Vape pens heat a liquid into an inhalable aerosol, delivering nicotine, cannabis compounds, or flavored vapor into your lungs. They’re battery-powered devices that work by electrically heating a small metal coil to temperatures between 200°F and 480°F, hot enough to vaporize liquid but below the point of combustion. What happens inside your body after you inhale depends on what’s in that liquid.
How a Vape Pen Works
Every vape pen has the same core parts: a battery, a small heating coil (called an atomizer), a wick, and a reservoir that holds liquid. When you press a button or simply inhale (some devices use a flow sensor), the battery sends current through the coil. The coil heats up, the wick draws liquid onto it, and that liquid turns into a fine aerosol you breathe in through a mouthpiece.
The vapor you see isn’t actually water vapor. It’s a mix of tiny suspended droplets created when the liquid reaches roughly 100 to 250°C (212 to 482°F) inside the heating chamber. Several factors shape what comes out: the electrical resistance of the coil, the voltage of the battery, how much airflow reaches the atomizer, and how efficiently the wick delivers liquid. Smaller, pen-style devices keep these variables fixed. Larger “box mod” devices let users adjust voltage and airflow to customize the experience.
What’s in the Liquid
At minimum, e-liquid contains two base ingredients: propylene glycol (PG) and vegetable glycerin (VG). These are the carrier fluids that produce the visible aerosol. Most liquids also contain nicotine and flavoring chemicals.
PG and VG do different things. Propylene glycol is thinner, carries flavor more effectively, and produces a stronger “throat hit,” that slight burning sensation in the back of your throat that mimics smoking. In controlled testing, liquids with a higher PG ratio (70% PG, 30% VG) were rated as having a significantly better throat hit than balanced or pure-VG blends. Vegetable glycerin is thicker and sweeter, and vaping culture widely credits it with producing denser clouds, though users in the same study didn’t actually rate cloud production differently between ratios.
Cannabis vape pens work on the same principle but use oil cartridges containing THC, CBD, or both instead of nicotine e-liquid. THC vaporizes optimally between 315 and 440°F, while CBD extracts fully at slightly different temperatures around 320 to 356°F. Some cannabis pens offer temperature settings so users can target different compounds.
What Happens in Your Body
When you inhale from a nicotine vape pen, the aerosol deposits nicotine onto the lining of your lungs, where it absorbs into your bloodstream and reaches your brain within seconds. Nicotine triggers a release of dopamine, producing a brief feeling of alertness and satisfaction. It also stimulates your sympathascular system, which is why you can feel your heart rate pick up.
The cardiovascular effects are measurable. A systematic review and meta-analysis found that a single vaping session raised heart rate by about 11 beats per minute, systolic blood pressure by nearly 13 points, and diastolic blood pressure by about 8 points compared to not vaping. For context, that heart rate jump was about 5 beats per minute less than what cigarette smoking produces, and the blood pressure increases were statistically similar between the two.
Nicotine formulation matters for how quickly these effects hit. Many modern pod-style vape pens use nicotine salts rather than freebase nicotine. Nicotine salts are smoother at high concentrations, which allows devices like JUUL to pack 5% nicotine into a small pod without an overwhelming throat burn. This makes it easier to inhale more nicotine per puff, which is one reason pod devices can be highly addictive, particularly for people who weren’t previously smokers.
What Else You’re Inhaling
The aerosol isn’t just nicotine and flavoring. The metal coil inside the atomizer can shed trace amounts of metals into the vapor. Lab analysis of e-cigarette aerosols has detected chromium, nickel, copper, zinc, tin, and lead at varying levels. Copper reached up to 614 nanograms and zinc up to 339 nanograms per 10 puffs in some devices. Chromium and nickel were found at levels equivalent to, or slightly above, those in conventional cigarette smoke. Cadmium, a particularly toxic metal, was below detection limits in all devices tested.
These are small amounts, but they accumulate with heavy daily use. The long-term effects of chronically inhaling low levels of these metals are still being studied.
The aerosol also affects the air around you. Indoor nicotine concentrations from vaping average about 3 µg/m³, roughly one-tenth the level produced by cigarette smoking in the same conditions. Fine particulate matter (PM2.5) from vaping averaged about 152 µg/m³ with human users, compared to 819 µg/m³ from cigarettes. Lower than cigarette smoke, but not zero, and well above outdoor air quality standards in most countries.
The EVALI Outbreak
In 2019, a wave of severe lung injuries linked to vaping swept across the United States. The CDC identified vitamin E acetate as the primary cause. This oily additive was used as a thickener in black-market THC vape cartridges. While harmless when swallowed as a supplement or applied to skin, inhaling vitamin E acetate interferes with normal lung function and caused life-threatening damage.
Cases peaked in September 2019 and declined sharply once the cause was identified and publicized. The CDC stopped actively collecting EVALI data from states in February 2020 but continues monitoring through emergency department surveillance. There has been no resurgence. The key takeaway from EVALI wasn’t that all vaping causes lung injury. It was that unregulated, black-market THC cartridges carried a specific and serious risk.
Which Products Are Legally Authorized
As of late 2025, only 39 e-cigarette products have received marketing authorization from the FDA through the premarket tobacco product application process. All of them are tobacco or menthol flavored. The authorized brands are JUUL, Logic, NJOY, and Vuse, each offering a limited selection of devices and pods or cartridges at set nicotine strengths.
Every flavored vape you see at a convenience store or gas station, whether it’s mango, watermelon, or blue raspberry, has not received FDA authorization. Many are sold in violation of federal law, though enforcement has been inconsistent. The absence of authorization doesn’t necessarily mean a product is dangerous, but it does mean it hasn’t gone through the FDA’s review of its health risks and potential benefits for adult smokers trying to switch.