Toxic compounds produced by some fungi and among the most potent naturally occurring carcinogens for humans and animals. Aflatoxin intake is positively related to high incidence of liver cancer in humans in many developing countries. In many farm animals aflatoxin can cause acute or chronic diseases. Aflatoxin is a metabolic by-product produced by the fungi Aspergillus flavus and the closely related species Aspergillus parasiticus growing on grains and decaying organic compounds. There are four naturally occurring aflatoxins: B₁, B₂, G₁, and G₂. All of these compounds will fluoresce under a UV (black) light around 425–450 nm providing a qualitative test for the presence of aflatoxins. In general, starch grains, such as corn, are infected in storage when the moisture content of the grain reaches 17–18% and the temperature is 79–99°F (26–37°C). However, the fungus may also infect grain in the field under hot, dry conditions.