Patulin is a mycotoxin produced by a variety of molds, in particular, Aspergillus and Penicillium. It is commonly found in rotting apples, and the amount of patulin in apple products is generally viewed as a measure of the quality of the apples used in production. It is not a particularly potent toxin, but a number of studies have shown that it is genotoxic, which has led to some theories that claim that it may be a carcinogen, though animal studies have remained inconclusive. Patulin is also an antibiotic. Several countries have instituted patulin restrictions in apple products. The World Health Organization recommends a maximum concentration of 50 µg/L in apple juice.