What is corn sweat? How Midwest crops are fueling summer humidity

What is corn sweat and why does it make the weather unbearable?

As dangerously hot weather is set to blister over Chicago this week, a Midwest-centric term "corn sweat" is making its rounds yet again.

CHICAGO - As dangerously hot weather is set to blister over Chicago this week, a Midwest-centric term "corn sweat" is making its rounds yet again. 

What is corn sweat?

What we know:

"Corn sweat" is a layman's term for the corn plant process known as transpiration. Like all plants, corn absorbs water through its roots, uses it to grow, and then releases the excess water as vapor to the atmosphere. With one plant or small groups, the effect on humidity is barely noticeable, if at all, but the Midwest has a different story.

The Midwest is home to millions of acres of crops, specifically, an estimated 11.1 million acres of corn in 2025. Those acres of corn are excellent at their one job – growing. 

What they're saying:

"Most plants don’t transpire a significant amount of water. Corn plants are really, really effective at transpiration," said Illinois State Climatologist Trent Ford.

So effective, that, according to Taranis, a crop intelligence platform, one acre of corn can release between "3,000 to 4,000 gallons of water every day during the peak growing season." 

Multiplied by the previously mentioned 11 million acres of corn, the amount of water vapor released equates to roughly 44 billion gallons of water daily during peak growing season in the summer.

The added humidity from the billions of water transpiration gallons can push the heat index even higher, making the weather feel significantly hotter.

Chicago is not only hit by this corn sweat, but also the warm and humid air from the Gulf of Mexico, making Chicago the sauna of the summer.

On the plus side, the mugginess of the corn sweat means the crops are growing, and the harvest should be healthy.