Picture this: You were just trying to soak up the sun and outdoor fun. You didn’t even notice how long it’d been since you had anything to drink. But now something just doesn’t feel right. You’re feeling really tired. And your head is hurting out of nowhere. Then it hits you. You may be dehydrated.

Dehydration happens when you lose more water than you take in. This makes it harder for your body to work properly. And it can happen when you combine hot weather, extra activity and all that sweating. When you start feeling dehydrated, you want to act fast. Even a slight case can be serious. It can affect your blood pressure, heart rate and temperature.

Here’s the good news. You can learn how to tune into your body and make sure you’re getting all the water you need. Read on.

Signs and symptoms: How can you tell you’re dehydrated?

“I tell patients to listen to your body,” says Neil Gokal, MD. He’s the medical director of Southwest Medical, part of Optum, in Las Vegas. “When you feel thirsty, drink something.”

You can also watch for¹:

• Tiredness
• Headache
• Dizziness or weakness
• Confusion
• Dry mouth, dry cough or bad breath
• Fast heart rate with low blood pressure
• Loss of appetite (sometimes with a sugar craving)
• Red skin
• Swelling in your feet
• Muscle cramps
• Heat or chills
• Constipation
• Peeing less often
• Dark-colored pee (it should be a pale, clear color)

For very young children and infants, the symptoms may be a little different.² Keep an eye out for:

• No tears when crying
• Dry mouth and tongue
• A dry diaper for three hours or more
• Sunken eyes and cheeks
• Sunken soft spot on the top of the head
• Being tired or cranky

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Why you should care about dehydration

Dehydration can be life-threatening. Your body works best when everything’s in balance, says Dr. Gokal. But dehydration can cause your blood to lose important minerals. Those minerals include calcium and potassium. They help your organs work well.

When the minerals are low, your muscles may cramp. Or you may have heartburn.³ Really low levels can hurt your nervous system. If you don’t get care, you may have seizures or even brain damage.

One of the biggest dangers is hypovolemic shock. That’s when your blood pressure and oxygen levels drop. This happens due to low blood volume. There’s not enough blood for your heart to pump through your body. This can make your organs stop working. You’ll need emergency care at a hospital.

When you have a fever and you can’t drink because your stomach’s upset, you’re throwing up or have diarrhea, get medical care right away, Dr. Gokal says. Call 911 if you have any of these symptoms⁴:

• Weakness
• Dizziness or fainting
• Drowsiness or confusion
• Diarrhea with blood or mucus
• Blood in your vomit

Learn more about the risks of heat exhaustion and heatstroke.

How do you care for dehydration?

If you feel symptoms coming on, take these steps:

• Drink fluids, especially water. If you find it difficult to drink, start with slow sips and then drink a little more.

• Replace minerals. Sports drinks are a good source. For children, you can try drinks like Pedialyte.⁵ Skim milk is another good choice. So are water-rich fruits like cantaloupe, strawberries, watermelon, bananas, grapes and oranges.⁸

• Stay away from caffeine and alcohol. Both can make you pee more and lose even more fluids.

• Cool down and relax. Get out of the sun and rest for a while. The cooler you are, the less you sweat and the less dehydrated you may become.

Who’s at risk of dehydration?

Anyone can become dehydrated, but some people have higher risk¹:

Adults over 65. They already have less water in their bodies. And their sense of thirst may not be as strong.⁶ Plus, they may be taking medicines that can make them pee or sweat more, says Dr. Gokal.

Young children. Little kids are at greater risk because their bodies make more heat. They sweat less than grown-ups, too.⁷ Infants and young children are also more likely to throw up and have severe diarrhea. That makes them lose even more fluids.¹

People with long-term medical problems. Diabetes and certain lung or kidney problems can make you sweat and/or pee more than normal. That can lead to water loss. And people with memory loss or dementia may just not remember to drink enough.⁶

People who exercise or work outdoors. The harder you work or play on a hot day, the higher your risk. Athletes, construction workers and gardeners should be careful.

The takeaway

It’s simple: Beat the heat with plenty of water. “Staying well hydrated is important and healthy for all of your organs,” says Dr. Gokal. “That includes your heart, brain, kidneys and your largest organ, your skin.” So, when the temperature goes up, go inside or find a nice shady spot. Sit down for a while and pour yourself a cold glass of water.