Late July in the Midwest has always been hot, but this week, the region is drenched in a whole new level of sticky, stifling heat — and a major reason behind that suffocating humidity is something called “corn sweat.” Yes, it’s real. And no, it’s not pleasant.
Corn sweat refers to the moisture that cornfields release into the air during hot, sunny days. Just like people perspire to cool off, plants transpire — pulling water from the soil and pushing it into the atmosphere. This release of moisture, combined with evaporation from the ground, is called evapotranspiration.
In regions like Iowa, where corn dominates the landscape, this process intensifies during summer heatwaves. Add a massive heat dome — like the one currently gripping much of the United States — and the humidity skyrockets. That makes the air feel thicker, hotter, and more oppressive, with heat index readings climbing well above 110°F (43°C) in several spots.
It’s not that corn plants sweat more than other types of vegetation — an acre of oaks, for instance, can release more water. But what sets the Midwest apart is the sheer density of farmland. In Iowa, over two-thirds of the state is agriculture, and corn is the most common crop. Soybeans, which also release moisture, follow closely behind.
According to Bruno Basso, an expert in crop science at Michigan State University, this combo of high heat and extra humidity from the cornfields is dangerous. It raises the risk of heat-related illnesses, especially for outdoor workers, the elderly, and anyone lacking access to air conditioning.
Strangely, evapotranspiration is also supposed to have a cooling effect — much like how forests feel cooler than parking lots. But during extreme heat, those dynamics shift, says Basso. The added humidity can cancel out that natural cooling and trap heat overnight, robbing people of much-needed relief.
One study from 2020 by researchers at the Harvard-Smithsonian Center for Astrophysics found that croplands in the Midwest — particularly areas covered in corn — can push moisture levels in the air up by as much as 40 percent during summer heatwaves.
That kind of spike in humidity doesn’t just make you sweat more — it affects how your body cools down, how crops grow, and how the local climate functions.
Historically, much of this land was covered in native prairie, which Basso says managed moisture better thanks to its diverse plant species with varied root depths. Today’s monocultures of corn and soybeans, by contrast, suck up water quickly and release it all at once, which not only fuels the mugginess, but may also worsen drought conditions by draining soil moisture faster — even if the Midwest is expected to see more rainfall in the coming decades.
So, next time you’re drenched in sweat walking through southern Minnesota or eastern Nebraska, you might just be feeling the effects of millions of acres of corn working overtime — pumping moisture into the sky, one stalk at a time.
