Answer: Corn Sweat

If you’re not from the Midwestern United States, there’s a very good chance that you think we’re pulling your leg, but we assure you we’re not. During the peak of summer heat in the Midwest, a significant contributor to the sweltering humidity is corn. Corn, well, sweating.

When it gets really hot outside, corn loses moisture via evapotranspiration—water discharge via tiny pores in the leaves. It’s pretty much the plant version of sweating. While all plants lose moisture in the heat (though plants adapted to arid climates lose very little), corn readily releases moisture when stressed by heat.

This factor, combined with the sheer volume of corn in the Midwest—there are 96 million acres of corn planted in the U.S. with the majority of it in the Midwest—actually raises the ambient humidity significantly. The phenomenon is called “corn sweat” and it can make days in July and August miserable in corn dense areas of the Midwest, highlighted in the USDA corn production map seen here.