Under normal conditions, we all lose some body water every day in our sweat, tears, urine, and stool. Water also evaporates from skin and leaves the body as vapor when we breathe. We usually replace this body fluid and the salts it contains with the water and salts in our regular diet.

Sometimes, however, kids lose large amounts of water and salts through fever (more water evaporates from the body when body temperature is increased), diarrhea, vomiting, or long periods of exercise with excessive sweating. Some illnesses might also prevent them from taking fluids by mouth. If they're unable to adequately replace the fluid that's been lost, kids can become dehydrated.

Recognizing Dehydration

If your child has fever, diarrhea, or vomiting, or is sweating a lot on a hot day or during intense physical activity, watch for signs of dehydration, which can include:

• dry or sticky mouth
• few or no tears when crying
• eyes that look sunken into the head
• soft spot (fontanelle) on top of baby's head that looks sunken
• lack of urine or wet diapers for 6 to 8 hours in an infant (or only a very small amount of dark yellow urine)
• lack of urine for 12 hours in an older child (or only a very small amount of dark yellow urine)
• dry, cool skin
• lethargy or irritability
• fatigue or dizziness in an older child

Preventing Dehydration

The best way to prevent dehydration is to make sure kids get plenty of fluids when they're sick or physically active - they should consume more fluids than they lose (from vomiting, diarrhea, or sweating).

How to keep them hydrated can depend on the circumstances. For example, a child with a sore throat may become dehydrated due to difficulty drinking or eating. Easing the pain with acetaminophen or ibuprofen may help, and cold drinks or popsicles can soothe a burning throat while also supplying fluids.

Infants with blocked noses who have trouble feeding can be helped by flushing their nostrils with saltwater (saline) nose drops and suctioning out the mucus with a bulb syringe.

Fever due to various infections is a factor in dehydration and can be controlled with medications or lukewarm baths.

It's important that kids drink often during hot weather. Those who participate in sports or strenuous activities should drink some extra fluid before the activity begins. They should also drink at regular intervals (every 20 to 30 minutes) during the course of the activity and after it ends. Ideally, sports practices and competitions should be scheduled for the early morning or late afternoon to avoid the hottest part of the day.

Thirst is not a good early sign of dehydration. By the time a child feels thirsty, he or she may already be dehydrated. And thirst can be quenched before the necessary body fluids have been replaced. That's why kids should start drinking before thirst develops and consume additional fluids even after thirst is quenched.

Read more on dehydration.