Vapes are battery-powered devices that heat a liquid solution (e-liquid) to create an aerosol for inhalation. E-liquid typically contains nicotine, propylene glycol, vegetable glycerin, and flavorings. When inhaled, the nicotine is vaporized and delivered rapidly into the respiratory system. The amount of nicotine absorbed into the bloodstream, known as its bioavailability, is highly variable. This variability depends on a complex interplay of chemical, physiological, and behavioral factors, meaning the actual nicotine dose can fluctuate significantly.
The Mechanism of Nicotine Absorption
Nicotine in the inhaled aerosol bypasses the digestive system and is primarily absorbed through the vast surface area of the lungs. The lungs contain millions of tiny air sacs, called alveoli, which allow for extremely rapid transfer of nicotine directly into the arterial bloodstream. This blood then carries the nicotine quickly to the brain.
The physical and chemical state of the nicotine determines its absorption efficiency. Nicotine exists in two forms: freebase (unprotonated) and salt (protonated). Freebase nicotine is more volatile and readily crosses the lipid membranes of the lung tissue, making it highly bioavailable. Nicotine salts, created by adding an acid, are less harsh on the throat even at high concentrations.
Nicotine salts permit the formulation of e-liquids with much higher concentrations, sometimes exceeding 50 mg/mL. This higher concentration, combined with smaller aerosol particle size, allows for a greater total amount of nicotine to be absorbed quickly. The smoothness of nicotine salt aerosols enables users to take deeper, longer puffs without the throat irritation of high-concentration freebase nicotine.
Factors Determining Nicotine Intake from Vaping
The actual dose of nicotine absorbed is governed by three main categories of variables: the e-liquid, the device, and the user’s behavior. Nicotine concentration in the e-liquid, expressed in milligrams per milliliter (mg/mL), directly influences intake. The ratio of propylene glycol (PG) to vegetable glycerin (VG) also plays a role, as higher PG content often results in increased nicotine yield in the aerosol.
The characteristics of the vaping device are important in determining absorption. Devices with higher power settings and lower coil resistance generate more heat, which aerosolizes more e-liquid per puff. This increased vapor production delivers a higher nicotine yield, sometimes resulting in a significant dose even with a lower concentration e-liquid. High-powered devices using a low concentration liquid can deliver more nicotine than lower-powered devices using a high concentration liquid.
The user’s puffing behavior, often called puff topography, directly controls the amount of nicotine inhaled. Puff duration, frequency, and the depth of inhalation are all variables that a user can adjust. Individuals can “titrate” their nicotine intake by taking longer or more frequent puffs to achieve their desired effect. Longer puff durations are consistently associated with a greater increase in plasma nicotine levels.
Comparing Vaping Absorption to Traditional Cigarettes
The speed and peak concentration of nicotine delivery from vaping differ significantly from traditional cigarette smoking. Cigarettes deliver a rapid, high-peak dose of nicotine, often achieving a maximum plasma nicotine concentration (\(C_{\text{max}}\)) of 15 to 20 nanograms per milliliter (ng/mL) within 2 to 5 minutes (\(T_{\text{max}}\)). This rapid spike contributes significantly to the addictive potential of cigarettes.
Early, lower-powered e-cigarettes struggled to deliver comparable nicotine, resulting in a much lower \(C_{\text{max}}\) and a much slower \(T_{\text{max}}\). Newer generations of advanced vaping systems, particularly those using nicotine salts, have dramatically improved delivery. These modern devices can achieve a \(C_{\text{max}}\) of 10 to 12 ng/mL, with a \(T_{\text{max}}\) of approximately 5 to 7 minutes.
While advanced devices narrow the gap, the average nicotine delivery from vaping still tends to be slower and lower than that of a combustible cigarette. However, the ability of modern vapes to deliver a rapid, high dose means some users can achieve plasma nicotine levels comparable to smoking. This is especially true when using high-nicotine salt liquids and modifying puffing behavior.
Nicotine Metabolism and Excretion
Once absorbed into the bloodstream, nicotine is rapidly processed by the body, primarily in the liver. The liver enzyme cytochrome P450 2A6 (CYP2A6) converts most of the nicotine (approximately 70 to 80%) into its main metabolite, cotinine.
Nicotine itself has a relatively short elimination half-life, typically lasting only about two to 2.5 hours. Cotinine, the major metabolite, is much more stable and serves as a reliable, long-term biomarker for nicotine exposure. Cotinine has a significantly longer half-life, ranging from 12 to 20 hours in most individuals.
Because of its stability, cotinine levels in blood, urine, or saliva are often measured to quantify a person’s overall nicotine exposure over several days. The body slowly eliminates cotinine and other minor metabolites through the kidneys. These byproducts remain detectable in the body for several days following the last use.