13 Dehydration Symptoms Everyone Should Know, According to Experts

Dehydration does more than just make you thirsty—it can actually be quite dangerous to your health. Here's how to know when your body is telling you to drink more water, so that you don't let it get to the later stages of dehydration.

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In general, dehydration occurs when your body loses too much fluid, or more fluid than it's taking in, according to the US National Library of Medicine's resource MedlinePlus.

You can become dehydrated for a number of reasons, but the main culprits include: diarrhea, vomiting, sweating too much, urinating too much, having a fever, or (simply) not drinking enough. And it doesn't take much to become dehydrated: if you lose just 1.5% of the water in your body, you've reached the tipping point of dehydration.

While dehydration often shows up as the standard thirsty feeling, the later stages of the condition can actually lead to a loss of consciousness, Jazmine Sutton-Oliver, MD, who works in hospital medicine at the Cleveland Clinic, tells Health. Here's what to know about common dehydration symptoms, including feeling thirsty and passing out—and all the signs in between.

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Bad Breath

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Notice your breath smelling the opposite of minty fresh? It could be because you haven't drank enough water lately, Marshall Young, DDS, a dentist in Newport Beach, California, tells Health. "Saliva has important antibacterial properties," he says. "When dehydrated, the decreased saliva in the mouth allows bacteria to thrive, resulting in bad breath."

Also, while we're talking about your mouth, dehydration can cause it to feel dry, for obvious reasons. So drink up for your own sake—and for the people around you, too.

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Sugar Cravings

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Dehydration can mask itself as hunger, or more specifically as sugar cravings. This is more likely to happen if you've been exercising, Amy Goodson, RD, a sports dietitian, tells Health. "When you exercise in a dehydrated state, you use glycogen, or stored carbohydrates, at a faster rate, thus diminishing your stores more quickly." So once you finish exercising, you will likely crave carbs (aka sugar) to help you replenish those glycogen levels. Pro tip: Before reaching for a chocolate bar, drink a tall glass of water and wait five minutes. You might not be as hungry as you think. (After that, if you're still craving something sweet, go ahead and have it.)

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Dry Skin

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Your skin will let you know if you haven't been drinking enough water, Anne Marie Tremaine, MD, a dermatologist at Skin Wellness Physicians in Naples and Marco Island, Florida, tells Health. Dehydrated skin will feel tight and appear dull when you look in the mirror. You may even notice more exaggerated wrinkles or darker-than-usual under eye circles.

A quick test if you're feeling less than hydrated: Pinch your cheeck; if it wrinkles with gentle pressure instead of holding its shape, it's begging you for water. For smooth, moisture-rich skin, Dr. Tremaine also suggests keeping showers short (less than five minutes) and using only lukewarm water, as hot water can dry your skin out even more.

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That mid-afternoon slump may have more to do with dehydration than you think. A number of the symptoms of dehydration can make you feel sleepy, Luga Podesta, MD, a sports medicine specialist at Bluetail Medical Group in Naples, Florida, tells Health. Physical tasks may also feel more difficult and tiring because your muscles are lacking H2O, which is necessary for them to function properly.

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If you're feeling cranky, drink a glass of water and your mood may change. "Neurological effects of dehydration can cause irritability," Dr. Podesta says. A small 2011 study published in the Journal of Nutrition tested mood and concentration in 25 young women who were either given enough fluids to remain properly hydrated, or who became mildly dehydrated by taking diuretics and exercising. The dehydrated women—who were at a hydration level that was just 1% lower than optimal—reported headaches, loss of focus, and irritability.

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It may seem counterintuitive, but dehydration can bring on chills. "This occurs because your body starts to limit blood flow to the skin," Dr. Podesta says. In addition, water holds heat, so if you become hydrated it can be more difficult to regulate your body temperature, which can make you get chilly faster, even when you're not in a cold environment.

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Muscle cramps

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When your body isn't getting enough water, it slows down blood circulation, which can make your muscles cramp up, Ray Casciari, MD, a pulmonologist in Orange, California, tells Health. "The body will protect its vital organs, so it shifts fluid away from muscles and anything that's not vital," he says. Changes in sodium and potassium through sweat loss can also contribute to cramping. Cramps can be extremely painful and make muscles feel harder to the touch.

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Lightheadedness and confusion

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Along with your muscles, your brain also gets less blood circulation when you're low on water, which can make you dizzy, Dr. Casciari says—and this can constitute a situation when dehydration can warrant medical attention.

When a person becomes so dehydrated that they're taken to the emergency room, doctors usually try to get water back into their body very quickly, Dr. Sutton-Oliver explains. "We would give them a liter over an hour" via an IV, she says.

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Dehydration can cause headaches in a couple of different ways. "Lack of water affects your body's serotonin levels, which can give you headaches," Dr. Casciari says. In addition, small blood vessels in the brain respond quickly to hydration levels (which is also the culprit behind those nasty hangover headaches), leading to dull aches and even full-blown migraines.

Try downing a glass or two of water the next time you have a headache and you may find it disappears. You could also eat fruit, which contains a lot of water, Dr. Casciari suggests.

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Your body needs water to keep things moving through your colon. When you're not getting enough H2O, your body compensates by withdrawing more fluid from stool, making it harder and more difficult to pass. That said, it's worth noting that drinking more water when you're already properly hydrated won't necessarily relieve constipation caused by other factors, like the medications you're taking, medical conditions, or a lack of fiber in your diet.

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Dark-colored urine

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One telltale sign of dehydration is dark yellow urine. "A lot of people will notice their urine starts to get concentrated or dark in color," Dr. Sutton-Oliver says. When you're dehydrated, your kidneys, which filter waste, tell your body to retain water. That means you'll have less water in your urine, causing it to become more concentrated with waste products and, therefore, darker. If you notice your urine is darker than usual, reach for your water bottle.

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Excessive Thirst

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It might seem obvious, but being thirsty is a big hint that you're not as hydrated as you should be, Dr. Sutton-Oliver says. When you get dehydrated, you'll naturally be thirsty, so listen to your body's signals and rehydrate until you've quenched your thirst.

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Low Blood Pressure

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While not drinking enough water can cause a plethora of symptoms, one in particular, low blood pressure, can be especially dangerous, Eric Goldberg, MD, an internal medicine physician at NYU Langone tells Health. But low blood pressure can manifest in a few different ways, including nausea, dizziness, and blurred vision, so it's important to be aware of those, as many of us don't have blood pressure cuffs at home.

Low blood pressure can be especially dangerous, as it means your blood isn't getting properly sent to critical organs, including your brain, Dr. Goldberg adds. Certain blood pressure medications act as diuretics, which make the body urinate fluid out of it much faster. People who take these medications are more susceptible to becoming dehydrated, per Dr. Goldberg. The good news? "Most people can fix that simply by drinking water," he explains.

Updated by
Maggie O'Neill
Maggie O’Neill

Maggie O’Neill is a health writer and reporter based in New York who specializes in covering medical research and emerging wellness trends, with a focus on cancer and addiction. Prior to her time at Health, her work appeared in the Observer, Good Housekeeping, CNN, and Vice. She was a fellow of the Association of Health Care Journalists’ 2020 class on Women’s Health Journalism and 2021 class on Cancer Reporting. In her spare time, she likes meditating, watching TikToks, and playing fetch with her dog, Finnegan.

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