Vape juice contains four base ingredients — propylene glycol (PG), vegetable glycerin (VG), nicotine, and flavoring compounds. While PG and VG are FDA-approved for ingestion, their safety when heated and inhaled is a fundamentally different question. A 2024 review in Nicotine and Tobacco Research concluded that GRAS food-additive status "cannot serve as an indicator of the toxicity of e-cigarette ingredients when aerosolized and inhaled." This guide breaks down every ingredient, what happens whe