Vegetable glycerin (VG), also known as glycerol, is a simple polyol compound derived from plant oils, such as soy, coconut, or palm. This clear, odorless, and slightly sweet liquid is widely used across various industries. For decades, it has served as a solvent, moisturizer, and sweetener in pharmaceutical products, cosmetics, and a vast range of foods. However, the safety profile established for ingestion and topical application does not automatically extend to its modern use in e-cigarettes. The question of whether it is safe to inhale has become a major public health concern as its use in vapor products has grown rapidly.
The Role of Vegetable Glycerin in Vapor Products
Vegetable glycerin is one of two primary base ingredients in e-liquids, alongside propylene glycol (PG). VG is a trihydroxypropane molecule containing three hydroxyl groups, which contributes to its thick, syrupy consistency. This viscosity is directly responsible for the large, dense clouds of visible vapor that users exhale. VG is an effective humectant, meaning it attracts and retains moisture, a property that helps preserve the e-liquid’s flavor and extend its shelf life. When heated by the coil, VG rapidly converts into an aerosol, which acts as the carrier for nicotine and flavorings into the lungs. Most e-liquids blend VG with PG to balance vapor production and flavor intensity, but VG remains the main component for cloud creation.
Acute Respiratory Reactions to Inhaled VG
The immediate effects experienced after inhaling VG are largely attributable to its hygroscopic nature. As the VG aerosol enters the airways, it draws moisture from the surrounding mucosal surfaces, including the mouth, throat, and respiratory tract. This desiccation effect commonly results in short-term symptoms such as dry mouth and throat irritation. Users may also experience an increased urge to cough or a scratchy sensation in the throat.
For some individuals, this exposure can lead to transient changes in airway function, such as temporary airway constriction. While these effects are typically mild and resolve quickly, they represent the body’s acute reaction to the substance. Adequate hydration is often recommended to mitigate the discomfort. These acute symptoms are distinct from the potential cumulative damage that may occur with chronic inhalation.
Long-Term Data on Pulmonary and Systemic Safety
Research into the long-term safety of inhaling vegetable glycerin is still developing, but existing studies suggest potential cumulative effects on the respiratory system. Exposure to VG aerosols has been shown to induce inflammatory responses in lung cells in laboratory settings. Specifically, studies on human bronchial epithelial cells indicate that VG can increase the expression of inflammatory markers like IL-6 and IL-8. This suggests that chronic inhalation may contribute to a state of low-grade, persistent inflammation in the airways.
In animal models, repeated VG exposure has been linked to increased mucus concentrations and changes in lung tissue that resemble early stages of chronic lung disease. The aerosol can disrupt the normal function of the cystic fibrosis transmembrane conductance regulator (CFTR), a protein important for maintaining fluid balance in the airways.
Furthermore, VG is not an oil, which is a critical point regarding the risk of lipoid pneumonia. Lipoid pneumonia is caused by inhaling actual oil-based substances, a risk that VG does not inherently carry. However, the heating of VG and PG can produce other potentially harmful carbonyl compounds.
Beyond the lungs, chronic inhalation of vaping aerosols has also been associated with adverse cardiovascular markers, including elevated heart rate and impaired vascular function. These systemic effects suggest that the impact of VG inhalation extends beyond the respiratory system.
Official Regulatory Position and Research Gaps
The primary regulatory status of vegetable glycerin is “Generally Recognized As Safe” (GRAS), but this designation is strictly for its use as a food additive and does not cover inhalation. Major health organizations, including the U.S. Food and Drug Administration, recognize this distinction. The FDA has identified glycerol as a potentially hazardous chemical when used in tobacco products, highlighting the need for further scrutiny of its aerosolized form.
The fundamental gap in understanding the safety of inhaled VG is the lack of long-term human epidemiological data. Vaping is a relatively new phenomenon, meaning there are no multi-decade studies to assess the effects of chronic exposure on the lungs and other organ systems. Therefore, while laboratory and animal studies show clear biological effects, the long-term consequences for a typical user remain undetermined.