How to Tell If You Are Dehydrated, According to Doctors

It’s no secret that water bottle culture is big in the US — so much so, that it might come as a surprise to hear that dehydration is super common. If Stanleys and Owalas are as popular as they seem on TikTok, isn’t everyone chugging water all day long? And yet, dehydration is rampant (although medical information publisher StatPearls notes that the 75 percent figure you often see cited may be a little overblown). But how can you tell if you’re dehydrated?

One easy way: are you thirsty? That’s an early sign of dehydration, says Natasha Bhuyan, MD, a primary care provider with One Medical and an assistant clinical professor of Family Community & Preventive Medicine at the University of Arizona. But there are other, less-obvious symptoms too. Here, exactly how to tell if you’re dehydrated, according to two MDs.

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Natasha Bhuyan, MD, is a primary care provider with One Medical and an assistant clinical professor of Family Community & Preventive Medicine at the University of Arizona.

Paul Fenyves, MD, is an internist at Weill Cornell Medicine and NewYork-Presbyterian.

What Is Dehydration?

Dehydration occurs when you don’t have enough water in your body, or when you lose too much without replenishing it fast enough. “Your body attempts to conserve water however it can, whether by thickening your blood, preventing you from urinating, or pulling fluid from other places like tissue,” Dr. Bhuyan tells PS. Rapid fluid loss can result from diarrhea, vomiting, or sweating. Prescription medications that are classified as diuretics and cause increased urination, laxatives, as well as certain foods and drinks like alcohol, can also be culprits of dehydration, she said. She named HCTZ, a blood pressure medication, as an example of a diuretic.

Paul Fenyves, MD, internist at Weill Cornell Medicine and NewYork-Presbyterian, says that dehydration can also occur when your body doesn’t have enough salt. “We need salt to hold on to our fluids,” he says. That’s why if people sweat a lot, losing fluids and salt, and they just drink water, the lack of sodium could still cause dehydration.

Symptoms of Dehydration

Early signs of dehydration are increased thirst, less frequent urination, darker urine, and dry lips, mouth, and skin, Dr. Bhuyan says. Once dehydration becomes more severe, people may have difficulty making tears, feel dizzy, or get a headache. “If someone has severe dehydration, their heart rate increases, they may feel confused or get a fever, they will move slower than usual and have trouble walking, and they may have a drop in blood pressure or even pass out,” she explains.

Lightheadedness upon standing due to a drop in blood pressure, called orthostatic hypotension, can occur, and tiredness or weakness are other typical signs, Dr. Fenyves adds, noting that the symptoms are pretty general and might not show up at first. Fatigue, for example, could happen because of dehydration, a virus, or another reason. “It’s all a bunch of nonspecific symptoms,” he says.

But if you feel any of them significantly, see a doctor. In terms of treatment, Dr. Bhuyan says she would give a patient oral or IV fluids, then treat any underlying causes, such as constipation and kidney stones, both of which can cause chronic, mild dehydration. In addition, increased thirst and urination can indicate underlying diabetes, Dr. Fenyves says.

He advises that if you’re thirsty more than you think you should be, getting medical attention is a good idea. Diabetics and people with heart disease as well as older adults should be particularly wary of dehydration because their bodies aren’t as resilient, he notes. Severe dehydration can also turn deadly if left untreated.

Symptoms of Dehydration in Elderly

Older adults become dehydrated more easily than others. Hot and humid weather is a risky time, as is sick season — influenza, bronchitis, and bladder infections can sap fluid reserves more quickly than normal, reports the Mayo Clinic. And this group may only feel thirsty once they’re already truly dehydrated, so it’s important to be aware of the other signs: infrequent and/or dark-colored urination, fatigue, confusion, and dizziness.

A Note About Heatstroke

Working out in excessive heat can cause dehydration since you’re sweating profusely, but Dr. Fenyves says a lot of people that get sick from being in high temperatures experience heatstroke. “In order to maintain what’s called homeostasis, for all of the different chemical reactions in your body to work, your body has to be in this small temperature range,” he explains. Your body overheats, especially when it’s humid, and your core temperature can rise to 104 or higher, he said.

You can certainly both be dehydrated and experience heatstroke in the heat, but the difference between the two is that while dehydration can be caused by sweating in the heat and therefore loss of fluids and salt, it can also be caused by other factors, such as diarrhea and vomiting. Heatstroke is only caused by hot temperatures, and it can occur even if you’re hydrated, Dr. Fenyves says. He used the following example: You wouldn’t be able to go to Mars, where it’s hundreds of degrees, and avoid heatstroke by drinking fluids.

How to Avoid Dehydration

Dr. Bhuyan says that the “eight by eight” rule is a popular recommendation. This means drinking eight ounces of water about eight times per day. But this doesn’t apply to everyone, and the the amount of water you should be drinking each day depends on your weight and health status. Dr. Fenyves stresses that he doesn’t think you need to constantly worry about drinking water. “It’s definitely not a rule that every time you pee it should look like a clear mountain stream,” he tells PS. “Your body can tell you when you need fluid by making you thirsty.” Dr. Bhuyan, though, encourages her clients to stay hydrated even when they’re not thirsty.

Other tips from these doctors for avoiding dehydration, especially in the warmer months, include:

Samantha Brodsky is a former assistant editor at POPSUGAR. She uses her gymnast background to inform her sports and fitness coverage, powering through Peloton videos in her free time.