Detailed Examination of E-Cigarette Ingredients

When people ask what chemicals are in vapes, the honest answer is: more than you think, and the list keeps growing as research catches up.

A lot of vapers assume they’re inhaling water vapor, nicotine, and some flavoring. That’s not even close. The aerosol from an e-cigarette contains the base ingredients, the nicotine, whatever flavor chemicals the manufacturer added, and then a whole second layer of compounds that form when those ingredients get heated to 200–400°C. On top of that, the device itself can shed metal particles into the vapor.

This article walks through each category, what we know, what we don’t, and what the most recent studies have found. Sources include the CDC, NCBI, Johns Hopkins Medicine, and several 2025–2026 peer-reviewed papers that have changed the picture considerably.

The four main chemical categories in vapes (see our ingredient breakdown for a consumer-focused explanation)

Every chemical you inhale from a vape falls into one of four groups:

Category	What it includes	When it appears
Base liquids	Propylene glycol (PG), vegetable glycerin (VG)	Present in e-liquid before heating
Nicotine	Freebase nicotine or nicotine salts	Added to e-liquid (0 mg options exist)
Flavoring chemicals	Diacetyl, benzaldehyde, ethyl maltol, benzoic acid, and hundreds more	Added for taste; varies by product
Thermal byproducts and contaminants	Formaldehyde, acetaldehyde, methylglyoxal, acrolein, heavy metals, VOCs	Form during heating or leach from device

The first three are what goes into the liquid. The fourth is what comes out when you use it. That distinction matters a lot.

Propylene glycol (PG): the carrier that doesn’t stay innocent

PG makes up roughly half of most e-liquid formulations. It carries flavor well and produces the “throat hit” that former smokers often want. The FDA classifies PG as “generally recognized as safe” for use in food and cosmetics. But eating PG and inhaling it after it’s been heated are different things.

A 2025 study from UC Riverside, published in Frontiers in Toxicology, changed the conversation. Researchers exposed lab-grown human airway tissue to realistic concentrations of two chemicals that form when PG is heated: methylglyoxal and acetaldehyde.

The findings:

• Methylglyoxal damaged mitochondria (the cell’s energy generators) and weakened the actin cytoskeleton at surprisingly low concentrations
• Acetaldehyde caused harm too, but required higher amounts
• Lower-powered devices , the kind people often assume are safer , may produce more methylglyoxal than higher-wattage setups

Prue Talbot, the study’s lead author, put it plainly: these are “signs of stress and injury that could contribute to long-term health problems if repeated during vaping.”

This is a big deal. PG is in nearly every e-liquid on the market. Until this study, methylglyoxal wasn’t part of the standard conversation about what chemicals are in vapes. Now it has to be.

Vegetable glycerin (VG): the cloud maker with its own problems

VG is the other base liquid, typically making up the other half of e-liquid. It produces the dense vapor clouds that vape users associate with satisfying hits. VG is also food-safe. For a breakdown of how VG thickness affects device compatibility, see our PG vs VG comparison.

When heated to high temperatures, VG breaks down into acrolein and formaldehyde. Acrolein is particularly nasty , it’s an irritant used as a herbicide, and it attacks the lungs directly. The amount formed depends heavily on device settings. “Dry puff” conditions, where the coil overheats because the wick is dry (keep your juice fresh with proper storage — see our vape juice expiration guide), can push formaldehyde levels close to those found in cigarette smoke (Nature, 2014).

Nicotine: addictive but not the carcinogen people think

Nicotine comes in two main forms in vapes:

• Freebase nicotine: the traditional form, used in older e-liquids. Harsher throat hit, slower absorption.
• Nicotine salts: formed by combining nicotine with an acid (usually benzoic acid). Smoother hit, faster absorption. Our nic salt vs freebase guide covers the differences in detail. This is what JUUL and most modern disposables use.

Nicotine is not classified as a carcinogen by itself. It drives addiction and may indirectly promote tumor growth by stimulating cell proliferation and blood vessel formation. It also affects adolescent brain development , memory, attention, and learning can all be impacted. The CDC is explicit: no nicotine product is safe for people under 21.

One thing people often get wrong: a typical disposable vape does not necessarily contain more nicotine than a pack of cigarettes. A standard 2ml device at 5% nicotine strength contains roughly 100 mg of nicotine total, but only about 20–40 mg is actually absorbed , comparable to one or two packs of cigarettes depending on usage patterns.

Flavoring chemicals: the wild card

This is where things get messy. Flavoring chemicals are the least regulated and most variable part of what chemicals are in vapes. A 2025 study in the Journal of Separation Science analyzing 60 disposable e-cigarettes found that ethyl maltol and benzoic acid appeared across almost all products, regardless of flavor or brand. Beyond those, the composition varies wildly.

Some flavoring chemicals of concern:

Diacetyl and acetyl propionyl (2,3-pentanedione) , Linked to bronchiolitis obliterans, commonly called “popcorn lung.” The condition is irreversible. While major manufacturers have largely removed diacetyl from their products, a 2025 study on flavoring stability found that some flavoring chemicals can degrade into other harmful compounds during storage and use, meaning the label might not tell the full story.

Benzaldehyde , Used for cherry and almond flavors. Irritates the respiratory tract. One study found it was present at significantly higher levels in cherry-flavored e-liquids than in unflavored ones.

Cinnamaldehyde , Found in cinnamon flavors. Research shows it can impair the function of immune cells in the lungs.

Vanillin and ethyl vanillin , Common in dessert flavors. These can react with PG during storage to form acetals, compounds whose inhalation toxicity has not been well studied.

The real problem: flavoring blends are proprietary. Manufacturers don’t have to disclose the full list. And as the 2025 flavoring stability study showed, the chemicals in the bottle can change over time, especially when exposed to heat and light.

Thermal byproducts: what forms when you press the button

This is the category most vapers don’t think about. The e-liquid is one thing. The aerosol you actually inhale is something else entirely.

Formaldehyde , Forms when PG and VG undergo thermal degradation. Under normal vaping conditions, levels are much lower than in cigarette smoke. But under dry-puff conditions, they can approach or even exceed cigarette levels. A 2025 study in Archives of Toxicology found that non-tobacco-flavored e-liquids produced different carbonyl profiles than tobacco-flavored ones, with some fruit flavors generating more formaldehyde per puff.

Acetaldehyde , Also forms from PG/VG degradation. The UC Riverside study showed it damages lung cells, though less severely than methylglyoxal at equivalent concentrations.

Methylglyoxal , the newly recognized threat , This is the finding that changed the landscape in 2025. The UC Riverside team found that methylglyoxal, which forms when PG is heated, may be more toxic to airway cells than acetaldehyde even at lower concentrations. It disrupts mitochondrial function and weakens cellular structure. Because nearly all e-cigarettes use PG, this applies to virtually every product on the market.

Acrolein , Forms primarily from VG degradation. A potent respiratory irritant. Even small amounts can cause coughing and airway constriction.

Heavy metals in vape aerosols

This is where the 2025 research from UC Davis really shifted the conversation.

A study published in ACS Central Science tested seven types of popular disposable e-cigarettes from three major brands. The results were alarming:

• Some devices released more lead in a single day of use than roughly 20 packs of traditional cigarettes
• Levels of chromium, nickel, and antimony increased the more puffs were taken
• Nickel levels in three devices and antimony levels in two devices exceeded cancer risk limits
• Four devices had nickel and lead emissions above health-risk thresholds for non-cancer effects (nerve damage, respiratory disease)

The metals came from two sources: leaded bronze alloy components that leached nickel and lead into the e-liquid, and degrading heating coils that released nickel directly into the aerosol. Antimony was already present in unused e-liquid at high levels.

Here’s the important context: these were illegal, non-FDA-approved disposable vapes. The kind sold in convenience stores and gas stations without regulatory authorization. Regulated, FDA-authorized products are held to different manufacturing standards. But the reality is that most disposable vapes on the US market are unregulated, and teens are the primary users.

How do vape chemicals compare to cigarette smoke?

This is the comparison people actually want. Here’s the honest breakdown:

Chemical	In cigarette smoke	In vape aerosol
Tar	Yes , major harm source	No
Carbon monoxide	Yes	No
Known carcinogens	At least 69	Trace amounts (formaldehyde, some metals)
Nicotine	Yes (20–30 mg absorbed per pack)	Yes (varies by device, 0 mg options available)
Heavy metals	Present (cadmium, lead, etc.)	Present (nickel, lead, chromium , higher in unregulated disposables)
Formaldehyde	High levels	Lower normally, can spike under dry-puff
Flavoring chemicals	Chemical additives	Diverse, partially undisclosed

The bottom line: regulated vaping products expose users to fewer toxic chemicals than cigarette smoke. No tar, no carbon monoxide, far fewer known carcinogens. But “fewer” is not “none,” and the 2025 research on methylglyoxal and heavy metals in disposables shows the gap may be smaller than previously thought, especially for unregulated products.

Regulation: what’s actually being done?

In the US, the FDA’s Premarket Tobacco Product Application (PMTA) process requires manufacturers to disclose ingredients and demonstrate that marketing the product is “appropriate for the protection of public health.” As of early 2026, only about two dozen e-cigarette products have received PMTA authorization. The vast majority of disposables on the market , the products most popular with young people , have not gone through this process.

In April 2026, the FDA proposed adding new constituents to its list of harmful and potentially harmful constituents (HPHCs) in tobacco products, which would require additional testing and disclosure.

The EU and UK take a different approach, capping nicotine strength at 20 mg/ml and limiting tank size to 2ml. They also require ingredient disclosure and have banned certain flavoring chemicals.

None of these regulations require full disclosure of thermal byproducts, which is a significant gap. The chemicals in the bottle are regulated. The chemicals that form when you heat them are not , at least not consistently.

What this means for you

Not sure which e-liquid is right for your device? Our guide to choosing your first e-liquid walks you through nicotine type, strength, and PG/VG ratio step by step.

If you vape, here’s what the current evidence suggests:

Know what you’re using. FDA-authorized products go through more rigorous testing than the unregulated disposables sold at gas stations. The UC Davis study showed that illegal disposables can release more toxic metals than cigarettes. Choose accordingly.

Understand that “food-safe” doesn’t mean “inhalation-safe.” PG and VG are safe to eat. Heating them and breathing the result is a different exposure pathway entirely. The methylglyoxal finding from UC Riverside underscores this.

Flavor matters. Not all flavors carry the same risk profile. Some generate more carbonyls when heated. Fruit and dessert flavors, in particular, showed higher formaldehyde production in the 2025 Archives of Toxicology study.

Avoid dry puffs. Running your device with a dry wick dramatically increases formaldehyde and acetaldehyde production. Keep your tank or pod filled.

If you don’t smoke, don’t vape. Vaping is a harm reduction tool for people who already smoke. It is not risk-free, and the long-term effects of inhaling these chemical combinations are still being studied. For more on this, see our guide to quitting vaping.

FAQ

What are the most harmful chemicals in vapes?
The most concerning are formaldehyde (a carcinogen formed during heating), methylglyoxal (newly recognized as highly toxic to lung cells, per the 2025 UC Riverside study), heavy metals like lead and nickel (especially from unregulated disposables), and flavoring chemicals like diacetyl (linked to popcorn lung).

Is propylene glycol safe to inhale?
PG is safe to eat, but inhaling it after heating is different. The 2025 UC Riverside study showed that heating PG produces methylglyoxal and acetaldehyde, both of which damage lung cells. Methylglyoxal was more toxic than acetaldehyde at lower concentrations.

Do all vapes contain the same chemicals?
No. The base ingredients (PG, VG, nicotine) are common to most, but flavoring chemicals vary widely. More importantly, thermal byproducts depend on device type, power settings, and usage patterns. Unregulated disposables have been shown to release higher levels of heavy metals than regulated products.

Can vaping chemicals cause cancer?
Some chemicals found in vape aerosol are known or probable carcinogens , formaldehyde and certain heavy metals, for example. The risk is lower than with cigarette smoke, but it is not zero. The long-term cancer risk from low-level exposure to these compounds over years of vaping is still being studied.

Are disposable vapes more dangerous than refillable ones?
The 2025 UC Davis study found that some illegal disposable vapes released more toxic metals (lead, nickel, antimony) than traditional cigarettes. Regulated refillable devices, which go through FDA’s PMTA process, are generally held to higher manufacturing standards. But the specifics depend on the product.

How many chemicals are in vape aerosol?
The exact number is unknown and depends on the product. E-liquids typically contain 4–20+ named ingredients, but thermal degradation and device contamination can produce dozens of additional compounds that don’t appear on any label. Some researchers using advanced analytical techniques have found previously unidentified volatile compounds in vape aerosol.

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Sources: CDC, FDA, NCBI, Johns Hopkins Medicine, UC Riverside/Frontiers in Toxicology (2025), UC Davis/ACS Central Science (2025), Journal of Separation Science (2025), Archives of Toxicology (2025), Federal Register (2026).