E-cigarettes contain artificial and other flavorings similar to those used in food and confectionery manufacture. The manufacturers often represent them to be safe. However, the US Flavor Extracts Manufacturers Association (FEMA) has pointed out, this safety relates to exposure through eating, and not inhalation. Also, the ingredients listed on the product labels for e-cigarettes rarely include the chemicals used for flavoring. The study revealed that high levels of these flavoring chemicals used in some brands of e-cigarette fluid could be respiratory irritants.

Researchers analyzed the levels and type of chemicals used to flavor e-cigarette fluid in a sample of 30 products in the US. They found that some brands of e-cigarette fluid exceed recommended exposure limits. The study authors said, "The results obtained are likely to be similar to what a broad survey would have revealed, and in any case, suggest that very high levels of some flavor chemicals are undoubtedly present in a great number of the thousands of products currently available."

The flavoring chemicals totaled more than 1% by volume in 13 of the 30 liquids analyzed, levels greater than 2% by weight in seven liquids, and levels greater than 3% by weight in two products. And many of the 'tobacco' flavored fluids contained chemicals used to flavor confectionery. The researchers said, "Six of the 24 compounds revealed in the analyses were aldehydes, compounds recognized to be primary respiratory irritants. Using a consumption rate of around five ml/day, as commonly reported on online vaping forums, vapers would be exposed to twice the recommended occupational exposure limits of benzaldehyde and vanillin with the products tested."