Understanding Infant Thermoregulation and Why Newborns Lose Heat Quickly

By Birth & Baby University · Last updated: October 2026 · 7 min read

Newborns arrive wet, small and suddenly responsible for keeping themselves warm. The reasons babies lose heat quickly, and the habits that protect them, are among the best-established parts of newborn care. They also sit awkwardly beside everyday advice that says “bundle up the baby,” even though overheating is also a danger. Postpartum doulas help families make dozens of small temperature decisions: what to wear, where to hold the baby, when to cuddle skin to skin and when a temperature reading calls for a phone call. This article reviews what a technical brief hosted by the World Health Organization, European newborn health standards, a Cochrane review and the American Academy of Pediatrics say, and where they differ.

Key takeaways

Quick answer: newborns lose heat faster than adults and have limited ability to generate it. The first hours and days after birth are the highest-risk period for both too-cold and too-hot temperatures. Drying, skin-to-skin contact, appropriate clothing and a comfortable room are the main protections. A baby 3 months old or younger with a rectal temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher needs a call to the pediatrician immediately.

• A Do No Harm technical brief hosted by WHO defines neonatal thermal stability as a body temperature between 36.5 and 37.4 degrees Celsius, defines hypothermia as below 36.5 and hyperthermia as above 37.5, and says the first 12 to 72 hours carry the highest likelihood of either problem.
• The European Standards of Care for Newborn Health give a normal axillary temperature as 36.5 to 37.5 degrees Celsius, so published ranges differ slightly at the upper end.
• The same brief lists drying immediately, skin-to-skin contact, early breastfeeding, delaying the first bath and dressing the baby appropriately for the environment among its thermal protection practices.
• A Cochrane review of early skin-to-skin contact in healthy newborns found that it supports breastfeeding, but its temperature results were of low-quality evidence and its authors called for larger trials.

What the research says

Why heat loss is a problem. The Do No Harm technical brief on thermal protection (hosted on WHO’s website; the PDF is dated July 2019) says all newborns are vulnerable to hypothermia, particularly in the first hours after birth, and that hypothermia is associated with complications including a need for respiratory support, low blood sugar, low blood pressure and late-onset sepsis. It points to usual practices that cause heat loss: not drying the baby, leaving them uncovered, shortening or not starting skin-to-skin contact, and delaying breastfeeding. The brief describes the high surface-area-to-body-mass ratio of small and low birth weight babies and their limited brown fat. Much of its data come from low-resource settings. It reports a study in Nepal in which most babies cared for without drying had temperatures below 36 degrees Celsius at 2 hours after birth, and a randomized trial in Uganda in which babies bathed within an hour of birth were nearly three times as likely to have hypothermia at 70 minutes. These figures illustrate the physiology, but they are not rates to expect in a well-resourced home or hospital.

The same brief stresses the other side. Hyperthermia, defined as above 37.5 degrees Celsius, can result from a room that is too warm, sun exposure, a radiant heater or too many layers, and the brief says dehydration is a common cause of elevated temperature in newborns. Its table of practices recommends a warm delivery room of about 25 degrees Celsius, immediate drying, skin-to-skin contact, breastfeeding within an hour, delaying the first bath to more than 24 hours after birth, and dressing and wrapping the baby appropriately. For healthy newborns it says to dress them with clothing appropriate for ambient temperature, generally 1 to 2 layers more than adults, plus a hat. The brief presents this as WHO guidance for newborn care, and it should not be treated as sleep-time advice. Safe sleep guidance differs: the AAP’s safe-sleep summary (How to Keep Your Sleeping Baby Safe, updated September 2026) says to dress a baby in only one more layer than an adult would wear and not to put a hat on an indoor baby once home from the hospital, because overheating can increase SIDS risk. The two documents serve different purposes (facility newborn care and low-resource settings versus sleep in US homes), but the layer and hat advice conflicts on its face, so teach the AAP version for sleep and the warm-chain steps for the first hours. Overheating and other sleep rules are covered in Safe Sleep Recommendations: What Every Postpartum Doula Must Know.

What counts as normal. The European Standards of Care for Newborn Health state, in their standard on temperature management, that normal axillary temperature is defined as between 36.5 and 37.5 degrees Celsius by international bodies, that variation from normal is more common in preterm and ill infants, and that both low and high body temperatures are associated with adverse outcomes. They grade the recommendation that parents are informed about ideal temperature and invited to measure their infant’s temperature as high-quality evidence. The technical brief’s upper limit (37.4 degrees Celsius for the stability range, with hyperthermia above 37.5) and the European standard’s 37.5 differ by a fraction of a degree, a reminder that thresholds are conventions. For families, the practical point is to use the thresholds their pediatric provider gives them.

Skin-to-skin contact. Moore and colleagues’ Cochrane review (2016) of early skin-to-skin contact included 46 trials with 3,850 women and infants, all healthy and mostly full term. It found that skin-to-skin mothers were more likely to be breastfeeding at one to four months (average risk ratio 1.24, 95% confidence interval 1.07 to 1.43; moderate-quality evidence). For infants, blood glucose was higher with skin-to-skin contact, but temperature was similar to infants in standard care (mean difference 0.30 degrees Celsius, low-quality evidence with high heterogeneity). The authors noted that no included trial met all criteria for good methodological quality, concluded that evidence supports skin-to-skin contact to promote breastfeeding, and said larger studies are needed to confirm physiological benefit for infants during transition. So WHO’s thermal case for skin-to-skin contact rests heavily on evidence from preterm and low birth weight infants and low-resource settings, while the review of healthy term babies supports it more strongly for feeding than for temperature.

When a reading means “call.” The AAP’s Fever and Your Baby page (updated September 2025) says that a rectal temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher is ordinarily considered a fever, that a rectal reading is the most reliable for infants, that ear thermometers should be avoided under 6 months because the ear canals are too small for an accurate reading, and that for a baby 3 months or younger with such a temperature parents should call the pediatrician immediately, even if the baby has no other signs of illness. It also warns that babies can develop heatstroke if overdressed in hot, humid weather, and that fever should not be confused with heat-related illness.

What this means for doulas

• Explain the why. A small body with a lot of surface area loses heat quickly, and babies cannot shiver or adjust clothing. That reasoning helps parents understand hats, closeness and warm rooms without fear.
• Balance warmth with overheating. WHO and the AAP both flag overheating. A baby who is sweaty, flushed or hot to the touch may be wearing too much. A baby who seems cool and quiet may need more cover or contact. Neither impression replaces a thermometer reading when a parent is worried.
• Support skin-to-skin contact. It helps with feeding and is recommended in the sources above. Remind parents that the baby’s airway and position matter whenever either parent might fall asleep (see the safe sleep article).
• Bathing. WHO’s advice to delay the first bath for at least 24 hours is about hospital and early newborn care. See The Evidence Behind Delayed Newborn Bathing for the nuances.
• Stay in scope. A doula may help a parent take a temperature the way the pediatrician recommended, but the doula does not diagnose a fever or decide how to treat one.

Putting the evidence into practice

1. Ask for the provider’s temperature instructions. Find out where and how the baby’s temperature should be taken (the AAP page describes rectal readings as the most reliable) and the number at which to call.
2. Check the room and the layers. The WHO brief lists direct sun and cool drafts near windows as harmful practices, so keep the baby out of both, and adjust layers up or down based on how the baby is doing, not just a rule.
3. Dry and cover after any wetting. After a diaper change, spit-up or a bath, dry the baby and re-cover promptly.
4. Offer skin-to-skin contact when the family wants it, especially in the first weeks and for calming and feeding.
5. Escalate quickly. A fever reading at or above the threshold in a baby 3 months or younger, a baby who is unusually cold, limp, very sleepy or feeding poorly, or any parent worry about temperature warrants a call to the pediatric provider or emergency services. See Recognizing When a Newborn Needs Medical Evaluation: Essential Red Flags for Postpartum Doulas.

Limits and uncertainty

Most of the evidence on hypothermia comes from preterm, low birth weight or low-resource settings, so its numbers do not translate directly to healthy term babies in a typical home. The Cochrane review of skin-to-skin contact covered healthy babies in trials of small size and mixed quality, and its temperature outcome was low-quality evidence. Published normal-temperature ranges differ slightly, the technical brief concerns inpatient and facility newborn care rather than home care, and its clothing advice (1 to 2 layers more than adults) should not be applied to sleep. This article draws on the full text of the technical brief, the European standard and the AAP page, and the abstract of the Cochrane review. This article does not review evidence comparing home thermometer types, and the AAP page notes that underarm readings may use a lower cutoff for fever than rectal readings, which a clinician should explain to parents.

The bottom line

Newborns lose heat quickly, but they can also overheat, and the right response is attention rather than anxiety: dry them, keep them close, dress them sensibly, keep the room comfortable and call the pediatric provider promptly for fever or an unusually cold, sleepy or unwell baby. A doula’s job is to make those habits easy and to know exactly where clinical judgment takes over.

Birth & Baby University’s For Doulas page brings together its postpartum doula training, recertification and mentorship for doulas who support families through the newborn weeks. Check that any program meets your certifier’s, employer’s or state’s requirements before you enroll.

This article is for professional education. It is not medical, legal or tax advice. Check the standards of your certifying organization and the rules where you work. For concerns about a baby’s health, contact a pediatric provider or emergency services.

Sources and further reading

• Safe and Effective Thermal Protection for Inpatient Care of Newborns (Do No Harm technical brief, hosted by the World Health Organization; PDF dated July 2019). Read the source
• European Standards of Care for Newborn Health. Temperature management in newborn infants. Read the source (read October 2026)
• Moore ER, et al. Early skin-to-skin contact for mothers and their healthy newborn infants. Cochrane Database of Systematic Reviews (2016). Read the source
• American Academy of Pediatrics. How to Keep Your Sleeping Baby Safe: AAP Policy Explained (HealthyChildren.org, updated September 2026). Read the source
• American Academy of Pediatrics. Fever and Your Baby (HealthyChildren.org, last updated September 2025). Read the source

More for professionals: the Professionals Blog.