Ice water is not harmful for most healthy people. It won’t damage your organs, freeze your stomach, or cause any lasting health problems. That said, cold water does produce some real, measurable effects in the body, and a few specific groups of people may want to stick with room temperature or warm water instead.
What Happens When Cold Water Hits Your Stomach
Your stomach is roughly 98.6°F (37°C). When you drink ice water at around 39°F (4°C), your stomach temperature drops temporarily, reaching its lowest point about 45 seconds after you start drinking. In a study of healthy volunteers, this cold temperature slowed the initial rate at which the stomach emptied its contents compared to body-temperature water. The effect was directly correlated with how much the temperature inside the stomach dropped.
This is the grain of truth behind the popular claim that ice water “hurts digestion.” But the slowdown is temporary. Your body warms the water quickly, and gastric emptying returns to its normal pace. For a healthy person eating a typical meal, this brief delay has no practical consequence. You won’t absorb fewer nutrients or experience digestive problems from drinking cold water with food.
Cold Water and Headaches
If you’ve ever gulped ice water and felt a sharp pain in your forehead, you’re not alone. In a study of 669 women, about 7.6% developed a headache after drinking just 150 milliliters (roughly five ounces) of ice-cold water through a straw. The more notable finding: women with active migraines were twice as likely to get these headaches compared to women who had never experienced migraines. Women whose migraines were “inactive” (no episodes in the past year) had no increased risk.
The mechanism is similar to brain freeze from ice cream. Cold hitting the roof of your mouth triggers referred pain in the forehead. For most people, it’s brief and harmless. But if you deal with frequent migraines, drinking very cold water quickly could provoke a headache episode.
Effects on Heart Rate
Ice water triggers a mild activation of the vagus nerve, which connects your brain to your heart and gut. In healthy subjects, drinking ice water produced a small but statistically significant decrease in heart rate and a shift toward parasympathetic (rest-and-digest) nervous system activity. Room temperature water did not produce the same effect.
For healthy people, this is harmless. Your heart rate dips slightly, then normalizes. But this vagal response is the reason ice water has historically been questioned for patients recovering from heart attacks, where sudden changes in heart rhythm are a concern. If you have a known heart condition, it’s worth being aware of this effect.
Nasal Congestion and Mucus Flow
One area where cold water performs measurably worse than warm water is nasal mucus clearance. In a study of 15 healthy subjects, sipping cold water reduced the speed at which mucus moved through the nasal passages, dropping from a baseline of 7.3 millimeters per minute to 4.5 millimeters per minute 30 minutes later. Hot water, by contrast, increased mucus velocity significantly when sipped (from 6.2 to 8.4 millimeters per minute), though that benefit also faded within 30 minutes.
This doesn’t mean cold water causes colds or infections. But if you’re already congested from a cold or allergies, ice water could temporarily make you feel more stuffed up, while warm liquids will help things flow more freely.
Tooth Sensitivity
If you’ve ever winced while drinking ice water, the issue is almost certainly in your teeth rather than any broader health problem. Beneath your tooth enamel sits a porous layer called dentin, filled with microscopic channels that lead to the tooth’s nerve center. When cold water hits, the dentin contracts and expands rapidly, causing fluid in those tiny channels to shift and trigger a pain signal.
Healthy enamel insulates dentin from temperature changes. But if your enamel has thinned from acidic foods, aggressive brushing, or natural wear, or if you have small cracks in a tooth, cold water reaches the dentin more easily. Ice water doesn’t damage enamel on its own, but it will reliably expose sensitivity that’s already there.
Who Should Actually Avoid Ice Water
For one group, ice water causes a genuinely significant problem. People with achalasia, a condition where the esophagus can’t move food properly into the stomach, experience worsened symptoms from cold beverages. In a study of 12 achalasia patients, 9 reported discomfort from cold food and drinks, including increased difficulty swallowing and regurgitation. Cold water increased pressure in the lower esophageal sphincter and prolonged the duration of esophageal contractions, essentially making it harder for food and liquid to pass through. One patient even developed esophageal spasms.
People with esophageal motility disorders are the clearest case where avoiding ice water makes a real difference. For everyone else, the effects are minor and temporary.
Cold Water During Exercise
If there’s a scenario where ice water is actually preferable, it’s during a workout. In an exercise study, participants drinking cold water experienced a core temperature rise of only 0.83°C over the session, compared to 1.13°C for those drinking room temperature water. The cold water group also delayed any increase in core temperature for 30 minutes, while the room temperature group saw a rise after just 15 minutes.
That said, the temperature advantage didn’t translate into significant improvements in power, endurance, or jump performance in moderate conditions. The researchers noted cold water likely offers the most benefit during exercise in hot, humid environments or over longer durations. Still, if staying cool during a workout matters to you, cold water gives a measurable edge.
The Calorie-Burning Claim
You may have heard that drinking cold water burns extra calories because your body has to warm it up. This is technically true, but the numbers are tiny. Drinking about two liters of water per day (roughly half a gallon) at cool temperatures increases energy expenditure by about 400 kilojoules, or roughly 95 calories. About 40% of that thermogenic effect comes specifically from warming the water to body temperature.
That means the calorie cost of warming cold water alone accounts for maybe 38 calories across an entire day’s worth of water intake. It’s real, but it’s roughly equivalent to eating two or three potato chips. Not a weight loss strategy on its own, though researchers have noted it’s worth factoring into overall energy expenditure calculations.
The Bottom Line on Temperature
For the vast majority of people, ice water is perfectly safe. It temporarily slows stomach emptying, mildly activates the vagus nerve, and can slow nasal mucus flow. None of these effects cause harm in healthy individuals. The people who benefit most from avoiding ice water are those with active migraines, achalasia or esophageal motility issues, or significant tooth sensitivity. If you’re congested, warm water is the better choice. If you’re exercising, cold water helps keep your core temperature down. Otherwise, drink whatever temperature you prefer.