For the last decade or so there’s been a rumor going around that cold water is not as good for you as lukewarm or even hot water. You see these things floating around social media and it says that drinking cold water after a workout will “shock” your body. Or it will slow down your digestion and it isn’t as hydrating as other water temperatures. And that lukewarm water matches closer to the temperature of your actual body so it’s easier on your system. The problem with that rumor is that it’s wrong.
Cold water is essentially fine for you (we’ll get into the details later.) But the one type of water that everyone equates to super healthy is the one that actually can cause health issues. And not just any health issues, but cancer. And it’s not just us saying that it’s the World Health Organization (WHO.)
Very Hot Water Is the Only Drinking Temperature With a Cancer Classification
This all came about in June of 2016. That year a group of 23 scientists from the International Agency for Research on Cancer (IARC), which is an arm of the World Health Organization, found that extremely hot beverages had a likelihood of causing cancer in humans.
But how they came about this is the interesting part. This group of IARC scientists got together to find out if coffee (specifically coffee) was a carcinogen. They had called it a potential carcinogen in 1991 based on the mix of beans, chemistry, heat etc. But there were questions around that classification. So they pored over a thousand studies and found something much more concerning.
It wasn’t coffee that drew the warning, it was the heat. IARC classified the practice of drinking very hot beverages, above 65 degrees Celsius or about 149 Fahrenheit, as Group 2A — probably carcinogenic to humans — on limited evidence for esophageal cancer. Coffee itself went the other way, into Group 3, not classifiable, with the working group finding no conclusive evidence of a carcinogenic effect. That is a hazard classification of a habit, not a verdict that a cup one degree either side of 149 is safe or unsafe. Doesn’t matter if it’s tea, water, mate…anything.
– which is about 149 degrees Fahrenheit. “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,” said Dr. Christopher Wild then director at IARC.
The Study That Measured It Instead of Asking About It
An Iranian study is what provides the strongest evidence for the “hot beverages can cause cancer” theory.
Researchers in northeastern Iran followed over 50,000 people from the age of 40- to 75 for 10 years. In addition to the amount of people studied and the length of time, what was different about this study is they actually measured the temperature of what they were drinking. And they found that people who drank on more tea at higher temperatures And this is a region where esophageal cancer runs about 12 times the typical United States rate. The people who drank 700 ml a day or more at 60 degrees Celsius (140 Fahrenheit) or above had about a 90% higher rate of this cancer than people who drank less than that, cooler. That figure combines volume and temperature. Temperature on its own, 60 degrees and above against below it, carried a hazard ratio of 1.41 — and 60 degrees was the study’s upper cut point rather than a measure of “scalding.”
“However, according to our report, drinking very hot tea can increase the risk of esophageal cancer, and it is therefore advisable to wait until hot beverages cool down before drinking,” said Dr Farhad Islami of the American Cancer Society, the study’s lead author.
Does It Hold Up Outside Iran?
If you think that the Iranian study doesn’t equate as much to the US or western world because they have different teas, cultures etc, the US National Cancer Institute looked at 454,796 people in the UK. They followed them for over 11 years and found similar numbers to the Iranian study. The rates of esophageal squamous cell carcinoma were 2.5x at up to four cups per day, 3.7x for four to six cups, 4.8x for six to eight, and 5.6x above eight cups per day. Two things to keep straight about those figures: they count tea and coffee together rather than tea alone, and they belong to the people who said they preferred their drinks “very hot” — a stated preference, not a measured temperature — set against non-drinkers and warm-temperature drinkers.
The effect showed up for squamous cell carcinoma. For adenocarcinoma, the more common subtype in Britain and the United States, the paper reports that the hazard ratios “were not statistically significant nor did they show a clear pattern of higher risk with higher temperature and intake level.”
It is worth holding that next to what IARC said in 2016: “Smoking and alcohol drinking are major causes of oesophageal cancer, particularly in many high-income countries,” said Dr Christopher Wild, then the agency’s director.
The Four-Minute Rule
The same Iranian group also studied whether self reported waiting time corresponded to actual temperature. It did: self reported waiting time was more strongly associated with the measured temperature of the tea than self reported liking it hot. The study, published in 2009 in the BMJ, was a case control comparison of 300 people with esophageal squamous cell carcinoma and 571 neighbors without it in Golestan province, where almost everyone drinks black tea, with an average consumption of more than a liter a day.
Those drinking tea very hot had around eight times the odds of the cancer compared with those who drank it warm or lukewarm; those drinking it hot had around double. Measured in minutes it came out the same way. Those who waited 2-3 minutes to drink their tea had around two and a half times the odds of those who waited 4 or more minutes, while those who waited less than 2 minutes had more than five times.
That is the useful number, because nobody carries a thermometer. Freshly prepared tea is well above the 149-degree threshold. Four minutes on the counter, or a little cold milk, is the wait that moved people out of the high-risk group. Among the 48,582 people in the cohort whose tea temperatures were measured, about one in five drank it at or above the 65 degrees Celsius level of concern outlined by IARC. In a kitchen in America the proportion is probably lower, but those who drink tea or coffee fresh from the kettle or pot are probably still drinking it above 65 degrees Celsius.
Wouldn’t Big Tea-Drinking Countries Have Higher Rates?
The first question we had when we saw this data was, “Well, wouldn’t tea drinking countries like China, India and the UK have much higher rates of esophageal cancer?” And the answer, shockingly, was mostly yes!
According to epidemiologists, there is an esophageal cancer belt running from northeastern Iran through North-central China. In this area the cases of esophageal cancer run about twelve times that of the United States. China alone has about half of the world’s cases of esophageal cancer (this is in large part because of their large population, but also combined with their high rate of esophageal cancer.)
The one area that seems to be the exception is Britain. But there’s a likely reason. The Brits typically put cold milk in their tea, which likely cools it to below the 149 degrees. In China and Kashmir and Iran they drink their tea scaldingly hot. And there seems to be a real overlap between esophageal cancer and these super-hot tea drinking regions.
Now, making this comparison and relating it to only tea can be a bit misleading. Esophageal cancer can be caused by a wide range of other behaviors like alcohol use, smoking, air pollution and more. But it is interesting to add in hot tea drinking to that list.
Warm Drinks Do Something Real When You Are Sick
The benefits of drinking hot water when you have a cold or flu were revealed in research conducted at Cardiff University’s Common Cold Centre.
Scientists found that taking fruit cordial either warm (at 70 degrees C) or room temperature (around 20 degrees C), improved symptoms such as runny nose, cough and sneezing. Researchers at the centre also said that drinking hot water gave people relief from a sore throat, chilliness and tiredness.
The researchers involved were Sanu and Eccles. In their study of 30 individuals who had active cold or flu-like illness, they found no difference in measured nasal airflow between the two temperatures. What did change was how people felt: the hot drink gave immediate and sustained relief from runny nose, cough, sneezing, sore throat, chilliness and tiredness, while the room-temperature drink relieved only runny nose, cough and sneezing. “It is surprising that this is the first scientific research on the benefit of a hot drink for treating cold and flu symptoms,” said Professor Ron Eccles, director at Cardiff’s Common Cold Centre.
Room Temperature Is Fine, and That Is All It Is
Drinking room temperature water appears to have no significant downside, but also no measurable advantage over cold or warm water when it comes to hydration.
Brian Weiner, MD, a gastroenterologist quoted by Cleveland Clinic, puts the whole question in proportion.
“We all [need to hydrate] ourselves. That’s critical. In terms of studies or science about this, it is relatively limited,” he said.
The key word here is “water.” The temperature that gets you to actually drink water may not be optimal for digestion — but it will definitely get you hydrated, the same way other popular hydration drinks do. In other words: this is a preference question, not a physiology one.
How Hot Is the Cup You Were Just Handed?
Hotter than the cancer threshold, almost always. According to a 2008 paper in Burns by researchers looking for the safest temperature to serve coffee at, coffee is typically served at 160 to 185 degrees Fahrenheit. That is 11 to 36 degrees above the 149-degree line the WHO’s cancer agency drew, and hot enough that a spill causes a real scald, which is why burn researchers were interested in the first place.
The paper’s other finding is the one worth remembering. A panel of 300 coffee drinkers said they preferred to drink their coffee at about 140 degrees, give or take 15. Nobody wants to drink it at 180 degrees. It’s served piping hot because it looks and smells the way it should when it’s fresh from the coffee machine, not because that’s the temperature anybody wants to drink it at. Factoring in burn risk and taste, the Burns authors recommend serving coffee closer to 136 degrees.
So the cancer risk threshold sits inside the 40 degree gap between the temperature coffee is served at and the temperature people like to drink it at. As with tea, the answer is the same: the cup is too hot when it arrives, it cools into the range you prefer anyway, and letting it get there is the whole intervention.
Source: Calculating the optimum temperature for serving hot beverages, Burns 2008
The Short Answer
When it comes to hydration, drink whatever temperature works best. Drink cold water if you are exercising or enjoy it, and warm drinks when you’re sick. But don’t drink anything above about 149 degrees Fahrenheit.
The Temperatures That Actually Matter
Every figure below is measured in a published study. Sources are linked in each section.
| Temperature | What the research shows |
|---|---|
| Above 149°F (65°C) | Classified by the WHO’s cancer agency as probably carcinogenic to humans for oesophageal cancer |
| 140°F (60°C) and up | Drinking 700 mL a day or more at this temperature: 90% higher oesophageal cancer risk in a 50,045-person cohort, against less than that drunk cooler. Temperature on its own: 41% higher |
| Hot, cooled below 149°F | Relief from runny nose, cough, sneezing, sore throat, chilliness and tiredness in people with a cold |
| Room temperature | No measured downside, and no measured advantage over any other temperature for everyday hydration |
| 39°F (4°C), during exercise | Core temperature rose 0.83°C vs 1.13°C on room-temperature water; people also drank noticeably more of it |
| 36°F (2°C), ice cold | Fewer stomach contractions than 140°F water — and 19–26% lower food intake at the next meal |
“Cold Water Slows Digestion” — What That Actually Means
There’s some truth in the idea that cold water slows down digestion, though it comes with a caveat no one ever mentions when discussing the claim.
In an experiment run by researchers at Waseda University in Japan, 11 healthy young men drank 500 millilitres of water after having gone without food for ten hours. The participants were given three options: water that was either 2 degrees Celsius (about 36°F), 37 degrees C and/or 60 degrees C.
The researchers used ultrasound to monitor their stomachs during the experiment, which lasted one hour. At the end of it all, they reported:
“Consuming 500 mL of water at 2 degC suppressed gastric contractions and ad libitum energy intake compared with consuming 500 mL of water at 37 degC and 60 degC.”
In other words: drinking ice-cold water reduced stomach contraction frequency. In the same experiment, the men who drank it went on to eat 19 to 26 percent less at the following meal.
The limits of this experiment are obvious. The researchers only tested 11 men, not women; all the subjects were young and healthy; they consumed just one serving of water at each temperature.
This is not a weight-loss finding — and should not be sold as such. But slower digestion isn’t necessarily bad (though it may affect energy intake). There’s nothing in this study to suggest impaired digestion or absorption, nor that cold water causes fat solidification in your stomach — which are the claims that most people make when they repeat the “cold water slows digestion” meme.
During Exercise, Cold Water Is Simply the Right Answer
In one experiment, researchers measured how cold water affects core temperature during a training session, comparing water at 4 degrees Celsius against room-temperature water.
Drinking cold water prevented the rise in core body temperature by 0.83 degrees, compared with just 1.13 degrees in the room-temperature group. In fact, drinking chilled water delayed that rise by more than half an hour — while people drinking room-temperature water were already 15 minutes above baseline. There was no warm or hot water arm here: the comparison drink was 22 degrees Celsius.
Participants did not actually drink more of the cold water. The study prescribed a fixed volume, matched across both conditions, and intake did not differ between them. A separate experiment that did let people drink freely — eight men cycling in the heat, with drinks at 4 and 19 degrees Celsius — found 1.3 litres an hour against 1.0.
The results from the study were mixed: broad jump and time to exhaustion showed no significant difference, but bench press did. Cold water significantly reduced repetitions to fatigue (p = 0.046) — the one significant performance finding in the paper, and it ran against cold water. The defensible claim is that cold water blunted the rise in core temperature.
Does Cold Water Burn Calories?
Technically yes — but trivially so, and it does not matter. The most cited study comes from Boschmann et al (2003), who reported that drinking 500ml of water increased metabolic rate by 30%. In Brown et al’s 2006 replication with better equipment to detect small changes in energy expenditure, there was no thermogenic effect from room-temperature water. Cooling the water did produce a response, but it was small — “well below even the theoretical cost of warming the water up to body temperature” (Brown et al).
Weiner says: “I calculated it, and for every ounce of ice that you eat, it takes five calories to melt it and bring it up to body temperature.” This is about ice specifically. If cold water helps anyone’s weight loss effort, it’s because they drink more of it — which displaces something else — which is the whole logic behind most practical weight-loss advice.
Who Should Actually Be Careful With Cold Water
There are three groups, and they are narrower than the internet suggests.
If You Get Brain Freeze
In one population-based study (150ml ice-cold water delivered via straw), 7.6% of women — 51 out of 669 in the study — reported getting a headache, mainly after drinking the cold water. Those who had experienced migraine in the previous year were about twice as likely to have one.
In a 2020 cross-sectional survey of 618 adults — smaller than the study above, and a questionnaire about past cold-stimulus headaches rather than a drinking test — migraine did not raise the risk of brain freeze (odds ratio 1.17), though the pain was more intense in people with migraine or tension-type headache.
If You Have a Swallowing Disorder
If you have achalasia, the lower esophageal sphincter fails to relax properly and peristalsis is absent or ineffective, so there is no normal contraction pattern left for cold water to disrupt. In manometry done on achalasia patients specifically, cold water at 2 degrees Celsius raised resting sphincter pressure and prolonged contractions, making symptoms worse; water at 50 degrees lowered resting and residual sphincter pressure and shortened contraction duration.
In 29 achalasia patients, drinking a liter of water at 60 degrees Celsius the night before a peroral endoscopic myotomy — a therapeutic procedure, not a routine endoscopy — reduced retained food and improved preparation quality against matched controls. It’s the strongest evidence I’ve seen for any use of warm water (and it applies to one person out of every 100,000 per year).
If You Have Sensitive Teeth
And if you have sensitive teeth — why do we even need a study on that? People with exposed dentine are prone to “dentine hypersensitivity,” which is tooth pain triggered by cold food and drink.
A Note on “Thermal Shock”
“Thermal shock” is a materials-science term. It describes what happens to glass and ceramics. There is no clinical diagnosis by that name for drinking a cold beverage, and we could not find a source establishing one. What is real is narrower: cold-stimulus headache, the motility changes above, and dentine hypersensitivity in people with exposed dentine.
Swallow syncope (fainting after swallowing) has been documented but is rare. We were unable to find a reliable prevalence figure, so we’re not quoting one here.
So What Should You Actually Drink?
Drink whatever temperature you like — it still beats the drinks most people reach for instead. There isn’t much research to go on in this area.
If you’re working out or exercising regularly (and if I’m going to recommend anything here), drink cold water. It blunts the rise in your core temperature against room-temperature water, which is not the same thing as cooling you down faster, and the study behind that finding handed everyone the same amount to drink.
If you’re sick, drink warm water, and if you care what is in it, what it comes out of matters too —.
Tea and coffee should be cooled below 149 degrees Fahrenheit (65 degrees Celsius). When freshly brewed, tea is around 175–185 degrees Fahrenheit. If you wait a few minutes for the brew to cool down on the counter top, you’ll be fine. Or just add some cold milk.
And if you’re prone to headaches or have been diagnosed with a swallowing disorder like achalasia, skip the ice.
The Bottom Line
We spend so much time concerned about ice water, but not scalding tea.
This article is for general information and is not medical advice. Talk to your doctor about symptoms that persist.
Joseph has been writing and editing for a wide variety of publications over the last decade.
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