Warning: Very Hot Drinks May Cause Cancer

Remember when McDonald’s lost a lawsuit over a customer accidentally scalding herself with too-hot coffee? The temperature of that spilled coffee was between 180 to 190 degrees Fahrenheit, causing third-degree burns that required skin grafts for the customer’s inner thighs. Besides a burnt tongue or lap, there’s another reason why very hot drinks might be harmful to your health.

While official serving recommendations for tea, hot chocolate and coffee is between 160-185 degrees, you’ll probably want to wait a few moments to let these liquids cool before sipping. Turns out, drinking hot beverages above 149 degrees might cause cancer.

Back in June, the World Health Organization’s International Agency for Research on Cancer (IARC) published a study in the Lancet Oncology classifying “very hot beverages”—149 degrees or above—under Group 2A, meaning that such drinks are "probably carcinogenic to humans," after reviewing data suggesting a link to esophageal cancer.

Rudolf Kaaks, an epidemiologist at the German Cancer Research Center in Heidelberg told Science that the link is plausible. Kaaks, who previously worked for IARC, explained that scalding hot water can cause inflammation, which is known to increase cancer.

As it happens, 149 degrees Fahrenheit is probably hotter than any coffee, tea or hot chocolate you might consume in the U.S. Home-brewed coffee is usually served around 140 degrees, and when I asked my local Starbucks barista, she said their coffee is exactly 135 degrees.

But in places such as China, Iran, Turkey and South America, tea or maté (a traditional, caffeine-rich South American drink made by steeping dried leaves of the yerba maté plant) is traditionally consumed around 149 degrees or hotter.

“Maté is not only prepared very hot, but drunk through a metal straw that delivers it directly into the throat,” IARC’s Dr. Dana Loomis told the Guardian. (I can also confirm that as a Chinese person, my family has sent back tongue-burning teas and soups at restaurants for being too tepid.)

“It appears that there is thermal injury from exposure to hot liquids that is capable of leading to cancer of the esophagus,” Loomis added.

IARC director Christopher Wild explained that while smoking and alcohol drinking are major causes of esophageal cancer particularly in many high-income countries, “the majority of esophageal cancers occur in parts of Asia, South America and East Africa, where regularly drinking very hot beverages is common and where the reasons for the high incidence of this cancer are not as well understood.”

Hot drinks now belong in the same 2A cancer group as red meat, high-temperature frying and various chemicals.

The same IARC study also determined that drinking coffee itself was not classifiable as carcinogenic to humans, a reverse of the organization’s 1991 decision. So coffee lovers need not worry—just avoid drinking your morning cuppa’ joe above 149 degrees.

"These results suggest that drinking very hot beverages is one probable cause of esophageal cancer and that it is the temperature, rather than the drinks themselves, that appears to be responsible,” Wild said.

We doubt you’ll bust out a thermometer for each cup, but if you’re consuming hot drinks at home or in a restaurant, the rule is that a drink is safe “basically, when your tongue says it is” for coffee, and “when you can hold the cup in your hand without being burned” for tea.

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