Researchers have identified cytotoxic flavor chemicals in top-selling electronic cigarette refill fluids, raising concerns about potential respiratory health risks. Studies have found high concentrations of these flavor chemicals in e-cigarette liquids, and are working to quantify and assess their toxicity. The chemical composition of e-cigarette aerosols is being compared to that of traditional cigarette smoke, with some studies also exploring the impact of e-cigarette aerosols on human cells.