How To Tell If Your Child Is Dehydrated

Dehydration means the body loses more fluids than it takes in and if it's not treated, it can become a serious issue. Babies and children are particularly vulnerable to dehydration because they have a higher activity level than adults, plus a high ratio of body surface area to mass. (This means that when a child sweats, they lose more of their body's water content than an adult.)

According to a national study from Harvard T.H. Chan School of Public Health, more than half of all children and adolescents in the U.S. are not getting enough hydration, with Black children and boys at the highest risk for dehydration.

Whatever brings it on, the signs of early dehydration in a child can be sneaky. In fact, a kid who needs more fluid may not even seem very thirsty, if at all. But because severe dehydration can have serious complications, it's important to know what to look for well before a child reaches that point. Here's what you need to know about the causes of child dehydration and how to prevent it.

What Causes Child Dehydration?

The most common causes of dehydration are fluid losses from the gastrointestinal tract, such as diarrhea, vomiting, or bleeding, or from the skin, such as fever or burns, says pediatrician Florencia Segura, MD, FAAP, a pediatrician at Einstein Pediatrics in Virginia.

It's not just fluid loss that can become a problem with dehydration. If vomiting is severe or prolonged, a child may lose the important electrolytes chloride, potassium, and sodium, which regulate fluid balance, maintain the blood volume required for healthy function, and assist with nerve impulse transmission and muscle contraction, says the American Academy of Pediatrics.

Less often, dehydration may be caused by a chronic condition. For example, the high levels of blood sugar in a child who has diabetes can cause them to urinate more often than usual.

How Much Water Should Children Drink?  

Every child will have their own fluid requirements—some children are simply thirstier than others, and they should all be encouraged to drink to quench their thirst, says Kelly Fradin, MD, FAAP, pediatrician, and author of "Parenting in a Pandemic: How to Help Your Family Through COVID-19."

When this isn't possible, Dr. Fradin recommends estimating fluid needs from a child's body weight. "For the first 10 kilograms (approximately 22 pounds) of weight, aim to provide 4 milliliters (about 0.13 ounces) per kilogram per hour; for the second 10 kilograms of weight, add 2 milliliters per kilogram per hour; and subsequently, about 1 milliliter per kilogram per hour," she says.

This equation adjusts for small babies who have bigger fluid losses because of their faster respiration and proportional body surface area and bigger fluid needs due to their fast metabolism, Dr. Fradin notes. These infants require more water per pound or per kilogram than adults.

Infants get all of their fluid needs from breastmilk or formula, which is normally no less than 720 milliliters per day. "It gradually increases to the adult needs which vary by sex and size but range from 2700 to 3700 milliliters per day," Dr. Fradin says.

Symptoms of Child Dehydration 

A dehydrated child may have fatigue, headache, decreased urine output, and elevated heart rate, says Dr. Fradin. Their capillaries may also be slow to fill. You can test this by pressing on the nail bed of one of their fingers until the nail whitens. If it takes more than two seconds for the nail to return to its normal pink color, the child is becoming dehydrated.

Another thing to look out for is decreased skin turgor. "If the skin on the thigh is pinched in a 'healthy' child, it will immediately return to its flat state when the pinch is released, but in a dehydrated child, the skin flattens more slowly after release," Dr. Segura explains.

When it comes to making a clinical diagnosis of dehydration, it's most objectively measured as a change in weight from baseline, adds Dr. Segura. But in most cases, a recent pre-illness weight is not available. "Various findings from the physical exam and the clinical history help assess dehydration," she says.

While the symptoms of dehydration don't generally vary with age, there are specific findings in infants, such as a "sunken fontanelle," says Dr. Segura. (The fontanelle is the gap between the bones in a baby's skull that enables the continued growth of their head.)

"When babies are dehydrated, the fontanelle on the top will look and feel caved in," Dr. Segura explains. Another indication of dehydration in babies is having less than four or five wet diapers per day and decreased tears, she adds.

It's typically easier to identify dehydration in older children simply because they have a greater ability to accommodate their fluid losses. "An older child will feel thirst and complain until their fluid needs are met whereas a baby can't often express their needs," explains Dr. Fradin.

Dr. Fradin points out that older children's kidneys are more mature and capable of conserving water more efficiently than babies who rely on adults to provide them with sufficient fluids and electrolytes.

What to Do If Your Child Is Dehydrated 

Almost every level of dehydration can be treated with fluids by mouth, which includes breastfeeding or bottle-feeding infants, says Dr. Segura.

"We recommend oral rehydration solutions such as Pedialyte or Enfalyte for young and older children because they give the body the right amount of water and salts," she says. These solutions work with the gut, transporting water to absorb the electrolytes and retain water better.  

Dr. Segura recommends giving a dehydrated child 5 ccs (1 teaspoon) of solution every two minutes, and to continue giving extra fluids if their child's vomiting or diarrhea continues. "The child can return to their regular diet once they are no longer dehydrated," she says.

Use commercial sports drinks with care, the American Academy of Pediatrics warns. Although they replace salts, they also contain large amounts of sugar which can worsen diarrhea. Instead, offer a plain water alternative of fruit juice diluted half-and-half with water or flat soda.

Sometimes dehydration can occur as a result of a sore throat because swallowing fluids can be difficult, so giving appropriate pain meds can help, adds Dr. Fradin. "I become very worried when children begin to feel dizzy as this can be a signal that their body's ability to compensate is inadequate," she says. "If a child is not urinating at least three times a day, that indicates that they are not taking in sufficient fluids."

How to Prevent Dehydration 

Understanding the causes and being aware of the signs of dehydration is important, but the best way to prevent it is to know how to stop it from happening.

To prevent dehydration in newborns, feed them regularly. Offer bottle-fed babies 1 to 3 ounces of infant formula or bottled, pumped breast milk every two to three hours.

It's advisable to nurse a breastfeeding newborn at least every two to three hours during the day and night. As babies grow, they tend to sleep longer between feeds. It's best to continue feeding even if your child has diarrhea or is vomiting because those extra fluids are required to replace what's being lost.

For older children, the American Academy of Pediatrics recommends offering frequent sips of clear liquids such as water or an oral electrolyte rehydration solution to a child with vomiting or diarrhea. Ice chips are another option if they don't feel able to drink. While it may be tempting to try to get a sick kid to guzzle a lot at once, it will likely make their symptoms worse. By building up to 1 ounce, then 2 ounces an hour, your child should be able to drink normally and avoid dehydration.

If it's very hot or humid, try to avoid taking your newborn or young infant outdoors; if you do venture out, stick to shaded areas to keep them cool. Don't forget that babies can overheat indoors if the room temperature is too high or they're wearing too many layers.

A Word From Verywell

The prospect of your child becoming dehydrated can be scary. However, ensuring that your baby or young child is taking in an adequate amount of fluid each day can help prevent dehydration. If you think your child might be dehydrated, reach out to their pediatrician and start getting them more fluids. If symptoms are severe, go to the emergency room or call 911.