Vape oil, commonly known as e-liquid or e-juice, is the substance heated by an electronic cigarette or vaping device to create an inhalable aerosol. This complex mixture is designed to deliver substances like nicotine or cannabinoids without the combustion products found in traditional smoke. The exact composition of vape oil is highly variable, depending on the manufacturer, the intended use, and whether it contains flavorings or other specific additives. Understanding the liquid’s contents is necessary to grasp how vaping devices function and the potential effects of the inhaled aerosol.
The Primary Carriers: Vegetable Glycerin and Propylene Glycol
The foundation of nearly all vape oil is a blend of two main ingredients: vegetable glycerin (VG) and propylene glycol (PG). These food-grade compounds serve as carrier agents, making up the largest percentage of the liquid volume. Both are colorless, odorless liquids essential for vapor production and dissolving the other components.
Propylene glycol (PG) is a thinner, less viscous substance that acts as an effective flavor carrier. It provides a sensation known as “throat hit,” which mimics the feeling of inhaling traditional cigarette smoke. Due to its low viscosity, high-PG liquids work well in smaller, lower-wattage devices.
Vegetable glycerin (VG) is a thicker, slightly sweet liquid derived from plant oils. Its primary role is to produce dense, visible clouds of vapor. VG also offers a smoother, less harsh inhalation experience.
The specific ratio of PG to VG is chosen to influence the vaping experience. A balanced 50/50 blend offers both a good throat hit and moderate vapor production, appealing to users transitioning from smoking. Liquids with a higher VG content, such as 70% or 80% VG, are favored by users who prioritize large vapor clouds and a smoother inhale, typically using higher-wattage devices.
Active Components: Nicotine, THC, and CBD
Vape oil contains active components that determine the product’s primary effect on the user. Nicotine is the most common active ingredient in conventional e-liquids, serving as the addictive substance. It is measured and labeled in milligrams per milliliter (mg/mL) of liquid, with strengths ranging from 0 mg/mL up to 50 mg/mL.
Nicotine is delivered in two main forms: freebase and nicotine salts (nic salts). Freebase nicotine is the purest form but becomes harsh and irritating to the throat at higher concentrations due to its higher pH level. Nicotine salts are created by adding an organic acid, such as benzoic acid, which lowers the pH. This allows for much higher concentrations of nicotine to be inhaled with a smoother throat hit, facilitating faster absorption into the bloodstream. Nic salts are popular in small, high-nicotine-strength pod systems.
Vape oils can also contain cannabinoids, primarily tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is the psychoactive compound in cannabis, and its vape oils are concentrated extracts designed to produce a “high” sensation. These THC formulations are often thick and viscous, requiring specialized vaporization hardware. CBD vape liquids, derived from hemp, contain a non-psychoactive compound and are often marketed for therapeutic purposes. Unlike concentrated THC oil, CBD liquids are frequently formulated using a PG/VG base, making them thinner and compatible with standard vaping devices.
The Role of Flavorings and Other Additives
Flavorings constitute a significant portion of the non-carrier ingredients, with thousands of food-grade chemicals used to create a vast array of tastes. While these compounds are generally recognized as safe for ingestion, their safety when heated and inhaled into the lungs has not been fully established. The complexity and sheer number of these flavor chemicals make comprehensive safety testing challenging.
Certain flavor compounds have been identified as problematic when inhaled. Diacetyl, often used for a buttery or creamy flavor, has been linked to bronchiolitis obliterans, a severe and irreversible lung disease called “popcorn lung.” Acetyl propionyl, a common substitute for diacetyl, presents similar inhalation risks. Other additives, such as Cinnamaldehyde, which provides a cinnamon flavor, have been shown to act as a respiratory irritant.
Minor additives are sometimes included to modify the liquid’s properties beyond flavor. These may include small amounts of distilled water or alcohol to adjust viscosity, or sweeteners to enhance the perceived taste. The absence of comprehensive inhalation safety data for many of these additives raises questions about their long-term effects on lung tissue and respiratory health.
Toxic Byproducts and Contaminants
Even when vape oil is manufactured correctly, heating the liquid can generate unintended toxic byproducts and contaminants. A significant concern is the thermal decomposition of the PG and VG base liquids when heated to high temperatures, particularly above 470°F. This superheating can break down the carriers into volatile carbonyl compounds like formaldehyde and acetaldehyde, both classified as carcinogens. The degradation of PG can also produce acrolein, a potent respiratory irritant.
Contaminants can also leach into the aerosol from the vaping device itself. The metallic heating coils and components, often made of nickel, chromium, and other alloys, can degrade when exposed to the e-liquid and high temperatures. This process releases toxic heavy metals, including lead, nickel, and chromium, directly into the inhaled aerosol. Studies have found that nearly half of aerosol samples can have lead concentrations exceeding established health limits.
A particularly harmful adulterant identified in the vaping crisis of 2019 was Vitamin E Acetate. This compound is a viscous oil illegally added to illicit THC vape products as a thickening agent or diluent. When inhaled, Vitamin E Acetate deposits in the lungs. Its sticky nature is believed to be a strong factor in causing e-cigarette, or vaping, product use-associated lung injury (EVALI).