A 0-nicotine vape, often called nicotine-free e-liquid or vape juice, is a solution used in electronic vapor delivery systems that contains zero milligrams of nicotine per milliliter (mg/mL). Despite the absence of the addictive alkaloid, these liquids are complex chemical mixtures that require heat to create an inhalable aerosol. The liquid is a solvent base, which acts as the carrier for concentrated flavorings and other minor additives. Understanding what is contained in this solution involves examining the base liquids, the flavor compounds, and various unintentional components and byproducts.
The Base Liquids: Propylene Glycol and Vegetable Glycerin
The bulk of any e-liquid, including 0-nicotine formulations, is composed of two primary solvents: propylene glycol (PG) and vegetable glycerin (VG). These clear, odorless liquids are the foundation of the mixture, often accounting for 90% or more of the total volume. They dissolve the flavorings and are vaporized to create the visible aerosol cloud.
Propylene glycol is a thinner liquid that functions as an effective solvent for flavorings, carrying the taste more intensely than its counterpart. It is also responsible for the “throat hit,” a sensation similar to that experienced when inhaling traditional cigarette smoke, which many users seek. In contrast, vegetable glycerin is a thicker, slightly sweeter, sugar alcohol compound derived from vegetable oils. VG is prized for its ability to produce dense, voluminous clouds of vapor, contributing to a smoother, less harsh inhale compared to high-PG mixtures.
Both PG and VG are chemicals commonly used in food and cosmetics and are generally recognized as safe (GRAS) for ingestion by regulatory bodies. However, this designation applies to their consumption, not their safety when heated to high temperatures and inhaled deep into the lungs. The ratio of PG to VG is carefully balanced by manufacturers, as it dictates the final properties of the vapor, such as cloud production and flavor intensity.
The Role of Flavoring Compounds
Flavoring compounds represent the third major category of ingredients, typically making up 5% to 15% of the total e-liquid volume. These complex blends of chemicals, often artificial and synthetic, mimic a vast array of tastes, from fruits and desserts to beverages. While these flavorings are often food-grade, they have not been rigorously tested or approved for safety when inhaled into the lungs.
The chemical complexity of these blends is considerable, with some e-liquids containing up to 60 or more distinct flavoring agents. A particular area of concern has focused on a class of chemicals known as diketones, which are often used to create creamy, buttery, or custardy notes. Diacetyl is one such diketone that gained notoriety for its association with bronchiolitis obliterans, a severe, irreversible lung disease, after factory workers were exposed to high concentrations.
In response to these health concerns, some manufacturers began substituting diacetyl with similar compounds, such as acetyl propionyl. Research indicates that acetyl propionyl and other diketones may have a comparable safety profile when inhaled, posing similar risks to the respiratory tract.
Because these flavor formulations are proprietary, their exact chemical makeup can be difficult for consumers to ascertain, leaving users reliant on manufacturer claims regarding the absence of specific problematic ingredients.
Unintended Components and Byproducts
Beyond the intentionally added solvents and flavorings, the final aerosol contains substances not deliberately included in the liquid formulation. One source of these unintended components is the electronic hardware itself, particularly the metal heating coil (atomizer). As the coil heats the liquid, trace amounts of heavy metals can leach into the vapor and be inhaled.
Studies have detected various metals in the aerosol, including nickel, chromium, lead, manganese, and tin, which are released as fine particulate matter. A second source of unintended compounds is the chemical degradation of the base liquids due to high temperatures. When VG and PG are heated excessively, they can undergo thermal decomposition.
This process of thermal breakdown can generate toxic carbonyl compounds, such as formaldehyde, acetaldehyde, and acrolein. Formaldehyde, a known carcinogen, is a concerning byproduct of this thermal degradation. The formation of these aldehydes depends heavily on the device’s power settings and the temperature reached by the coil, distinguishing them as reaction products rather than initial liquid ingredients.