Children in Africa and parts of Asia are falling victim to an “invisible” epidemic—fungal toxins in food that can stunt their growth and delay their development, according to a new report from the International Agency for Research on Cancer and funded in part by the Bill & Melinda Gates Foundation. The two main toxins—aflatoxin and fumonisin—are present in dangerously high levels in groundnuts, cassava, and corn, which make up the bulk of children’s diets from Benin to Kenya.

The toxins have long been known to cause liver cancer and, in high enough concentrations, death. But this is the first time that they have been shown by multiple studies to contribute significantly to childhood stunting.

“It’s a massive problem” largely unknown in developed nations, says J. David Miller, a fungal toxicologist at Carleton University in Ottawa and one of the report authors. “Enormous amounts of money are spent [in the United States and Western Europe] to keep you from being exposed to these kinds of toxins.”

The toxins, byproducts of the Aspergillus and Fusarium fungi, are endemic in cornfields around the world. The difference is that U.S. and European producers do all they can to eliminate the contaminants to meet strict standards for human consumption—20 parts per billion (ppb) in the United States and just 2 ppb in Europe. Fields are heavily treated, and crops are processed so that any remaining toxins are leached out. Food that isn’t up to standard is used as animal feed or burned. Altogether, U.S. food producers spend between $500 million and $1.5 billion each year managing fungal toxins.

But in countries where food shortages are chronic, few farmers have the ability to treat their crops and enforcement is lax. The best-quality products are sold for export. “It makes me cry when I’m in Nampula in Mozambique and the women are there on the floor, sorting the grain by hand, trying to get the very best grain together and then send it to Europe,” says Peter J. Cotty, a plant pathologist with the U.S. Department of Agriculture’s Agricultural Research Service in Tucson, Arizona. “And it gets rejected by Europe. But it gets into the European bird feed market, which allows 50 [ppb], which no one in a developed nation would ever allow people to eat.”

People back home are stuck with food with even higher levels of toxicity—sometimes in the thousands of ppb.

Researchers aren’t certain about exactly how the toxins affect children, but the new report brings together six recent studies that show that children with high levels of toxin biomarkers in their blood are shorter and weigh less than other children their age. They also grow at a slower pace than their peers. Preliminary studies suggest the effects may have something to do with immune system activation and the way the body absorbs nutrients.

The report also lays out recommendations for controlling the problem, including treating fields with natural biocontrols, improving food storage conditions, and diet diversification. It also calls for the development of rapid screening methods that would be able to quickly detect the toxins in blood.

Miller says that the problem is as much social as scientific. “It just seems to be intractable for a whole variety of reasons,” he says. “If you look in the scientific literature, 50 years ago, public policy people said more or less exactly what we’re saying now. And here we are.”