A baby, especially a newborn, cannot regulate internal temperature as effectively as an adult due to their relatively small body size. Infants have a high surface area-to-volume ratio, causing them to lose heat quickly to the surrounding environment. They also lack the insulating layer of fat and the fully developed nervous system needed to maintain a stable core temperature. This vulnerability means a baby’s temperature can drop rapidly, making monitoring an ongoing part of infant care.
Getting an Accurate Temperature Reading
Determining if a baby’s temperature is truly low requires using the correct technique and equipment. A digital thermometer should be used, and mercury thermometers must be avoided due to safety concerns. For infants younger than three months, the most accurate reading is obtained rectally, measuring the body’s core temperature. The digital rectal thermometer tip should be lubricated and inserted gently, no more than one-half to one inch into the anus.
Forehead (temporal artery) thermometers are the next most accurate option, suitable for infants over three months or for initial screening in younger babies. Armpit (axillary) temperatures are the least accurate but can be used for screening at any age; concerning readings should be confirmed with a rectal or temporal measurement. Ear (tympanic) thermometers are not recommended for newborns or infants under six months old because the small, curved ear canal interferes with the device’s accuracy.
The Threshold for Low Body Temperature
A baby’s normal rectal temperature typically ranges between $97.9^{\circ}\text{F}$ ($36.6^{\circ}\text{C}$) and $100.4^{\circ}\text{F}$ ($38.0^{\circ}\text{C}$). The World Health Organization (WHO) defines neonatal hypothermia as a core body temperature below $97.7^{\circ}\text{F}$ ($36.5^{\circ}\text{C}$). A temperature between $96.8^{\circ}\text{F}$ and $97.5^{\circ}\text{F}$ ($36.0^{\circ}\text{C}$ to $36.4^{\circ}\text{C}$) is referred to as “cold stress,” serving as a warning sign.
Cold stress forces the body to burn energy to generate heat, consuming glucose stores rapidly. This increased metabolic demand can lead to hypoglycemia, or dangerously low blood sugar. If the temperature continues to drop, the baby may enter true hypothermia, defined as a rectal temperature below $95^{\circ}\text{F}$ ($35^{\circ}\text{C}$).
Hypothermia is a serious medical state that impairs the respiratory system, leading to shallow breathing and decreased oxygen saturation. Metabolic changes can also cause metabolic acidosis, disrupting the body’s pH balance. Prolonged low temperatures divert energy away from growth and immune function, increasing the risk of infection and, in severe cases, multi-organ failure.
Why a Baby’s Temperature Might Drop
The most frequent cause is exposure to a cool environment. Newborns lack the ability to shiver, the mechanism adults use to generate heat, making them susceptible to heat loss through radiation, convection, and evaporation. Evaporative heat loss occurs rapidly when a baby’s skin or clothing is wet, such as after a bath or due to a wet diaper.
Environmental factors like cold drafts, air conditioning, or a cold car seat can cause a temperature drop. Insufficient clothing or inadequate swaddling prevents the baby from conserving heat. Premature infants and those with low birth weight are at higher risk because they have less body fat for insulation and a larger skin surface area.
A low temperature can also signal an underlying medical issue, particularly in young infants. Infections like sepsis, a serious bacterial infection of the blood, may cause the temperature to drop instead of rising to a fever. Other physiological causes include hypoglycemia or, in rare cases, an issue with the brain’s temperature-regulating center.
Immediate Actions and Medical Intervention
If a baby’s temperature is low, immediate, gentle rewarming is necessary to prevent further heat loss. The first step is moving the baby to a warmer location and promptly removing any cold or wet clothing. Skin-to-skin contact with a caregiver is a highly effective passive rewarming technique, as the parent’s body heat helps stabilize the infant’s temperature.
The baby should be wrapped snugly in warm blankets, and their head covered with a hat to conserve heat. Warming should focus on the core of the body, such as the chest and groin, and must be done gradually to avoid stressing the infant’s system. The baby’s temperature should be rechecked after a few minutes to monitor for improvement.
Caregivers should seek immediate medical attention if the baby’s rectal temperature is below $97.7^{\circ}\text{F}$ ($36.5^{\circ}\text{C}$). Emergency medical services should be contacted if the temperature is below $95^{\circ}\text{F}$ ($35^{\circ}\text{C}$), if the temperature continues to fall despite rewarming efforts, or if the baby appears lethargic, sluggish, or has pale, cold skin. A health professional will be able to determine if the low temperature is due to simple cold exposure or a more serious underlying infection or metabolic issue.