Drinking very hot beverages is “probably carcinogenic to humans,” according to a new assessment by the International Agency for Research on Cancer (IARC), which evaluates cancer risk factors for the World Health Organization. It defined “very hot” as over 150°F (65°C). This is the same classification the agency gave to red meat in late 2015.
In 1991 the Agency gave that classification only to one beverage—yerba maté, a tea infusion that is traditionally drunk very hot in South America. That was based on observational studies strongly linking high intake of maté to increased risk of esophageal cancer, presumably because the very hot temperature damages cells in ways that can promote tumors. Since then, additional animal experiments and observational human studies have suggested that any type of very hot beverage can increase the risk of cancer. The risk would come from long-term consumption of very hot beverages.
How hot is your coffee or tea? Probably not that hot by the time you drink it. Hot beverages are generally served at 160° to 185°F (71 to 85°C) in restaurants and cafes. At such temperatures, liquid can scald the mouth and, if spilled, skin. But the temperature quickly drops, depending on the delay before consumption, amount of liquid, thermal properties of the cup, and room temperature—plus the amount of milk, sugar, and whatever else you may add. Most people prefer temperatures of about 140°F (60°C) or less, according to some studies, and they usually wait until their beverages cool down to that range before drinking.
Also see Is Hot Tap Water Safe to Drink?