How Corn Sweat Is Causing Midwest Fields To Turn Up The Heat This Summer

Every summer in the Midwest, residents brace themselves for not only sweltering temperatures but something a bit more mysterious – a stifling heat that seemingly sticks to the skin. But that is much more than the imagination; it might actually be corn sweat. As strange as it sounds, this real and powerful phenomenon, known scientifically as evapotranspiration, actually plays a key role in driving up humidity. That’s especially true during the dog days of summer. And with people becoming more knowledgeable about the country’s agricultural industry, this important issue has gotten more attention. But what exactly is corn sweat and why is it turning fields of corn into giant humidifiers? Let’s break down the science, scale and quirky facts behind one of nature’s most bizarre weather contributors. 

What is corn sweat?

Corn sweat is the nickname for evapotranspiration, which is a natural process, as The Smithsonian describes. During this process, plants (but corn in particular), release water vapor into the atmosphere. And as corn grows, it absorbs water through its roots and moves it up through its stalks and leaves. But this moisture eventually escapes through the leaves’ tiny (plant) pores.

These are called stomata, and they help the moisture to enter the air as water vapor. So when temperatures rise and the surrounding air becomes dry, corn basically does what humans do: it sweats. It does so to cool itself down and maintain internal hydration, a survival mechanism. 

Why does corn sweat matter? 

In the Midwest, where corn is king and fields stretch for miles, the overall effect of this transpiration (or sweating) can be significant. This process is estimated to push localized humidity levels higher than surrounding areas. This phenomenon creates an overall Midwestern mugginess, which may feel familiar to some people. Per The Smithsonian, “For context, farmers planted 91.5 million acres of corn in 2024, of which only about 20 percent is grown for human consumption. […] Most of the country’s corn is used in animal feed and ethanol-based fuels.”

Despite the term sounding like a joke, corn sweat is a pretty serious concern for people and agriculture generally. Meteorologists actually take corn sweat pretty seriously when calculating summer heat waves. That is particularly true in agricultural regions like Indiana, Iowa and Illinois. 

How much does corn sweat a day?

Believe it or not, an acre of mature corn can release between 3,000 to 4,000 gallons of water per day, as The University of Illinois College of Agricultural, Consumer & Environmental Sciences confirms. At peak perspiration, that number can hike up to 5,000 gallons of water per day being released into the atmosphere during summer heat. Multiply that by thousands of acres across the Corn Belt, that’s equivalent to billions of gallons of water vapor being released into the air each day.

As The Herald-Times reports, although that number seems pretty high, it’s less than expected. In fact, “An inch of rainfall, by comparison, introduces about 27,000 gallons of water to an acre of land.” So, although it may be expected that this phenomenon would make the weather feel more manageable, like rain, there are serious matters to consider. 

This massive output of moisture doesn’t just affect nearby crops; it alters local weather patterns. It often raises dew patterns and pushes the heat index. So overall, it impacts how the weather and heat often feel well above the actual temperature. During some Midwestern heatwaves, the lingering nighttime humidity, which often feels oppressive, is attributed to corn sweat. Unlike regular heat, this humidity does not even go away when the sun sets, making it harder for people and the environment to cool down overnight. 

Is corn sweat good?

The answer to this question is a bit complicated from an agricultural standpoint. Corn sweat is a sign of healthy crops, since it shows that the corn plants are actively regulating their temperature and absorbing water and nutrients properly. Transpiration also helps plant tissue not to overheat and ultimately supports photosynthesis. This is critical for growing strong, productive ears of corn.

However, from a human perspective, corn sweat is not exactly ideal. The additional moisture it dumps into the air can make already hot conditions feel unbearable. This is particularly true when people already deal with stagnant air or high-pressure systems like a heat dome. 

High humidity makes it harder for the human body to cool itself through perspiration. This increases the risk of things like heat exhaustion or heatstroke. As The Smithsonian confirms, “High humidity exacerbates the health risks of extreme heat, which is the leading cause of weather-related deaths in the United States and a growing concern in a changing climate.”

Corn sweat also keeps temperatures elevated overnight, reducing the relief naturally provided by cooler evenings. So, while corn sweat is great for the plant and those looking to enjoy it, it can make life miserable for those nearby during a heatwave.   

Frequently Asked Questions

What is the real name for corn sweat?

The technical term for corn sweat is evapotranspiration, a combination of terms, per Ohio State’s College of Food, Agricultural, and Environmental Sciences. It is a mix of the word evaporation, which is water rising from the soil, and transpiration, water released by plants. So while corn sweat is a cool nickname, evapotranspiration is the process responsible for the phenomenon. 

What does corn sweat smell like?

Many people describe the smell of cornfields in the summer as sweet, earthy and slightly musty. So the smell isn’t offensive. But it is distinctive and might even trigger nostalgia for anyone raised around agriculture. 

What is the hairy stuff on corn called?

The silky threads on the top of an ear of corn are called corn silks, as the Nebraska Corn Board reports. These play a crucial role in reproduction for corn, since each silk connects to a potential kernel and must be pollinated. Though these are unrelated to corn sweat, they are another quirky feature of corn that adds to its uniqueness.