Merck Manual

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Reviewed/Revised May 2022 | Modified Sep 2022
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Everyone needs water and electrolytes Overview of Electrolytes Electrolytes are minerals that circulate in your blood. These minerals are also in your stomach juices, in your stool (poop), in your urine, and inside your body's tissues. Salt (sodium) is... read more (minerals, such as sodium and potassium, that help with many body functions) to be healthy. Normally, your body automatically balances your level of water and electrolytes. Drinking gives you what you need, and being thirsty tells you when you need to drink.

What is dehydration?

Dehydration is having too little water in your body.

  • Dehydration happens when your body loses more water than it takes in

  • Certain medicines or diseases (such as diabetes) that make you urinate a lot can cause dehydration

  • Throwing up, diarrhea, and sweating a lot from hot weather or heavy exercise also can cause dehydration

  • Older people and young children are more likely to become dehydrated

  • Severe dehydration makes you confused, light-headed, and weak

  • Dehydrated people need fluids and electrolytes either by drinking or sometimes by vein (IV)

  • Without treatment, severe dehydration can cause death

What causes dehydration?

You get dehydrated when you lose fluid and don't replace enough of it.

Common causes of losing fluid:

  • Throwing up

  • Diarrhea

  • Urinating too much because of medical problems such as diabetes

  • Taking medicines that make you urinate more (diuretics, also called water pills)

  • Sweating a lot, particularly in bad heat waves or if you're working or exercising a lot in hot weather

Usually if you lose fluid, you'll just drink more to replace it. But sometimes you can't drink enough fluid.

Common reasons people can't drink enough fluid:

  • There isn't any water around, such as in the desert

  • They can't tell people they're thirsty, such as babies or old people who are confused or had a stroke

  • They can't get their own water, like people who can't get out of bed because they're sick

  • They're vomiting a lot

What are the symptoms of dehydration?

Symptoms of mild to moderate dehydration:

  • Being very thirsty

  • Having a dry mouth

  • Urinating less

Symptoms of severe dehydration:

As you lose water, your blood becomes more concentrated and has more electrolytes (such as sodium) in it.

How do doctors tell if I am dehydrated?

Doctors can usually tell you're dehydrated from your symptoms and a physical exam. Sometimes, they'll do blood and urine tests.

How do doctors treat dehydration?

When possible, doctors treat the cause of your dehydration. For example, if you're vomiting or have diarrhea, they'll have you take medicine to stop it. At the same time, they'll have you replace the lost water in your body.

For mild dehydration:

  • Drinking water may be all you need

  • Sometimes, particularly for children, doctors use a special mix of water, sugar, and minerals called oral rehydration solution

Sports drinks aren't harmful, but they aren't the best liquid to treat dehydration. They have too much sugar and don't have the right balance of electrolytes.

For moderate or severe dehydration:

  • Doctors will have you drink an oral rehydration solution

  • If you can't drink enough or are severely dehydrated, you'll get electrolytes and fluids directly into your vein (through an IV)

How can I prevent dehydration?

  • On hot days and before, during, and after heavy exercising, drink plenty of fluids, either water or sports drinks

  • Keep an eye on older people in hot weather, particularly if they live alone, and give them water or make sure they can get water when they need it

People used to think taking salt tablets helped. But salt tablets aren't necessary and can be harmful.

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