Signs of Dehydration in a Baby

The short answer

Dehydration in a baby shows up in nappy output, tears, mouth, eyes, the soft spot on the head, and alertness. The NHS lists the signs in a baby as a sunken soft spot (fontanelle) on top of their head, sunken eyes, few or no tears when they cry, fewer wet nappies than usual, and being drowsy or irritable. The American Academy of Pediatrics splits its warning signs into two groups and tells parents to notify the pediatrician immediately if any of them develop. Its complete mild to moderate group is: plays less than usual, urinates less frequently (for infants, fewer than six wet diapers per day), parched dry mouth, fewer tears when crying, sunken soft spot of the head, and a change in stools, loose if diarrhoea is the cause and decreased if the loss is from vomiting or low intake. Its complete severe group: very fussy, excessively sleepy, sunken eyes, cool discoloured hands and feet, wrinkled skin, and urinating only one to two times per day.

Two of those severe items are routed differently by the two bodies. The AAP heading over both groups says to notify the pediatrician immediately. The NHS Dehydration page puts being sleepier than normal or difficult to wake, and skin that feels cold, in its call 999 or go to A&E list instead. Where two authorities disagree, act on the more urgent one. A baby who is difficult to wake, or whose skin feels cold, is an emergency call now, not a message left for the surgery.

You are not expected to work out which group your baby is in. That is a clinician's assessment. Your job is to notice the change and make the call.

When to get help now

These come from the NHS, the American Academy of Pediatrics and healthdirect Australia, three bodies with their own thresholds and phone numbers, not one standard. Where a list below is shorter than its source, this article says so at that point and Sources links the whole thing.

Call 999, 911 or your local emergency number, or go to an emergency department, if any of the following is true. Each item comes from an emergency tier on its own source list. NHS items below are the NHS Dehydration page's call 999 or go to A&E list unless another page is named, and all five of that list's bullets are here.

• Your baby's skin, lips or tongue look blue, grey, pale or blotchy. The NHS bullet reads on the cited page: "blue, grey, pale or blotchy skin, lips or tongue – on brown or black skin, this may be easier to see on the palms of the hands or soles of the feet" (NHS, Dehydration, call 999 or go to A&E). The second half tells you where to look on brown or black skin. It is part of the sign, not a footnote to it.
• Your baby's skin feels cold (NHS).
• Your baby is having difficulty breathing, or is taking lots of quick breaths (NHS).
• Your baby is sleepier than normal or difficult to wake (NHS).
• Your baby is confused (NHS). The NHS diarrhoea and vomiting page words the equivalent 999 item as being confused or not responding as usual.
• Your baby cannot be woken up, or is not moving (AAP symptom checker, Vomiting 0 to 12 Months, "Call 911 Now").
• You think your baby has a life-threatening emergency (AAP symptom checker, "Call 911 Now"). All three items on that list are here.
• Your baby is hard to wake up, or is not alert when awake (AAP symptom checker, "Go to ER Now"). That list has seven items and only these two are quoted here. The other five cover a stiff neck, blood or bile in the vomit, suspected poisoning and a swallowed object.
• Your baby's vomit is yellow-green or green, contains blood, or looks like ground coffee (NHS, Diarrhoea and vomiting, call 999 or go to A&E). That page's 999 list is longer than the part quoted here. Its other bullets repeat the blotchy-skin and breathing signs and add stiff neck with light sensitivity, sudden severe headache or tummy ache, and swallowed poison.

Get urgent advice now, the same day, from your pediatrician, NHS 111, or your local out-of-hours service, if any of the following is true. NHS items are from the NHS Dehydration page's urgent GP appointment or NHS 111 tier, and all six of its bullets are below, including the two the NHS words for the adult reader.

• Your baby has a soft spot on their head that sinks inwards (NHS). The AAP puts a sunken soft spot in its mild to moderate group and says to notify the pediatrician immediately. healthdirect says severely dehydrated babies may have a sunken fontanelle, and its instruction for severe dehydration is the most urgent of the three: "If you are severely dehydrated, get urgent medical attention. See your doctor or go to a hospital emergency room."
• Your baby has few or no tears when they cry (NHS).
• Your child seems drowsy (NHS). The NHS bullet reads "you're feeling unusually tired (or your child seems drowsy)".
• Your baby has fewer wet nappies (NHS). The NHS bullet reads "you have dark yellow pee or you're peeing less than normal (or your baby has fewer wet nappies)".
• You feel dizzy when you stand up and it does not go away (NHS). Written for the adult reader, not for a baby, and here so the list is not cut short.
• Your baby is breathing quickly or has a fast heart rate (NHS). healthdirect puts breathing fast and a fast heart rate among its severe dehydration symptoms, not its mild to moderate ones, and severe dehydration on that page routes higher than the same day: urgent medical attention, see your doctor or go to a hospital emergency room.
• Your baby has sunken eyes. The NHS lists these among the baby signs without attaching a tier. The AAP puts them in its severe group under notify the pediatrician immediately. healthdirect lists them as a severe dehydration symptom, and its routing there is the one to act on: urgent medical attention, see your doctor or go to a hospital emergency room.
• Your baby has a dry mouth, absent tears, depression of the "soft spot" or decreased urination. The AAP says to call your pediatrician immediately if these occur (AAP, Causes of Vomiting in Infants and Children).
• Your baby has any of the AAP warning signs listed above. The AAP says to notify the pediatrician immediately (AAP, Signs of Dehydration in Infants and Children).
• You suspect your baby is dehydrated. The AAP symptom checker item under "Call Doctor or Seek Care Now" reads "Dehydration suspected. No urine in more than 8 hours, dark urine, very dry mouth and no tears." Suspected dehydration is the trigger. The four things after it describe what it can look like, and you do not have to tick all four to call.

The next seven are the cited call 111 now list from the NHS diarrhoea and vomiting page.

• You are worried about a baby under 12 months old.
• Your child stops breast or bottle feeding while they are ill.
• Your child is under 5 years old and has signs of dehydration, such as fewer wet nappies.
• You or your child aged 5 years or over still have signs of dehydration after using oral rehydration sachets. Written for ages 5 and over, so it does not apply to a baby, and here so the list is not cut short.
• You or your child keep being sick and cannot keep fluid down.
• You or your child have bloody diarrhoea or bleeding from the bottom.
• You or your child have diarrhoea for more than 7 days, or vomiting for more than 2 days.

And from healthdirect:

• Your baby is under 6 months old and has signs of mild dehydration. healthdirect says to see your doctor as soon as possible, because young babies can go from mild to severe dehydration very quickly.

If you are worried about your baby right now, you do not need a reason that satisfies anyone. Call your pediatrician, your local out-of-hours service, or your emergency number. Trusting your instinct is the correct response.

Why the clock runs faster in babies

healthdirect, an Australian government-funded health advice and information service, states that babies and young children have a higher chance of becoming dehydrated than adults, and that young babies can go from mild to severe dehydration very quickly. That sentence is why the under 6 months bullet exists. It names five things that dehydrate a baby quickly: vomiting, fever, diarrhoea, being unwell for any reason, and not feeding or drinking enough. Three of those five involve no stomach bug.

Nappies

Output is what the sources put numbers on. healthdirect describes mild dehydration in babies and toddlers as fewer wet nappies, or nappies not as wet as usual, so a nappy can be technically wet and still be a drop in output. The AAP gives fewer than six wet diapers per day the same instruction as every other warning sign on that page: notify the pediatrician immediately. Know when the last properly wet nappy was, and how it compared, before you phone.

Sign by sign

Soft spot. The fontanelle is the soft area on a baby's head where the skull bones have not yet joined. Three bodies place a sunken one in three different bands, as above. Do not average them. Act on the highest. And a normal-looking fontanelle does not rule dehydration out, so it is not a test that settles the question.

Tears and mouth. healthdirect's dry mouth, lips and tongue entry is written for all ages. The AAP list is written for infants and children.

Skin. WHO counts a skin pinch going back very slowly, two seconds or more, among four severe signs, and requires at least two of the four together. Do not attempt it at home. If you are close enough to a baby to be considering it, you are close enough to phone someone.

Alertness. The NHS puts drowsy or irritable among the baby signs and a child seeming drowsy on its urgent GP or NHS 111 list, but sleepier than normal or difficult to wake, and confused, in its call 999 group. The AAP severe group has very fussy and excessively sleepy under notify the pediatrician immediately, while its symptom checker puts "can't wake up" under "Call 911 Now". WHO lists lethargy or unconsciousness first among its four severe signs. Read that spread from the top. A baby who is difficult to wake is an emergency call on two of those lists, not something to watch for another hour.

General guidance, not your baby

Everything above is a plain-English account of what named health bodies publish. It cannot account for your baby's weight, age, prematurity, feeding history, conditions or medications, which are exactly the things that change the answer.

This article contains no rehydration recipes, no fluid amounts and no medicines. Rehydration in an infant is prescribed by weight and clinical assessment, so ask your pediatrician or pharmacist what is right for your baby.

Related baby-care guides

Continue with fever in babies when to call and how often should a newborn feed.

Sources

Every claim above names its source page, at the tier that page uses. Open the page itself for any list quoted here only in part.

• NHS, Dehydration (last reviewed 1 May 2026, next review due 1 May 2029). Signs in a baby, and both the 999 and the urgent GP or NHS 111 tiers.
• NHS, Diarrhoea and vomiting (last reviewed 21 December 2023, next review due 21 December 2026). The 999 vomit-colour items, the wording "are confused or not responding as usual", and the seven call 111 now items.
• AAP, HealthyChildren.org, Signs of Dehydration in Infants and Children (last updated 24 September 2019, adapted from Caring for Your Baby and Young Child: Birth to Age 5, 6th Edition). The six-item mild to moderate and six-item severe groups, and the notify-the-pediatrician-immediately heading over both.
• AAP, HealthyChildren.org symptom checker, Vomiting (0 to 12 Months) (Barton Schmitt MD, FAAP). The "Call 911 Now", "Go to ER Now" and "Call Doctor or Seek Care Now" items.
• AAP, HealthyChildren.org, Causes of Vomiting in Infants and Children (last updated 29 December 2024, AAP Section on Gastroenterology, Hepatology and Nutrition). Dry mouth, absent tears, depression of the "soft spot" and decreased urination, with the instruction to call your pediatrician immediately.
• healthdirect, Australia, Dehydration (last reviewed July 2024). A government-funded Australian health advice and information service. Higher risk in babies, what dehydrates them quickly, nappy wetness, the mild to moderate and severe lists, and the under 6 months advice.
• World Health Organization, Diarrhoeal disease fact sheet (7 March 2024). A public fact sheet, not health-worker guidance. Severe dehydration (at least two of lethargy or unconsciousness, sunken eyes, unable to drink or drinks poorly, skin pinch going back very slowly at two seconds or more) and some dehydration (two or more of restlessness or irritability, sunken eyes, drinks eagerly or thirsty).

Independent guidance, not medical advice. We do not diagnose or recommend treatments or doses. For any concern about your baby, contact your pediatrician or local emergency service.