Love your drinks piping hot? It might be best to let them cool

That first steaming sip of tea or coffee may be comforting, but drinking beverages while they are still extremely hot could come with an unexpected health risk.

A large UK study has found that people who preferred their drinks “very hot” had about three times the risk of developing oesophageal squamous cell carcinoma (SCC) compared with those who drank them warm. Those who preferred “hot” drinks also had a higher risk.

The study, led by researchers at the University of Oxford and published in the International Journal of Cancer, analysed data from almost 980,000 adults and followed their health records for more than a decade.

The key point is that tea and coffee themselves were not found to be the problem. Rather, researchers believe repeated exposure to very high temperatures may damage the cells lining the oesophagus, the muscular tube that carries food and drink from the mouth to the stomach.

How hot is too hot?

The study did not record the exact temperature of every cup; rather, participants were asked whether they usually drank beverages warm, hot or very hot.

However, the International Agency for Research on Cancer, part of the World Health Organization, has previously classified beverages consumed above about 65°C as “probably carcinogenic to humans”.

That classification is based on evidence linking very hot drinks with oesophageal cancer in several parts of the world, including China, Iran, Turkey and South America.

Importantly, it is the temperature rather than a particular drink that appears to be responsible. IARC found no conclusive evidence that coffee itself causes cancer.

In the latest research, frequency mattered, too. After accounting for temperature, people who drank six or more hot beverages a day had a 71% higher risk of SCC than those consuming fewer than six, according to the researchers.

The association was specific to squamous cell carcinoma, one of the two main forms of oesophageal cancer, and was not seen for adenocarcinoma.

Why would heat matter?

The theory is fairly straightforward: repeatedly exposing the oesophageal lining to very hot liquids may cause small thermal injuries. Over time, repeated damage and repair may contribute to inflammation and changes that could make cancer more likely.

The experts are still investigating exactly how this process works, and the new study cannot prove that hot drinks directly caused the cancers observed.

One limitation is that participants described how hot they liked their drinks rather than having beverage temperatures measured objectively.

Muy-Teck Teh, professor of molecular oral oncology at Queen Mary University of London, told The Guardian that people may also differ in how they perceive or tolerate heat, making the relationship harder to interpret.

None of this means an occasional overly hot cup is likely to be dangerous. Cancer Research UK notes that oesophageal SCC remains relatively uncommon, so even a several-fold increase from a low underlying risk still leaves the absolute risk fairly small.

Smoking and alcohol are also well-established major risk factors for this form of cancer, and reducing those exposures remains more important for prevention.

For tea and coffee lovers, the practical advice is refreshingly simple. There is no need to give up your morning kopi or teh – just resist the urge to drink it while it is still scalding.

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