But dehydration is thoroughly preventable. Read on to find out what is actually happening to your body when you’re dehydrated, what to do about it, and how to help prevent it.

Signs and Symptoms of Dehydration
According to Alp Arkun, MD, chief of service for emergency at the Kaiser Permanente Fontana and Ontario Medical Centers in Southern California, fatigue, dizziness, and headaches are the top three symptoms he sees in people who show up in the emergency room when dehydration is beginning to set in. Other symptoms that come with dehydration include: (2,3)

Signs of Dehydration in Adults
Feeling thirsty
Muscle cramps
Urinating less often than normal
Dark-colored urine
Dry skin
Feeling tired or lethargic
Fainting
Confusion
Signs of Dehydration in Children
Children “are going to be much quicker to dehydrate than adults,” says Arielle Levitan, MD, an internal doctor at NorthShore Medical Group in Highland Park, Illinois. That’s because water makes up a higher proportion of total body weight for children compared to adults, making children more susceptible to the effects of not getting enough water. (4)

Sudden lethargy and weakness are possible signs of dehydration in youngsters. “Other clues can be decreased urination,” says Dr. Levitan. “You can always check their hydration by pinching their skin. If it doesn’t go back to its normal place quickly — if it is what we call ‘tented’ — that’s a pretty good sign that someone is dehydrated.” It’s important to note that skin tenting alone is an unreliable measure for dehydration, however, past research notes.

Other signs that an infant or small child is dehydrated include: (3)

Dry mouth
Crying without tears
Dry diaper after more than three hours
Sunken eyes and cheeks
A sunken soft spot on top of skull
Irritability
Learn More About Signs and Symptoms of Dehydration

The 3 Stages of Dehydration
If you go beyond 3 to 4 percent of lost fluid volume, then you are getting into the stages of dehydration, which are classified as mild, moderate, or severe. (5)

Mild (5 to 6 percent of body fluid lost) “That is usually when you start to get symptoms that you can’t dodge,” says Dr. Arkun. “You start to get fatigue, dizziness, and headaches. You slow down.”

Moderate (7 to 10 percent) At this stage symptoms can include low blood pressure, dry skin, faster-than-normal pulse, reduced urine output and skin that tents when you pinch it instead of springing back.

Severe (over 10 percent) “If you get over 10 percent, then you can get yourself into trouble,” says Arkun. “You can pass out. Because of some electrolyte abnormalities in severe dehydration people can have seizures and they can die.” Once people get into the 15 to 25 percent range of lost fluid volume, death occurs, he adds. (5)

Causes and Risk Factors of Dehydration
Dehydration happens when your body is losing more fluid and electrolytes than it is taking in and you don’t have enough left for your body to function normally. (2)

The adult human body is composed of as much as 60 percent water. It must maintain a delicate balance of fluids and electrolytes (including sodium chloride, potassium, calcium, and sodium bicarbonate) to maintain the health of cells and tissues. That water is primarily taken in through the gastrointestinal tract. Waste and excess fluid is removed by the kidneys and excreted as urine. Not having enough fluid coming in disrupts that balance, and compromises your body’s ability to regulate its temperature and function properly. (3)

A typical scenario where this might happen is when you’ve overdone it on a jog in the park on a particularly warm day. “The body is using fluid to cool itself when you are doing activities,” says Brian Schulz, MD, an orthopedic surgeon and sports specialist at Cedars-Sinai Kerlan-Jobe Institute in Los Angeles. “The sweat is what keeps your body at a regular temperature. As you are exerting energy, that is causing an increase in temperature of the body, and the body is trying to normalize that so that you do not overheat.”

Dehydration can happen to anyone, but some groups of people are especially vulnerable. This includes:

Infants and Children Youngsters can’t always tell you if they are thirsty, nor can they get a drink for themselves. On top of that, they lose a higher proportion of their fluids to fever, and they are more likely to experience severe diarrhea and vomiting. (3)

Older Adults The body’s fluid reserve decreases with age, as does your sense of thirst and the ability to conserve water in the body. Other age-related vulnerabilities include that increases urination and health conditions that may prevent you from being able to self-hydrate. (3)

People With Chronic Illnesses Health conditions that can increase how much you pee, such as uncontrolled diabetes or kidney disease, can increase your risk of dehydration. High blood pressure and diuretics can also cause you to urinate more, as can some s used to treat diabetes and heart failure. A vicious cycle can develop for people with diabetes in which dehydration pushes blood sugar levels higher, which increases urination further and depletes the body’s fluid volume. (3,6)

People With Stomach Viruses or the Flu Any illness that causes you to lose fluid through urination, vomiting, diarrhea, or simply not feeling like drinking anything can lead to dehydration if you aren’t careful. This includes the flu. (3,7)

People Who Work or Exercise Outside Particularly when it’s hot and humid, and your sweat can’t evaporate and cool you off as well during exercise, your risk of dehydration and heat illness increases. And it’s not just the heat. Exercising in dry environments, even if cold, can cause more moisture loss due to dry air (for example, doing alpine activities). 

People Who Drink Alcohol A cold beer may seem like a great idea on a hot summer day, but any type of alcohol decreases the amount of arginine vasopressin, an anti-diuretic hormone, in your blood. Therefore, you urinate more and can dehydrate more quickly, according to research. (8)

People on Low-Sodium Diets Having the right amount of sodium in your blood helps you to retain water in your body, says Levitan. Sweating can deplete you of sodium and other electrolytes.

Women Who Are Breastfeeding Nursing a child can put you at risk for dehydration. “You’re losing lots of extra fluids and electrolytes to make milk,” Levitan explains.

How Is Dehydration Diagnosed?
It’s important to look for the signs of dehydration before they escalate and medical attention is necessary. Caught early, the problem is often easily corrected. “The second that you feel dry mouth or a headache, that is a sign that you should start to take [a drink of] water,” says Dr. Schulz. Feeling faint, not sweating in areas where you would expect to sweat, peeing less than usual, and having any type of mental status changes are signs that a person is dehydrated. If drinking fluids doesn’t correct the problem, seek medical attention, he adds.

If that medical attention happens on the spot, it could be from a sports team medic or an emergency responder. Those medical professionals are likely to ask you about your symptoms and what led to them, do a physical examination, and check for low blood pressure. They may also check for racing heart rate or pinch your skin to see if it is less elastic than normal.

Prognosis of Dehydration
Most people recover completely from dehydration once they recognize the signs and address them. As mentioned, moving to a cooler area and drinking water or sports drink with electrolytes will work in many instances. Even cases that are severe enough to end up in the emergency room are usually cleared up within a few hours after intravenous fluids are administered, says Arkun. (2)

Duration of Dehydration
Dehydration typically clears up the same day that you address it with adequate fluid. However, dehydration caused by a stomach virus — which may come with vomiting and diarrhea — should resolve on its own after a few days. (2)

Treatment Options for Dehydration
Increasing fluid intake is the primary way to treat dehydration.

Fluid Options
If you’re seeking medical attention for dehydration, a medic may have you move to a shaded area and drink water or a sports drink like Gatorade that contains electrolytes, or you may be given ice chips to suck on. (2)

A person who is dehydrated and has uncontrolled vomiting for more than four to five hours — whether due to viral infection or another cause — should go to the emergency room. (4)

If dehydration is severe enough to warrant an emergency room visit, the first few diagnostic steps are similar. “We take their vital signs and that tells you a lot about what is going on,” says Arkun. “If they have a fast heart rate or if their blood pressure is low then that tells us that their fluid volume is depleted.” Once that is determined, he says, “We’re going to give them lots of intravenous fluids,” often with a 0.9 percent solution of sodium chloride. “We also do lab work and check their electrolytes levels for abnormalities.”

Greater intervention is rarely needed. “Once you provide fluids and for nausea, 9 times out of 10 they get well and will be able to go home in a couple of hours,” says Arkun.

Alternative and Complementary Therapies
Some commonly mentioned home remedies to combat dehydration — from consumer websites and blogs — include drinking chamomile tea or other noncaffeinated teas; drinking coconut water; or drinking lime juice in water with a pinch of  salt and a teaspoon of sugar. But there’s no scientific proof that these remedies work better than water.

Hydration with water is preferable.

If plain H2O isn’t your thing, Levitan says sugar and salt in water can also be helpful in restoring energy and electrolyte balance.

“Herbal teas are fine,” she adds. “I don’t think there’s any magic there. Listen, if somebody likes the way something tastes then they are going to drink it more than then they will drink just plain water.”

To complement your fluid of choice, avoid caffeinated coffee, teas and soft drinks, because caffeine is a fluid-shedding diuretic. (9,10)

How Much Water You Should Drink and the Stages of Dehydration
It’s not unusual for people to lose body fluid when they’re active, in a hot environment, or taking that increases urination. When medical professionals talk about dehydration, they often assess it based on the percentage of body fluid that has been lost. “At a 3 to 4 percent decrease you won’t feel too good, but you won’t get a whole lot more symptoms,” says Arkun. Most people can absorb that decrease in fluid volume without realizing it.

What Does Chronic Dehydration Look Like?
In fact, many people exist in a state of inadequate dehydration, sometimes called chronic dehydration. Nearly 55 percent of all U.S. schoolchildren and adolescents are inadequately hydrated, with boys and Black students at higher risk than others, according to a study from 2015. (11) The authors assessed hydration in 4,134 students over a period of three years based on the concentration of water in their urine.

Not getting enough fluids is linked to headaches, irritability, poorer physical performance, and reduced cognitive functioning in both children and adults.

How Much Water Do You Need to Drink a Day?
It’s hard to apply hard-and-fast rules to how much water everyone should drink on a daily basis to stay adequately hydrated, though. (Remember the old adage to drink eight glasses of water a day? It’s oversimplified.) Beyond considering any underlying health conditions, a person’s water needs vary according to their weight and body size, food and fluid sources, activity level, geographic location, and other factors.

The most recent guidelines from the National Academy of Sciences advise that adult men ages 19 to 70 should imbibe 3.7 liters (125 ounces) of water daily and adult women in that age range should take in 2.7 liters (91 ounces). (12) That means 15 cups of fluid per day for men and just over 11 cups per day for women. But again, it really depends on so many variables, including your age, weight, gender, and whether you’re pregnant or breastfeeding. 

RELATED: Yes, It’s Possible to Drink Too Much Water

Treating Heat Stroke: A Common Complication of Dehydration
Losing fluid volume can affect your body’s ability to keep itself cool, leading to heat illness — the heat being your core temperature, not the heat outside. (13)

“The body’s natural defense for heat production is sweat,” explains Kevin Coupe, MD, an orthopedic surgeon in The Woodlands, Texas, who specializes in sports . “When we sweat, that puts the water on our skin and then the outside environment evaporates it, dropping our temperature.” Hot, humid weather can disrupt this natural cooling process. “If the humidity is high then the water doesn’t evaporate. It just sits there, and the cooling mechanism is not nearly as efficient.”

Dr. Coupe describes the following three stages of heat illness, as outlined by the American Academy of Orthopaedic Surgeons (AAOS). (13)

Heat Cramps Most people suffering from heat illness are in this first stage, Having overheated, they are sweating profusely, feel hot to the touch, and experience muscle cramps — particularly in the extremities. If you’re having those symptoms, drink water, hit pause on your workout, and gently stretch your muscles to ease your heat cramps.

Heat Exhaustion If your body can’t cool down, systemic symptoms, such as confusion, nausea, excessive thirst, weakness, and headache might develop, says Coupe. Early on in heat exhaustion, the person will sweat profusely but their skin will be cool. As his or her body temperature rises, sweating will stop altogether, and the skin will become hot, dry, and red. Vomiting, seizures, and loss of consciousness can result, and the person’s core body temperature may reach 104 degrees F. At this stage it’s important to move them to a cool place, fan them, or apply ice to bring their temperature down, give them fluid if they are conscious, and seek medical attention.

Heat Stroke A person in this stage is critically ill, says Coupe. Once their core body temperature reaches 105 degrees F, organ, brain, and cell damage can occur. They can slip into a coma. Immediate medical attention is needed to avoid permanent injury or death. Before emergency services arrive, a person with heat stroke should be treated with an ice bath or ice packs to the arms, neck, and groin areas. Remove as much of the person’s clothing as possible. But, Coupe says, heat illnesses rarely progress to this stage.

Learn More About Treatment for Dehydration

Prevention of Dehydration
The No. 1 way to prevent dehydration is to drink fluids! Consult your healthcare team to find out what’s optimal for you. In general, during hot, humid days or other situations that deplete fluid (such as exercise or illness) take a sip of water or a hydrating fluid with electrolytes every 15 minutes, Levitan suggests. “That should keep you on task,” she advises.

Furthermore, avoid beverages that can have a diuretic effect, such as alcohol or caffeinated drinks, says Schulz.

If you take that causes you to urinate more often, make sure you are staying on top of your water intake, and talk to your doctor about how much fluid you should be consuming. Also, if you have diabetes or are at risk for it, keep your blood sugar levels stable to avoid dehydration. (3)

And know that there are many foods that can help stave off dehydration due to their high water content.

Finally, “Use common sense,” says Schulz. “If it’s extremely hot outside then pick times of day when it’s not going to be as hot if you’re going to be out doing activities. Make sure you’re rehydrating every 15 to 20 minutes and that you are taking in the fluids that allow your body to keep the right temperature and not overheat.” With a little vigilance, dehydration is preventable in most cases.

Learn More About How to Prevent Dehydration

Complications of Dehydration
Although dehydration usually clears up quickly when fluids are restored, sometimes it can leave lasting health effects, such as:

Muscle Damage A bout with heat exhaustion can cause short-term muscle damage. “It can result in muscle soreness and aches and pains for several days,” says Coupe. “The body can recover from it, but there is some physiological damage to structures of the muscles.”

Kidney Stones Inadequate hydration on an ongoing basis can also come with health risks, such as kidney stones. That’s because the minerals and salts that form the stones are contained in your urine, and the less fluid you have in your urine, the more likely the stones will develop. (14) Drinking an adequate amount of water can help decrease the likelihood they will form in the first place.

Constipation Not taking in enough fluid can result in hard, dry stools that move too slowly through the gastrointestinal tract, clinically called constipation. Adding more fluids and fiber to your diet can help reverse the problem. (15)

Research and Statistics: How Common Is Dehydration?
Dehydration is extremely common. Keep in mind:

At least 518,000 people are hospitalized in the United States each year for dehydration. (1)
About 10,000 of those who are admitted to the hospital for dehydration each year die there. (1)
Men are more likely to have inadequate hydration than women. The National Center for Health Statistics (NCHS) reports that as of 2012, men in the U.S. consumed 0.24 liters (L), or 8 ounces (oz) less than the recommended daily intake of water each day from all foods and liquids, while women consumed an average of 0.05 L (2 oz) more than the RDI each day. (16)
The same analysis found that seniors are more likely to have inadequate hydration than younger adults. Men over age 60 consumed 0.78 L (26 oz) less than the recommended daily intake of water each day in 2012, and women over age 60 drank 0.19 L (6 oz) less than is recommended. 
BIPOC Communities and Dehydration
The first step to avoid dehydration, of course, is to make sure that you are drinking enough water. However, Black, Indigenous, and People of Color (BIPOC) communities are drinking less of it than white people do, on average. The NCHS also reports Black American men and women consume 0.78 L (26 oz) and 0.29 L (10 oz) less than daily recommended intake levels. Hispanic American men and women drank 0.37 L (12.5 oz) and 0.12 L (4 oz) less than their respective recommended levels. However, white men drank the recommended amount and white women actually consumed 0.15 L (5 oz) more water than what was considered adequate. (16)

It’s no surprise then that Black and Hispanic adults were found in a prior study to have 40 percent higher odds of being inadequately hydrated than white adults. A study from 2017 looked at the type of water sources consumed, Black and Hispanic adults were more likely to be drinking bottled water (which has a cost attached to it), and white adults were more likely to drink tap water. Looking at income, the researchers found that higher-income adults were more likely to drink tap water than lower-income adults. (17)

To explain their results, the study authors pointed to previous research finding that Black and Hispanic adults were more likely to report that their local tap water was not safe to drink and that this was linked to drinking less water — whether bottled or tap — and more sugar-sweetened beverages. (17)

As mentioned, a separate study of school children ages 6 to 19 found that Black students were more likely than white students to be inadequately hydrated. (11)

Related Causes and Conditions of Dehydration
Several common symptoms of dehydration — fatigue, dizziness, confusion, nausea, and headache — are also possible signs of other common health conditions. “Sometimes in the summer, we are quick to blame things on dehydration but there are other more serious conditions that can look similar,” says Levitan. A heart attack is one of them, she says. Although chest pains are a common sign of a heart attack, so are cold sweats and a racing heart. In women especially, heart attack symptoms may include only fatigue and nausea and a lack of the “classic” chest pain symptoms. (18)

Signs of a stroke can be mistaken for dehydration as well. Severe headache, confusion, and dizziness are among the symptoms people experience. (18)

Dehydration can mimic signs of a migraine, too, says Levitan. Headache, confusion, nausea, and weakness often accompany migraine, just as they might dehydration. (19) But there’s a twist: “A migraine can actually be caused by dehydration,” adds Levitan.

The best indication that the health crisis is due to more than dehydration, she adds, is “If the person doesn’t respond relatively quickly to hydration.”

Learn More About Conditions That May Be Mistaken for Dehydration