The EPA classifies PBO as a group C carcinogen - "possibly carcinogenic to humans." Under the auspices of the United Nations, the Food and Agriculture Organization/World Health Organization (FAO/WHO) Joint Meeting on Pesticide Residues evaluated the entire body of toxicology of PBO several times since 1965. They concluded that, at doses up to internationally accepted standards for a maximum tolerated dose, PBO is not considered to be carcinogenic in the mouse or rat, thus leading to the conclusion that PBO is not carcinogenic to humans.[15]