The liquid used in a vaping device, commonly known as e-liquid or vape juice, is a mixture designed to create an inhalable aerosol. It consists of four main components: Propylene Glycol (PG), Vegetable Glycerin (VG), optional nicotine, and various chemical flavorings. While PG and VG form the bulk of the liquid, the lack of comprehensive transparency regarding the specific chemical composition of the final product is a major concern. The complexity of the chemical makeup, particularly the flavor compounds, combined with how these products are regulated and manufactured, creates a significant gap in consumer knowledge.
Regulatory Gaps and Inconsistent Oversight
The primary reason consumers lack full knowledge of e-liquid contents stems from the fractured and often slow pace of governmental regulation. In the United States, the Food and Drug Administration (FDA) classified e-cigarettes and their liquids as “tobacco products,” subjecting them to the complex and costly Pre-Market Tobacco Application (PMTA) process. This review requires manufacturers to prove their product is “appropriate for the protection of public health.”
This process places an immense financial burden on companies, especially smaller ones, slowing the toxicological review of thousands of products currently on the market. Consequently, the vast majority of e-liquids sold today have not been fully scrutinized by the FDA, leaving consumers dependent on manufacturer-provided information. Furthermore, this regulatory structure has not federally mandated comprehensive toxicological testing for all flavorings specifically for inhalation.
Jurisdictions outside the US often operate under different rules, creating a patchwork of quality standards across the globe. In the European Union, the Tobacco Products Directive (TPD) mandates that manufacturers notify authorities of new products and provide a detailed ingredient list and emissions data. This European approach requires more immediate disclosure than the US system, but still leads to varied scrutiny depending on the country.
This inconsistent oversight allows many products to enter the market without rigorous, standardized, inhalation-specific safety testing that would provide consumers with a clear picture of every inhaled chemical. The lack of a single, global standard for full ingredient disclosure and testing is a systemic challenge to consumer transparency.
Proprietary Formulas and Ingredient Secrecy
Even when manufacturers operate legally within existing regulatory frameworks, they have incentives to maintain secrecy over the exact chemical makeup of their products. A specific flavor profile, such as a complex fruit blend or a dessert taste, is considered a trade secret and a form of intellectual property. Manufacturers protect these formulas to maintain a competitive advantage in the market.
While base ingredients like PG, VG, and nicotine concentration are typically listed, the “flavorings” component is often grouped vaguely to protect the recipe. This single term masks a complex chemical mixture that can contain dozens or even hundreds of individual aromatic compounds. For example, a “strawberry” flavor is not a single compound but a balanced blend of esters, aldehydes, and other chemicals designed to mimic the natural taste experience.
Companies have legal avenues to protect these specific recipes. This legal protection, combined with a lack of a mandate for full public disclosure of every sub-component, allows manufacturers to keep these details confidential. Consequently, the consumer is left with a generic label that does not reflect the chemical complexity of what they are inhaling.
Unregulated Supply Chains and Illicit Products
A significant portion of unknown chemicals comes from products that completely bypass legitimate regulatory channels and quality control standards. This includes counterfeit e-liquids and black market products, which often contain unlisted and dangerous cutting agents. The health crisis known as E-cigarette or Vaping product Use-Associated Lung Injury (EVALI) highlighted this danger, with many cases linked to illicit products.
During the EVALI outbreak, investigators identified Vitamin E Acetate (VEA) as a culprit in the lung injuries. This substance, which is safe for consumption or topical application, was used as a thickening agent in illicit Tetrahydrocannabinol (THC)-containing vape cartridges. The highly viscous VEA was added to dilute active ingredients and increase product volume, thereby maximizing profits for illegal sellers.
These black market products operate without labeling requirements or quality assurance, meaning there is zero transparency for the consumer. Furthermore, Do-It-Yourself (DIY) mixing introduces uncertainty, as consumers may add unverified or unchecked ingredients to their e-liquids. The absence of quality control in these unregulated supply chains means the user has no way of knowing the identity, concentration, or safety profile of the final inhaled product.
Manufacturing Contaminants and Thermal Degradation
Even if an e-liquid’s label were accurate, the final aerosol inhaled can still contain unknown chemicals due to manufacturing contamination and thermal degradation. Contaminants can be introduced during manufacturing or leach into the liquid from the vaping device itself.
Heavy metals like tin, chromium, lead, and cadmium have been found in the aerosol, originating from the heating coils and other metal components. As the e-liquid is heated, it contacts these materials, which can shed trace amounts of metal particles into the vaporized mixture. The presence of these metals is a byproduct of the device hardware, not a listed ingredient.
The process of heating the liquid also causes thermal degradation, a chemical change that creates new compounds not present in the original e-liquid. When PG and VG are heated by the coil, they can break down through oxidation and pyrolysis. This reaction generates toxic byproducts, including carbonyl compounds such as formaldehyde, acetaldehyde, and acrolein. These compounds mean the final inhaled cloud is a complex mix of original ingredients and new, unlisted degradation products.