Very hot drinks
Drinking tea, coffee or anything else scalding hot probably raises the risk of cancer of the oesophagus, the tube from throat to stomach. It is the heat, not the drink, and the best measurement puts the line at about 60 °C — but the human evidence is limited and comes mostly from places where this cancer is far more common than in Europe or the US.
Let a fresh cup stand a few minutes, about six in the one study that timed it, and drink it comfortably warm rather than scalding. That costs nothing and applies to every hot drink.
What the risk is
Repeatedly scalding the lining of the oesophagus is thought to be what does the harm, not anything in the drink itself. The cancer in question is oesophageal squamous-cell cancer, which grows from the cells lining the gullet.
The World Health Organization's cancer agency, the International Agency for Research on Cancer (IARC), classes the drinking of very hot beverages as "probably carcinogenic", and defines very hot as above 65 °C.[1] It based that on limited evidence in people and limited evidence in animals — the weakest grade of human evidence that still supports the classification. The studies behind it came from regions where tea or maté is traditionally drunk at about 70 °C, and found that risk rose with the temperature of the drink. The same review looked at coffee itself and moved it the other way, to "not classifiable", after reviewing more than 1,000 studies.
The study that measured the temperature
One study measured temperature directly rather than relying on self-report. In a cohort of 50,045 adults aged 40 to 75 in Golestan, northeastern Iran, trained staff measured the temperature of freshly poured tea at each person's interview, then followed them for a median of about ten years, during which 317 developed oesophageal squamous-cell cancer.[2]
- Temperature. Drinking tea at 60 °C or hotter carried 41% higher risk than drinking it cooler.
- Stated preference. People who said they liked their tea "very hot" had more than double the risk of those who drank it cold or lukewarm. The in-between "hot" preference showed no clear extra risk.
- Volume. People who drank 700 mL or more a day at 60 °C or hotter had about 90% higher risk than those who drank less, and cooler, tea. Smaller amounts that hot showed no clear extra risk, and the risk did not keep climbing above 700 mL.
- Waiting time. Drinking within two minutes of pouring carried about 50% higher risk than waiting six minutes or more.
The 60 °C line comes from this single cohort; IARC's 65 °C is its own approximation.
Why the numbers are smaller for most readers
These are relative risks, measured in one of the regions with the most oesophageal cancer in the world. There, the squamous-cell type makes up more than 90% of cases and the rate is 5 to 50 times higher than in Europe or the US. In Western countries most oesophageal cancer is a different type, adenocarcinoma, and the Golestan study was too small to say anything about it. A 41% rise on a small baseline is a much smaller absolute risk than the same figure in Golestan, and IARC notes that the share of oesophageal cancer caused by hot drinks is unknown. Neither the study nor IARC gives an absolute risk for hot tea.
That makes the evidence moderate at best: the direction is consistent, the size for a Western drinker is uncertain. The case for acting rests on the cost, which is close to nothing.
What to do
- Wait a few minutes after pouring — about six; in the cohort above, drinking within two minutes carried more risk than waiting six or more.
- Drink it comfortably warm, not scalding. If it hurts to sip, it is too hot.
- Take most care if you drink a lot of hot drinks a day, since the risk was clearest at high volumes drunk hot.
- Don't switch drinks over it. The risk is the temperature, the same for tea, coffee and maté.