Dehydration

Dehydration is when the body loses more water than it takes in, which can disrupt important processes that keep us healthy. It often happens because of too much sweating, health problems, or not drinking enough water. Even things like going underwater for long periods, called immersion diuresis, can increase the chance of getting sick for divers.

Most people can lose a small amount of water — about 3 to 4% of their total body water — without feeling too bad. But if someone loses between 5 to 8% of their body water, they might start feeling fatigued and dizzy. Losing more than 10% can make both the body and mind work poorly, and a person will feel very thirsty. If the body loses too much water — around 15 to 25% — it can be very dangerous.

Dehydration can also lead to hypernatremia, which means there is too much sodium in the blood. Over time, not drinking enough water can even help kidney stones form or lead to long-term problems with the kidneys. Usually, drinking water or special drinks called oral rehydration solutions can help with mild dehydration, but in serious cases, doctors might need to give fluids directly into the blood.

Signs and symptoms

When the body loses too much water, you might feel very thirsty and get headaches. Other signs include feeling tired, having no appetite, and peeing less. As dehydration gets worse, you might feel confused or even have seizures. Even a small loss of water, like 1–2% of your body’s water, can make it harder to think clearly. Older people may not feel as thirsty when they’re dehydrated, but they can still get tired and weak, especially in hot weather.

Cause

Dehydration happens when the body loses more water than it takes in. This can occur during hot weather, at high altitudes, or while doing long sports activities. Elderly people, young children, and those with chronic illnesses are especially at risk.

Medications can also cause dehydration as a side effect. Water leaves the body through sweating, vomiting, diarrhea, and other natural processes. Diseases that affect how the body manages water and sodium can also lead to dehydration.

Mechanism

The human body is mostly made up of water, from about 70–75% in newborns to less in adults. This water is found either inside cells (intracellular fluid) or outside cells (extracellular fluid), which includes blood.

When the body loses too much water, the concentration of dissolved particles increases. Special sensors in the brain detect this change and signal the release of a hormone called antidiuretic hormone (ADH). ADH helps the body hold onto water by increasing water absorption in the kidneys and narrowing blood vessels to maintain blood pressure.

Diagnosis

Dehydration happens when the body loses more water than it takes in through normal activities like breathing, urination, perspiration, diarrhea, or vomiting. When dehydration becomes severe, it can be very dangerous and might cause health problems.

Doctors look for signs of dehydration by checking the skin and other parts of the body. They might notice dry mouth, dry underarms, slow return of pinched skin to its normal shape, and sunken eyes. In more serious cases, people might feel dizzy or weak. Tests with blood and urine can also help show if someone is dehydrated.

Prevention

For everyday activities, feeling thirsty is usually a good sign that you need to drink more water. How much water you need can change based on your body size, how active you are, your age, and the weather. When you exercise or are in a hot place, you might need to drink more water than usual.

When it's hot or humid, or if you're working out hard, you can lose a lot of water through sweating. This can also make you lose important minerals like sodium. For most people, drinking water when you're thirsty is enough to stay safe during exercise. Sports drinks with a little sodium can help, but plain water is usually all you need to avoid getting dehydrated.

Treatment

Main article: Management of dehydration

"Rehydrated" redirects here. For the SpongeBob video game remaster, see SpongeBob SquarePants: Battle for Bikini Bottom – Rehydrated.

The best way to treat mild dehydration is to drink water and stop losing fluids. Drinking water helps restore the amount of fluid in your blood, and eating food also helps because about 22% of the water we get comes from food. As you rehydrate, your urine will go back to normal.

In some cases, you might need to drink special solutions that have water and important minerals called electrolytes. For mild dehydration, it’s usually best to drink these solutions because it’s simple and doesn’t need special equipment. For more serious cases where someone can’t drink or is feeling very weak, doctors might give fluids directly into a vein, but this is done carefully in a medical setting.

Prognosis

The outlook for dehydration depends on what caused it and how severe it is. For mild dehydration, drinking water usually fixes the problem. However, long-term dehydration, like from hard physical work or not feeling thirsty often enough, can affect kidney health. Older people who become dehydrated may face confusion, infections, falls, and slower healing of wounds. For children with mild to moderate dehydration, drinking fluids is enough to help them fully recover.

Main article: chronic kidney disease