Drinking very hot beverages 'probably' causes cancer of the oesophagus, global health experts warned today.
Gulping down anything very hot - over 65°C (150F) - including water, coffee, tea and other beverages - is linked to the disease, according The World Health Organisation's cancer agency.
The theory is that cancer can be initiated by constant irritation of the lining of the mouth and throat by very hot water.
'[New figures] suggest drinking very hot beverages is one probable cause of oesophageal cancer and that it is the temperature, rather than the drinks themselves, that appears to be responsible,' said Christopher Wild, director of the WHO's International Agency for Research on Cancer (IARC).
However, it concluded it is safe if consumed at 'normal serving temperatures' - i.e. 65 or under.
Previous research has suggested waiting at least four minutes before drinking a cup of freshly boiled tea, or more generally allowing foods and beverages to cool from 'scalding' to 'tolerable' before swallowing.
The IARC said: 'Studies in places such as China, Iran, Turkey and South America, where tea or mate is traditionally drunk very hot (at about 70°C) found the risk of oesophageal cancer increased with the temperature at which the beverage was drunk.'
'Drinking very hot beverages at above 65°C was classified as 'probably' carcinogenic to humans,' it added.
The agency reviewed more than 1,000 scientific studies on the possible cancer-causing properties of coffee, milky teas and the popular South American herbal infusion mate.
This is typically consumed from a closed container through a metal straw, delivering the brew directly to the throat.
But epidemiologist Dana Loomis, who took part in the review, said the same applied to any hot drink.
'It doesn't matter what the liquid is. What matters is the temperature,' he said.
The one study carried out on cold mate found no association with oesophageal cancer, the report said.
Some of the data pointed to 'significantly increased relative risks for drinking very hot tea and very hot beverages,' it found.
And in laboratory studies, very hot water at 65-70C boosted oesophageal tumours in mice and rats, said the agency.
He stressed this is 'really quite hot' - way above 'normal serving temperatures for coffee and tea in European countries and North America,' which are typically below 60 degrees.
The research had taken account of other lifestyle factors that could have skewed the data, such as participants' alcohol and tobacco use - high risk factors for oesophageal cancer.
But there is good news for coffee lovers, after the IARC has also ruled today the drink could help protect people from certain types of the cancer, such as womb and liver.
Both coffee and mate had been classified as 'possibly causing bladder cancer in humans' since 1991, when the last evaluation was conducted.
Since then, evidence has suggested neither drink could be linked to a higher risk of the disease, the agency said.
Instead, coffee will be reclassified in WHO rankings, meaning there is insufficient evidence to say it might even possibly cause bladder cancer.
It will move from Group 2B – in which substances are classified as 'possibly carcinogenic to humans' – into Group 3, for substances where there is no evidence of a link to cancer.
The studies took into account factors that could have skewed assessment of the cancer risk, such alcohol and tobacco use.
The IARC's ruling follows other recent research pointing to the health benefits of drinking coffee.
Last November, a study published in the scientific journal Circulation found that regular coffee drinkers had a lower risk of dying early from problems such as heart disease, diabetes and brain conditions.
Scientists reported that the many compounds in coffee are known to help lower inflammation or insulin resistance.
According to the WHO, cancer of the food pipe accounts for about 400,000 deaths out of eight million total cancer deaths every year.
Source: MailOnline