Cold water will not make a typical illness worse, and staying hydrated matters far more than the temperature of what you drink. That said, warm and hot fluids do offer real, measurable advantages when you are fighting a cold or flu, particularly for clearing congested nasal passages. The choice between cold and warm water during illness is less about danger and more about which minor benefits you want to lean into while your body recovers.
Cold Water Slows Mucus Clearance, Hot Water Speeds It Up
One of the clearest findings in this area comes from a study that measured how quickly the mucus lining in your nose moves after drinking fluids at different temperatures. Your nasal mucus acts like a conveyor belt, trapping viruses and bacteria and sweeping them toward your throat to be swallowed and neutralized by stomach acid. When that conveyor belt slows down, germs linger longer in your airways.
Drinking cold water slowed nasal mucus velocity from about 7.3 to 4.5 millimeters per minute, a drop of roughly 40 percent, and that effect was still detectable 30 minutes later. Hot water and chicken soup, by contrast, sped mucus movement up, with both returning to baseline within half an hour.1PubMed. Effects of drinking hot water, cold water, and chicken soup on nasal mucus velocity and nasal airflow resistance A separate review confirmed that ingestion of hot fluids enhances nasal mucus velocity along with exercise and decongestants.2PubMed. Mucociliary transport
When you are sick with a respiratory infection, this matters. Congestion is already slowing your mucociliary clearance. Drinking cold water can compound that slowdown, while hot water or warm broth gives your body’s built-in defense system a small boost. None of this means cold water is dangerous. It means warm drinks actively help in a way cold ones do not.
Staying Hydrated Is the Real Priority
When you have a fever, your body loses fluid faster than usual through sweating and increased breathing rate. Vomiting and diarrhea accelerate that loss further. In this context, the most important thing about any drink is that you actually consume enough of it. And this is where water temperature starts to matter in a different way: people tend to drink more of some temperatures than others.
Research on athletes who had been dehydrated found that people voluntarily drank the most water when it was cool, around 16°C (about 61°F), and that both very cold water (5°C) and hot water (58°C) led to less voluntary intake.3PubMed Central. Water temperature, voluntary drinking and fluid balance in dehydrated taekwondo athletes A related study confirmed the same pattern, finding that cool water at 16°C prompted higher intake and better hydration compared to other temperatures.4PubMed Central. The effect of water temperature and voluntary drinking on the post rehydration sweating This runs counter to the popular idea that ice-cold water is the most refreshing option. In practice, moderately cool water seems to hit the sweet spot for getting people to drink voluntarily.
There is an exception during exercise in the heat, where very cold water (4°C) increased both fluid intake and endurance, likely because it functioned as a heat sink that helped lower core body temperature.5PubMed. Drink temperature influences fluid intake and endurance capacity in men during exercise in a hot, dry environment But for someone lying in bed with a fever, that athletic scenario is not really relevant. The takeaway for sick people is straightforward: if cool or room-temperature water helps you drink more, that is better than sipping a hot tea you do not finish.
What Cold Water Does to Your Stomach
If you have ever felt a bit off after chugging ice water on an empty stomach, there is a physiological reason. Cold water temporarily slows down gastric contractions. One study found that drinking water at 2°C lowered the frequency of stomach contractions compared to water at 60°C, and that slower gastric motility was associated with lower energy intake.6PubMed Central. The effects of water temperature on gastric motility and energy intake in healthy young men Cold drinks also empty from the stomach more slowly than room-temperature ones, at least initially.7PubMed Central. Effect of meal temperature on gastric emptying of liquids in man
Before you worry too much about that, consider how quickly your stomach neutralizes the temperature difference. After swallowing a cold beverage, intragastric temperature drops from about 36.5°C to 23°C but recovers to above 30°C within just five minutes.8PubMed. Gastric emptying of cold beverages in humans: effect of transportable carbohydrates Your stomach is basically a warm water bath for anything you put in it, and the thermal effect of cold liquid is small and fleeting.
Still, if you are already nauseous or have a stomach bug, this brief slowdown in gastric activity could feel uncomfortable. When your gut is irritated, adding a thermal shock on top of that irritation is not ideal. Room-temperature or warm fluids are gentler in this situation, not because cold water is harmful, but because it adds one more minor stressor your digestive system has to deal with.
Effects on Your Esophagus and Swallowing
Cold water also affects how your esophagus contracts when you swallow. In healthy people, cold water reduced the strength of esophageal contractions compared to room-temperature water, with the contractile force dropping to roughly two-thirds of what it was at room temperature during normal swallows.9PubMed Central. Effect of Cold Water on Esophageal Motility in Patients With Achalasia and Non-obstructive Dysphagia: A High-resolution Manometry Study Cold water also slows the speed at which the swallowing wave travels down the esophagus and prolongs the duration of each contraction.10PubMed. The effect of water bolus temperature on esophageal motor function as measured by high-resolution manometry
For most healthy people, this is imperceptible. But if you already have swallowing difficulties or a condition like achalasia, cold water can make things worse. Iced water increased resting pressure at the lower esophageal sphincter and prolonged contraction duration in patients with achalasia, while hot water had the opposite, relaxing effect.11Journal of Neurogastroenterology and Motility. Response of Esophagus to High and Low Temperatures in Patients With Achalasia If you are sick and already have a sore, inflamed throat, the brief tightening effect of cold water on esophageal muscles may make swallowing feel harder, even though it is not causing any actual damage.
Cold Water, Your Heart Rate, and the Vagus Nerve
Drinking ice water triggers a noticeable response in your autonomic nervous system, the part of your nervous system that controls unconscious functions like heart rate and digestion. A study in young women found that both branches of the autonomic nervous system activated after cold water ingestion: sympathetic activity (the “fight or flight” system) increased immediately, while parasympathetic activity (the “rest and digest” system) ramped up within ten minutes.12PubMed Central. The effect of cold water intake on heart rate variability in young women: the co-activation of the sympathetic and parasympathetic branches of the autonomic nervous system
The net result is typically a brief slowing of the heart rate. Another study confirmed this, showing that ice water increased vagal (parasympathetic) activity and decreased heart rate compared to room-temperature water.13PubMed. The effect of ice water ingestion on autonomic modulation in healthy subjects For a healthy person, this is harmless and temporary. But when you are already sick, your heart rate and autonomic balance may be altered by fever or medications. The added vagal stimulation from ice water is unlikely to cause a problem, but it is worth knowing about if you feel lightheaded or dizzy after drinking very cold water while ill.
Cold Water Headaches and Migraine Triggers
“Brain freeze” is not just a slushie problem. In a study of 669 women, about 8 percent developed a headache after drinking just 150 milliliters of ice-cold water through a straw. Women who had experienced a migraine in the past year were twice as likely to get a headache from the cold water as women who had never had migraines. Interestingly, women whose migraines had been inactive for more than a year were not at increased risk.14PubMed. Headache caused by drinking cold water is common and related to active migraine
If you are already dealing with a sinus headache or a migraine triggered by illness, ice-cold water could pile on. This does not mean cold water causes lasting harm, but it is a real, reproducible discomfort that some people are genuinely susceptible to. Opting for room-temperature or warm water eliminates this trigger entirely.
Asthma and Respiratory Sensitivity
For people with asthma, cold water deserves extra caution. A study of asthmatic children found that nearly half (47 percent) of children in the asthma group developed coughing or wheezing after drinking ice water, compared to just 4 percent of non-asthmatic children.15PubMed. Asthma induced by ice water ingestion in ethnic Chinese asthmatic children: a challenge The cold stimulus appeared to trigger airway narrowing in susceptible children.
If you or your child has asthma and is also fighting a respiratory illness, ice-cold drinks could worsen breathing symptoms at exactly the wrong time. This is one situation where the temperature of your fluids genuinely matters beyond comfort. Room-temperature or warm fluids avoid the airway-constricting reflex altogether.
Why Hot Drinks Help With Medication Absorption
If you are taking acetaminophen (paracetamol) to manage fever or aches, the way you take it can affect how fast it works. A study comparing paracetamol dissolved in a hot drink versus a standard tablet found that the hot drink reached a therapeutic concentration in about 5 minutes versus 23 minutes for the tablet. The hot drink also triggered faster gastric emptying, moving from the stomach into the intestine where absorption happens in about 8 minutes compared to 54 minutes for the tablet.16PubMed Central. Does a Hot Drink Provide Faster Absorption of Paracetamol Than a Tablet? A Pharmacoscintigraphic Study in Healthy Male Volunteers
The peak blood concentration was actually slightly higher with the tablet (since the dissolved form spread its absorption over a longer stretch of intestine), but the speed advantage of the hot drink is significant when you are waiting miserably for a fever reducer to kick in. If you normally chase your paracetamol tablet with cold water, know that the cold water’s brief gastric-slowing effect is working in the opposite direction from what you want.
The Persistent Myth That Cold Water Causes Illness
In many cultures, drinking cold water, particularly when sweating or already feeling unwell, is believed to directly cause colds and other illnesses. A survey on common cold misconceptions found a statistically significant gender difference in the belief that “drinking cold water when sweaty causes common cold,” with the belief being widely held overall.17DergiPark. Traditional patient misconceptions about the causes and care of the common cold This belief persists in parts of Asia, Latin America, the Middle East, and elsewhere, sometimes strongly enough that patients avoid cold fluids entirely when sick.
The common cold is caused by viruses, not by temperature exposure. Cold water does not suppress your immune system or invite pathogens in. What the evidence does show, as described throughout this article, is that cold water can temporarily slow mucus clearance, affect gut motility, and trigger discomfort in susceptible people. These are real but minor physiological effects. Confusing them with causing disease leads to people avoiding hydration when they need it most, which is the actual risk.
Fever Management and Fluid Temperature
You might assume that drinking ice water when feverish would help cool you down faster. The reality is more nuanced. A review of external cooling methods for fever found that physical cooling methods are the treatment of choice for true hyperthermia (like heat stroke), but their value in treating fever from infection remains uncertain. Fever is a regulated elevation in your body’s temperature set point, so your body actively works to maintain that higher temperature. Methods involving evaporation and convection (like tepid sponging) are somewhat effective, but are generally uncomfortable, and in children, tepid sponging combined with fever-reducing medication did not offer enough benefit over medication alone to justify the added discomfort.18Oxford Academic (Clinical Infectious Diseases). External Cooling in the Management of Fever
Drinking cold water during a fever works on the same principle as external cooling by conduction: you are putting something cold inside yourself hoping to bring the temperature down. But since your hypothalamus has deliberately raised the set point, your body will generate more heat to compensate. The cold water gets warmed in your stomach within minutes. At best, you get a brief, marginal temperature dip. At worst, you trigger shivering, which actually generates more heat. The better strategy is to take appropriate antipyretic medication, stay hydrated with whatever temperature you will actually drink, and let the medication do the real work of resetting your thermostat.
Practical Guidance for Different Scenarios
Not every illness is the same, and the “best” water temperature depends on what you are dealing with. Here is a quick breakdown:
- Nasal congestion: Warm or hot fluids have a clear advantage, actively speeding up mucus clearance. Soups, hot tea, and warm water all help. Cold water works against you here.
- Fever with dehydration: Drink whatever temperature you will actually finish. Cool water around 16°C tends to encourage the highest voluntary intake. Avoid very hot drinks if they make you sweat more.
- Sore throat: This is genuinely a matter of personal preference. Some people find cold water soothing because it numbs irritated tissue. Others prefer warm water with honey. Neither is medically superior for the infection itself.
- Stomach bug: Room-temperature or slightly warm fluids are gentler. Cold water briefly slows gastric motility and could add discomfort when your gut is already irritated.
- Asthma plus a respiratory infection: Avoid ice-cold drinks. The cold stimulus can trigger airway narrowing on top of infection-related inflammation.
- Migraine-prone and sick: Skip ice water. Room temperature or warm avoids the cold-triggered headache that migraine sufferers are more susceptible to.
Cooling Methods That Do Help Your Immune System
While cold water drinking does not boost your immune function in any meaningful way, there is an interesting wrinkle from research on body cooling more broadly. A study on workers in hot environments found that local cooling methods significantly increased salivary IgA concentrations, an antibody that plays a key role in mucosal immunity. Workers using cooling garments had salivary IgA levels roughly 132 percent higher than those without any cooling, and even a simple face-cooling setup raised levels by about 76 percent.19Results in Engineering. Comparing the improve effect of local cooling on worker’ thermal comfort, EEG, and salivary IgA concentration in hot environments
The mechanism here is not about drinking cold water; it is about relieving heat stress. When your body is overheated, the physiological strain diverts resources away from immune surveillance. Bringing core or surface temperature back toward a comfortable range lets the immune system function better. If you have a fever and are lying under heavy blankets in a warm room, removing a layer or turning a fan on may do more for your immune system than drinking ice water, which mainly just cools the inside of your stomach for a few minutes before being thermally neutralized. The lesson from this research is that comfortable is better than extreme in either direction. Your immune system works best when your body is not under thermal stress, whether that stress comes from overheating or from aggressive chilling.