COVID-19 can absolutely dehydrate you, and it often does so through several routes at once. Fever burns through fluids, the virus can infect gut cells and trigger diarrhea, your lungs lose extra moisture during labored breathing, and the illness itself can kill your appetite and thirst drive. In one study of long-term care residents hospitalized with COVID, roughly six in ten met laboratory criteria for dehydration. The mechanisms behind this fluid loss are more varied than most people realize, and some of them continue to matter even after the acute infection clears.
How Common Is Dehydration in COVID Patients
The rates depend on the population studied and how dehydration is measured, but the numbers are consistently high. A study of 261 long-term care residents with COVID-19 found that 59% were dehydrated based on blood markers, and among those with elevated sodium levels, the average free-water deficit was nearly three liters.1PubMed Central. Co-Occurring Dehydration and Cognitive Impairment During COVID-19 in Long-Term Care Patients A separate study of hospitalized COVID patients found that about a quarter had a measurable fluid deficit on admission.2The Egyptian Journal of Internal Medicine. Investigating the relationship of hydration status on the clinical outcomes of COVID-19 patients These figures likely undercount mildly dehydrated people who never got blood work, since most cases of COVID are managed at home without lab tests. The takeaway is that dehydration during COVID is not an occasional side effect. It is one of the most common complications of the infection.
Why the Virus Drives Fluid Loss
Several mechanisms work in parallel to drain your body of water during a COVID infection. Understanding which ones are hitting you can help you respond more effectively.
Fever and Increased Metabolic Demand
Fever is the most obvious culprit. When your body temperature rises, you sweat more and breathe faster, both of which pull water out of your system. For every degree of temperature elevation, your body’s baseline water needs go up. COVID fevers can persist for days, and many people underestimate how much extra fluid this requires because they do not feel thirsty enough to keep pace with the loss. The combination of fever, rapid breathing, and reduced appetite creates a gap between what your body is losing and what you are taking in.
Diarrhea and Gut Infection
COVID is not just a respiratory illness. SARS-CoV-2 uses the ACE2 receptor to enter cells, and those receptors are abundant in the lining of your intestines. Research has confirmed that the virus directly enters and replicates inside gut cells called enterocytes.3Cellular and Molecular Gastroenterology and Hepatology. COVID-19 Diarrhea Is Inflammatory, Caused by Direct Viral Effects Plus Major Role of Virus-induced Cytokines This leads to inflammation and increased permeability of the gut lining, which can cause diarrhea. Several contributing factors pile on: the virus disrupts the normal gut microbiome, antiviral medications and antibiotics used during treatment have their own gastrointestinal side effects, and the inflammatory response itself makes the gut leak more fluid than normal.4PubMed Central. COVID-19 and diarrhea: putative mechanisms and management Diarrhea does not just remove water. It washes out electrolytes like sodium, potassium, and chloride, which makes the fluid imbalance harder to fix with water alone.
Respiratory Water Loss
Every breath you take humidifies the air before it reaches your lungs, and that moisture has to come from somewhere. Under normal conditions, your lungs account for roughly a quarter of total daily water loss. When you are sick with COVID and breathing harder or faster than usual, that percentage climbs. Labored breathing, coughing fits, and mouth breathing all increase the rate at which you exhale moisture. In people who develop more severe respiratory illness, the losses can become substantial enough to thin the mucus lining of the upper airways, which ironically can make the infection worse by reducing the effectiveness of the cilia that help clear pathogens.5Nature (Scientific Reports). COVID-19 symptoms are reduced by targeted hydration of the nose, larynx and trachea
When You Stop Wanting to Drink
Beyond the direct physical mechanisms, COVID also sabotages the behavioral side of staying hydrated. Loss of taste and smell is one of the infection’s signature symptoms, and it has a surprising downstream effect on fluid intake. When everything tastes bland or like nothing at all, people lose interest in eating and drinking.6PubMed Central. Varied Effects of COVID-19 Chemosensory Loss and Distortion on Appetite: Implications for Understanding Motives for Eating and Drinking Water already has minimal flavor, and when you add nausea, fatigue, and a general feeling of being too miserable to get out of bed, hydration drops down the priority list. This is especially true for people living alone or managing their illness at home, where no one is reminding them to take sips regularly. The illness-induced apathy toward fluids is easy to underestimate and probably accounts for a large share of dehydration in mild-to-moderate cases that never involve diarrhea or high fevers.
How the Virus Disrupts Fluid Regulation at a Deeper Level
The ACE2 receptor that SARS-CoV-2 uses to enter cells is not just a doorknob for the virus. It is part of a system your body uses to regulate blood pressure and fluid balance. When the virus binds to and downregulates ACE2, it throws off this regulatory system.7PubMed Central. The fight against COVID-19: Striking a balance in the renin-angiotensin system The downstream effects can include shifts in how your kidneys handle sodium and water, contributing to the electrolyte disturbances that frequently show up in COVID patients. This means dehydration during COVID is not only about losing fluid through sweat, stool, and breath. The virus also interferes with your body’s ability to manage the fluid it still has.
Electrolyte Imbalances That Accompany the Fluid Loss
Dehydration during COVID is not just about water volume. It often comes with clinically meaningful shifts in electrolyte levels. A case-control study of over a thousand emergency department patients found that COVID-positive patients were significantly more likely to have low sodium, low potassium, and low chloride levels compared to patients without COVID. About one in five COVID patients had low sodium, and roughly one in seven had low potassium. After adjusting for other factors, the odds of low sodium were nearly doubled in COVID patients, and low potassium was similarly elevated.8PubMed Central. Electrolyte imbalance in COVID-19 patients admitted to the Emergency Department: a case–control study These electrolyte shifts matter because they can cause muscle cramps, heart rhythm disturbances, confusion, and weakness on top of an already brutal illness. They also mean that rehydrating with plain water alone may not fully correct the problem.
Who Faces the Highest Risk
Older adults are especially vulnerable. They start with a lower baseline of total body water, their thirst sensation is blunted with age, and many take medications like diuretics that increase fluid loss. Dehydration in older people is independently associated with longer hospital stays, higher rates of intensive care admission, and worse overall outcomes.9PubMed Central. Hydration Status in Older Adults: Current Knowledge and Future Challenges Add COVID on top of those baseline risks, and you get the kind of numbers seen in the long-term care study mentioned earlier, where most residents ended up dehydrated.
Young children are another high-risk group because they have a higher surface-area-to-weight ratio and lose fluid proportionally faster, though they also tend to recover faster when rehydrated. People with diabetes face a particular compound risk: dehydration from COVID can worsen blood sugar control, and there is some evidence that SARS-CoV-2 may directly damage insulin-producing cells in the pancreas, potentially triggering diabetic ketoacidosis, a dangerous condition where severe dehydration and acidic blood levels spiral together.10Acute and Critical Care. Impact of the COVID-19 pandemic on diabetic ketoacidosis management in the pediatric intensive care unit Anyone with chronic kidney disease, heart failure, or conditions requiring fluid-sensitive medications should be especially watchful.
How Dehydration Makes COVID Complications Worse
Dehydration does not just make you feel lousy. It creates a cascade of secondary risks that can turn a manageable COVID case into a more serious one. The most direct risk is kidney injury. When the body is low on fluid, blood flow to the kidneys drops, creating what clinicians call a prerenal state. In a study of COVID patients who developed acute kidney injury, the majority of cases had this prerenal cause.11PubMed Central. Acute kidney failure in patients admitted due to COVID-19 In other words, the kidneys were failing not because they were directly damaged but because they were not getting enough blood flow, largely due to dehydration.
This is where over-the-counter pain medications enter the picture. Many people reach for ibuprofen or other anti-inflammatory drugs to manage COVID fevers and body aches. These medications reduce blood flow to the kidneys by constricting certain blood vessels in the filtering units. In a well-hydrated person, that effect is minor. But in someone already dehydrated from a viral infection, the combination of low fluid volume and reduced kidney blood flow creates a synergistic risk for acute kidney injury.12PubMed Central. NSAIDs may increase the risk of thrombosis and acute renal failure in patients with COVID-19 infection Acetaminophen (Tylenol) is generally considered a safer choice for fever management during COVID for this reason, though anyone with liver issues should check with their doctor on dosing.
Dehydration also thickens the blood by reducing plasma volume. COVID already raises the risk of blood clots on its own, and patients with clotting complications face a higher risk of death.13PubMed Central. Risk of Thrombosis during and after a SARS-CoV-2 Infection: Pathogenesis, Diagnostic Approach, and Management Adding dehydration to an already pro-clotting environment is a combination worth taking seriously, especially for people who are bed-bound with severe symptoms and not moving around much.
Practical Ways to Stay Hydrated During COVID
If you are managing COVID at home, the goal is to replace fluid steadily rather than playing catch-up once you feel parched. Thirst is not a reliable signal during acute illness, particularly for older adults. Here are approaches that actually help:
- Sip regularly: Small, frequent sips are easier on a nauseous stomach than large gulps. Set a timer on your phone if you tend to lose track.
- Use electrolyte drinks: Because COVID often depletes sodium and potassium along with water, drinks containing electrolytes and some sugar are more effective for rehydration than plain water. Research on rehydration solutions shows that beverages with a moderate carbohydrate-electrolyte concentration outperform plain water for restoring fluid balance.14PubMed Central. Oral Rehydration Beverages for Treating Exercise-Associated Dehydration: A Systematic Review, Part I. Carbohydrate-Electrolyte Solutions Commercial oral rehydration solutions, sports drinks, or even diluted fruit juice with a pinch of salt can work. Full-strength sodas or energy drinks are poor choices because their high sugar content can worsen diarrhea.
- Eat watery foods: If you can tolerate solid food, broths, soups, watermelon, ice pops, and yogurt all contribute to your fluid intake. Broth is particularly useful because it supplies sodium.
- Avoid alcohol and excess caffeine: Both have mild diuretic effects that you do not need when you are already behind on fluids.
- Monitor urine color: Pale yellow is the general target. Dark amber suggests you need more fluid. This is a rough guide and not perfectly accurate in older adults, but it is the most practical home test available.
For people with heart failure or kidney disease, the advice gets more nuanced. Aggressive fluid intake can backfire by worsening fluid overload in the lungs. Hospitalized COVID patients with severe respiratory distress actually tend to do worse with large amounts of intravenous fluid, as higher fluid accumulation in the lungs is linked to longer time on a ventilator.15Rational Use of Intravenous Fluids in Critically Ill Patients. Fluid Management in COVID-19 If you have a condition that requires fluid restriction, talk to your care team about how to balance hydration against overload during a COVID infection rather than just drinking as much as possible.
Recognizing Dehydration When Classic Signs Fail
Most people know the standard checklist: dry mouth, dark urine, skin that tents when you pinch it. The problem is that these signs are unreliable, especially in older adults. A systematic review of physical markers for dehydration in elderly patients found that all of the classic physical signs had poor sensitivity, meaning they frequently miss dehydration that is actually present. Urine color and urine concentration tests were not much better, performing barely above chance at distinguishing hydrated from dehydrated individuals.16PubMed. Is this elderly patient dehydrated? Diagnostic accuracy of hydration assessment using physical signs, urine, and saliva markers This means you cannot rely on “I don’t look dehydrated” as a reason not to drink. The better approach during illness is to treat hydration proactively: assume you are losing more than you think and drink on a schedule rather than waiting for warning signs.
Warning signs that should prompt medical attention rather than more home fluids include dizziness when standing, a heart rate that stays elevated, very little or no urine output over several hours, confusion, or a dry mouth and eyes so severe that you cannot produce tears. In children, watch for an absence of tears when crying, fewer wet diapers, and unusual listlessness.
Dehydration and Long COVID
The fluid story does not necessarily end when the acute infection clears. One of the more common features of long COVID is a condition called postural orthostatic tachycardia syndrome, or POTS, where your heart rate spikes abnormally when you stand up. A key feature seen in most people with POTS is reduced blood volume, which lowers the amount of blood returning to the heart and triggers a compensatory increase in heart rate.17PubMed Central. COVID-19 Induced Postural Orthostatic Tachycardia Syndrome (POTS): A Review Other long COVID symptoms like internal tremor sensations may also be linked to low blood volume and the autonomic nervous system dysfunction that follows it.18PubMed Central. Internal Tremor in Long COVID May Be a Symptom of Dysautonomia and Small Fiber Neuropathy
For people dealing with post-COVID POTS, hydration becomes a long-term management tool rather than a short-term recovery measure. Many POTS specialists recommend increased daily fluid intake combined with extra salt to help expand blood volume. Compression garments and gradual exercise programs are part of the picture too, but adequate hydration is typically the foundation. If you recovered from COVID weeks or months ago but still feel lightheaded when you stand, notice your heart racing with simple position changes, or experience unexplained fatigue, it is worth discussing hydration status and POTS screening with a doctor rather than assuming you are just slow to recover.
Why NSAIDs Deserve Special Caution
The interaction between dehydration and anti-inflammatory painkillers deserves its own emphasis because it is a scenario that plays out constantly during home-managed COVID cases. You feel terrible, you take ibuprofen or naproxen for the headache and fever, and you do not realize you are already running a fluid deficit. The anti-inflammatory drug reduces blood flow to the kidneys at the same moment your kidneys are already under stress from low fluid volume.12PubMed Central. NSAIDs may increase the risk of thrombosis and acute renal failure in patients with COVID-19 infection This does not mean ibuprofen is dangerous for everyone with COVID. It means that if you choose to use it, you should be especially deliberate about hydration. If you are having diarrhea, vomiting, or barely drinking, switch to acetaminophen until your fluid intake is back to normal. People with pre-existing kidney issues should be particularly cautious and may want to avoid NSAIDs entirely during acute illness.