13 Dehydration Symptoms Everyone Should Know, According to Experts

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 water. 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, told Health. Here's what to know about common dehydration symptoms, including feeling thirsty and passing out—and all the signs in between.

Bad Breath

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, told Health. "Saliva has important antibacterial properties," Young said. "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.

Sugar Cravings

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, told 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.

Dry Skin

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, told 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 the back of your hand; if the skin doesn't bounce back right away, it's begging you for water. For smooth, moisture-rich skin, Dr. Tremaine also suggested keeping showers short (less than five minutes) and using only lukewarm water, as hot water can dry your skin out even more.

Tiredness

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, told Health. Physical tasks may also feel more difficult and tiring because your muscles are lacking H2O, which is necessary for them to function properly.

Irritability

If you're feeling cranky, drink a glass of water and your mood may change. "Neurological effects of dehydration can cause irritability," Dr. Podesta said. A 2014 study, published in PLoS ONE, of 52 adults examined the effects of hydration on mood. Those who habitually had low water intake showed an improvement in mood, particularly at sleep and wake times, when water intake was increased. On the other hand, those whose water intake was high reported negative effects on mood when water intake was reduced; this effect was most noticeable on calmness, satisfaction, and positivity, as well as at sleep and wake times.

Chills

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 said. In addition, water holds heat, so if you become dehydrated 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.

Muscle Cramps

When your body isn't getting enough water, it slows down blood circulation, which can make your muscles cramp, Ray Casciari, MD, a pulmonologist in Orange, California, told Health. "The body will protect its vital organs, so it shifts fluid away from muscles and anything that's not vital," Dr. Casciari said. 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.

Lightheadedness and Confusion

Along with your muscles, your brain also gets less blood circulation when you're low on water, which can make you dizzy, Dr. Casciari said—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 explained. "We would give them a liter over an hour via an IV," Dr. Sutton-Oliver said.

Headache

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 said. 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 suggested.

Constipation

According to the National Institute of Diabetes and Digestive and Kidney Diseases, 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.

Dark-Colored Urine

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 said. When you're dehydrated, your kidneys, which filter waste, tell your body to retain water. This 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.

Excessive Thirst

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

Low Blood Pressure

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 told Health. However, low blood pressure can manifest in a few different ways, including nausea, dizziness, and blurred vision, so it's important to be aware of these symptoms, 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 added. 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," Dr. Goldberg explained.