In recent years, e-cigarettes have quickly become popular around the world due to their "harm reduction" concept and rich flavors. However, lagging market supervision has led to the proliferation of inferior e-liquids, among which the problem of excessive harmful substances such as formaldehyde and heavy metals is particularly serious. In 2023, the US FDA's random inspection showed that 23% of the commercially available e-liquids had excessive formaldehyde, while the China Consumers Association report pointed out that the heavy metal content of some e-cigarettes exceeded the national standard by more than 5 times. This article will deeply analyze the health threats of inferior e-liquids and provide practical identification methods.