Ethoxyquin (EMQ) is a quinoline-based antioxidant used as a food preservative in certain countries and originally to control scald on pears after harvest (under commercial names such as "Stop-Scald").

[3] Ethoxyquin was initially registered as a pesticide in 1965 as an antioxidant used as a deterrent of scald in pears through post-harvest indoor application via a drench and/or impregnated wrap.

To date, the U.S. Food and Drug Administration has only found a verifiable connection between ethoxyquin and buildup of protoporphyrin IX in the liver, as well as elevations in liver-related enzymes in some animals, but no health consequences from these effects are known.

[11] In 1997, the Center for Veterinary Medicine asked pet food manufacturers to voluntarily limit ethoxyquin levels to 75 ppm until further evidence is reported.

The summary includes: loss of weight, changes in liver, kidney, alimentary duct, urinary bladder and mitochondria, anemia, lethargy, discolored urine, skin, or fur, increase in mortality, detrimental effect on immunity, condition factor of final body weight in relation to body length of fish and inducement of allergies (contact exposure).