What is corn sweat?
A phenomenon known as "corn sweat" can combine with summertime heat in the Midwest to make for some unbelievably humid conditions.
How corn sweat can make a heat wave feel so much worse
A phenomenon known as
The summer months can be downright brutal as temperatures soar and humidity rises, but it can be even worse in the Midwest thanks to an unusual phenomenon known simply as "corn sweat."
That’s not the technical term, but it’s a lot easier to just say corn sweat.
So, what is corn sweat and what does it do exactly?
How 'corn sweat' enhances the heat, humidity across the Midwest
FILE VIDEO - Nutrien AG Solutions meteorologist Andrew Pritchard joined FOX Weather on Wednesday morning to explain the science behind the phenomenon known as corn sweat and how it affects the heat and humidity in the Midwest.
"The technical term is in fact evapotranspiration," FOX Weather Meteorologist Marissa Torres said. "It occurs when you get large amounts of corn. I’m talking fields of corn that release a lot of moisture, which then increases the humidity levels."
If you grew up or are living in the Midwest, you’ve likely experienced it.
"Corn is a huge crop for the country, and the majority of that corn is grown where? In the Corn Belt, which includes Iowa, Illinois, Indiana, all the way east into even Ohio and as far north as Minnesota," FOX Weather Meteorologist Stephen Morgan said.
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This graphic explains the phenomenon known as "corn sweat."
(FOX Weather)
Corn (or any plant) pulls moisture out of the soil, and some of that moisture escapes through the corn's leaves and enters the surrounding air. This is called transpiration.
Just as humans sweat, or perspire, to cool down, plants are no different. The higher the air temperature, the more the plant will sweat, or transpire.
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This graphic explains the phenomenon known as "corn sweat."
(FOX Weather)
The transpired moisture will then evaporate off the plant's leaves to cool it down, just like how sweat evaporates off human skin. Evaporation is a cooling process.
Additional moisture also enters the air from lakes and other water sources in the area through evaporation. Combine all of this evaporation and transpiration, and you get evapotranspiration.
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This graphic explains the phenomenon known as "corn sweat."
(FOX Weather)
"So that crop, as it's really beginning to grow, those leaves and the plant itself is breathing," Morgan continued. "In fact, when it releases this water into the atmosphere, a single acre of the corn crop can release 3,000 to 4,000 gallons of water every day."
"Corn sweat" is simply a more colloquial way of referring to evapotranspiration in the vicinity of cornfields.
This graphic explains the phenomenon known as "corn sweat."
(FOX Weather)
This process of evapotranspiration leads to increased moisture in the air near cornfields as the corn "sweats" to keep itself cool, ultimately leading to higher dew points in many areas surrounding the cornfields.
Corn sweat to make expanding heat dome much, much worse
This graphic shows high temperatures and dew points in the Midwest on Wednesday, July 23, 2025.
(FOX Weather)
A massive heat dome is settling across the central and eastern U.S. this week, sending temperatures soaring into dangerous territory before the heat expands to the Northeast by the end of the week.
Before that, tens of millions of people from the Gulf Coast through the Midwest and into the Great Lakes region are under various heat alerts.
Temperatures in the Midwest are expected to range from the low 90s to upper 90s during the day on Wednesday.
This graphic shows the forecast heat index temperatures on Wednesday, July 23, 2025.
(FOX Weather)
However, extreme dew points due in part to corn sweat will make it feel even hotter.
The heat index is forecast to rise well above 100 degrees across the region, including cities in the Corn Belt like Des Moines in Iowa, Peoria in Illinois and Rolla in Missouri.