Aflatoxins are toxic metabolites produced by a variety of molds such as Aspergillus flavus and Aspergillus parasiticus. Aflatoxins have been associated with various diseases, such as aflatoxicosis. They are carcinogenic and can be present in grains, nuts, cottonseed, crops and other commodities associated with human food or animal feeds. This discovery has led to a growing awareness of the potential hazards of these substances as contaminants of food and feed causing illness and even death in humans and other mammals. these studies also revealed that there are four major aflatoxins: B1, B2, G1, G2 plus two additional metabolic products, M1 and M2, that are of significance as direct contaminants of foods and feeds.

Contamination happen when cows are fed with contaminated feed aflatoxin B1, B2, G1, G2, then aflatoxin B1 is converted by hydroxylation to aflatoxin M1, which is subsequently secreted in the milk of lactating cows. Aflatoxin M1 is quite stable towards the normal milk processing methods such as pasteurization and if present in raw milk, it may persist into final products for human consumption. Most controlling government agencies worldwide have regulations regarding the amount of aflatoxins allowable in human and animal foodstuffs. Many countries have declared limits for the presence of aflatoxin M1 in milk and milk products. In the EU the limit for the presence of M1 in milk and reconstituted milk powders has been set at 0.05 mg/L or 50 parts per trillion (50 ppt.)