What Really Happens to Your Body When You're Dehydrated

The effects of dehydration can be seen across your entire body, from your brain to your skin.
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What Really Happens to Your Body When examines the head-to-toe effects of common behaviors, actions and habits in your everyday life.

There's endless advice out there about leading a healthy lifestyle, and staying hydrated is one of the basics that gets repeated again and again.


Perhaps you're wondering what all the fuss is about.If you get everything else right, how important is hydration, really?

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In a word: very.

"From a structural or functional standpoint, water is a detergent and cleaning agent for our bodies," says Zach Bush, MD, a physician who specializes in internal medicine, endocrinology and hospice care.

Water is needed by every cell in your body to function properly, he explains, and is vital in helping our bodies work through the toxins we all breathe and eat every day.

Read on to discover dehydration's effects on your body and tips on how to keep your fluid intake where it needs to be.

Your Brain

When your body becomes dehydrated, your cells send a signal to your brain, which tells you that you're thirsty. But dehydration affects your brain in more surprising ways, too.


Although the mechanism isn't fully understood, dehydration is linked to a decrease in mood and cognitive performance.

A June 2013 review in the Journal of the American College of Nutrition revealed that a dehydration level of just 2 percent was enough to impair performance in tasks that required attention, psychomotor and immediate memory skills.


And although it was small, a February 2012 study published in the Journal of Nutrition found that even mild dehydration was enough to cause mood disturbances.

Dehydration can also cause problems in the brain when electrolyte levels fall too low. Electrolytes are minerals like potassium and sodium that help the electrical signals pass between cells.


If you are too low in electrolytes, you can experience a breakdown or disruption in these signals, which can cause involuntary muscle twitching and even seizures, according to the Mayo Clinic.


Dehydration in Sports Performance

Dehydration can significantly impact an athlete's performance; research suggests that loss of fluid equal to 2% of body mass is sufficient to cause a detectable decrease in performance, as outlined by Sports Dietitian Australia.

Dehydration can cause an increase in an athlete's heart rate and body temperature, as well as an increased perception of how hard the exercise feels, especially when exercising in the heat.

While sports dehydration symptoms may look different in individuals, some of the more common symptoms include shortness of breath, flushed skin and dizziness, according to the Cleveland Clinic.

Your Kidneys and Urinary System

When you're dehydrated, your cells send a signal to your hypothalamus, which releases a hormone called vasopressin, known as the antidiuretic hormone (ADH). This hormone tells the kidneys to remove less water from the blood, which leads to peeing less and a darker, more concentrated urine.


The kidneys are the main filter for your blood, and without adequate fluid, they can't expel the natural breakdown products and toxins from your bloodstream, Dr. Bush says. "Amazingly, your kidneys are capable of moving as much as 55 gallons of fluid a day."

If you are consistently dehydrated over long periods of time, your kidneys have to work extra hard. This can cause something called acute kidney injury, a form of damage that puts you at higher risk for kidney disease, according to the National Kidney Foundation.


What's more: "Lack of fluid intake can be a major contributor to kidney stone formation," Julie Stefanski, RDN, LDN, registered dietitian and spokesperson for the Academy of Nutrition & Dietetics, tells LIVESTRONG.com. People who live in warm, dry climates and those who sweat a lot may be at higher risk than others, according to the Mayo Clinic.

Your Blood

Your body needs fluid to make blood, so when your fluid levels drop, so does your blood volume.


"The bloodstream needs adequate fluid within the body to maintain an appropriate blood pressure," says Stefanski. Dehydration can lead to hypotension, or low blood pressure, which can cause you to faint.

At an extreme level, this can lead to an emergency condition called hypovolemic shock, where low blood volume leads to a big drop in blood pressure and the amount of oxygen in the blood, according to the U.S. National Library of Medicine. The heart is unable to pump enough blood around the body, which can lead to organ failure.


As your blood gets thicker, your body increases your heart rate and respiratory rate to compensate, essentially putting the body into a stress state.

"It's not unusual to then experience things like headache, fatigue, eye strain, decreased sex drive and decreased sleep quality, because the brain is in the fight-or-flight state," Dr. Bush says.

Additionally, dehydration can affect blood glucose levels, causing your blood glucose to spike, especially if you have diabetes. Dehydration causes the sugar in your blood to become more concentrated, which can be difficult to manage, per the CDC.


Young children and older adults have lower water levels and are more at risk for dehydration, according to the Academy of Nutrition and Dietetics.

Your Digestive System

Your gut needs adequate hydration to function properly. Water is needed for optimal motility (the movement of waste through your digestive system) and gut health.

"Without regular intake of fluids, bowel movements can be hard and difficult to pass," Stefanski says.

Dehydration can also damage the mucosal lining of the gut and your microbiome, which are important to both your digestion and your overall health.

Your Skin

Although you may not realize it, your skin is actually the largest organ in your immune system, Stefanski says. Healthy skin acts as a natural barrier against germs from our environment, but insufficient fluid intake can cause cracked lips and dry skin, where pathogens can enter.

Good hydration is essential for healthy skin. Although a small sample size, an August 2015 study in Clinical Cosmetic and Investigational Dermatology found a positive correlation between skin health measurements and hydration.


Dehydration Statistics and Information

  • Dehydration is common in elderly adults; It has been reported to occur in 17% to 28% of older adults in the U.S., per May 2021 research from StatPearls.
  • People with chronic illnesses that cause them to urinate or sweat more often, including diabetes, cystic fibrosis or kidney problems, are at a greater risk for dehydration, per the U.S. National Library of Medicine.
  • While the CDC does not have defined water intake recommendations, adults are encouraged to maintain between 2-3 L per day. People engaged in more physical activity need to drink more water compared to those who lead sedentary lifestyles.
  • In infants and young children, symptoms of dehydration can include crying without tears, no wet diapers for 3 hours or more, drowsiness and irritability.
  • Dark yellow urine can signal that your body is dehydrated, per UC San Diego Health.
  • Research suggests that people who get too little sleep are more likely to be dehydrated, according to a February 2019 study in Sleep.

So, How Much Water Do You Need?

A typical adult needs between 11.5 to 15.5 cups of water per day, according to the Academy of Nutrition and Dietetics. The average person takes in around 20 percent of their water needs through food, which alters these measurements to be from about 9 to 12.5 cups per day.

Hydration Tips

1. Don't Wait to Be Thirsty

Stefanski says everyone has differing levels of thirst instinct, which can mean you drink less than you need. "Rather than relying on thirst, schedule times throughout the day to drink a large glass of water," she says.

Remember: If you feel thirsty, you're already dehydrated.

2. Check Your Pee

Take cues from your bathroom breaks.

"Experts recommend that we should all be drinking enough to urinate every three to four hours. Urine should be a light yellow color," Stefanski says. "If you're not urinating at all or your urine is dark in color, you may not be drinking enough."

3. Jazz Up Your Water

Any fluid counts toward your overall fluid intake, so if you don't like plain water, mix it up. Add lemon slices and cucumber to plain water to make it more interesting, or make a cup of tea. Herbal tea makes a good replacement for plain water, but Stefanski warns that it's important to check for interactions if you take medications or have a chronic medical condition.

4. Watch Out for Caffeine and Alcohol

Although that cup of coffee or cocktail technically count toward your daily quota, caffeine and alcohol are diuretics, meaning they can cause you to actually lose water. So make sure to balance your boozy drinks with at least the same amount of H2O.


5. Eat Your Water

It's not just about water. "A lot of the effective hydration we get is actually through our food," says Dr Bush. "So things like cucumber, celery — these are powerful ways to get water into the body more effectively than a glass of water."

Consuming water-rich fruit and vegetables is a good way to increase your hydration levels while boosting your vitamin, mineral and fiber intake.

6. Paleo or Keto? Add More H2O

High-protein diets can be dehydrating, so it's especially important to hydrate regularly if you're following a paleo or keto plan.

"If you are on a protein-rich diet, you need to really work to increase the amount of water-carrying veggies in your diet to offset the potential dehydrating effect of protein," Dr. Bush says.




Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.

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