Hydrocarbon was found as the culprit that caused “off-flavor and smell” in cereal boxes that had to be recalled by Kellogg Co. last month. The presence of an aromatic hydrocarbon called methylnaphthalene reportedly caused nausea, diarrhea and vomiting.

28 million boxes of Apple Jacks, Corn Pops , Froot Loops and Honey Smacks cereal were recalled on June 25, and Kellogg Co. later confirmed that an elevated levels of hydrocarbons found in the package liners caused the off smells.

Methylnaphthalene is a petroleum-based compound approved by the FDA and it is found in the paraffin wax and film commonly used to coat foods including fruits and vegetables. The compound may leach into food like the case with Kellog’s cereal.

Although the compound is produced in large quantities in the U.S., according to the Environmental Working Group, little is known about the safety of hydrocarbon methylnaphthalene.