The anxiety a parent feels when an infant’s temperature is low is understandable, as babies have an underdeveloped ability to regulate their body heat. Unlike older children and adults, newborns lose heat rapidly. A low temperature can be due to simple environmental exposure or signal a serious underlying medical problem. Understanding this difference is important, as while minor dips can be resolved with simple warming measures, others require immediate medical attention.
Defining Low Temperature in Infants
A healthy, full-term baby maintains a core body temperature between 97.7°F (36.5°C) and 99.5°F (37.5°C). A low body temperature, or hypothermia, is defined as below 97.7°F (36.5°C). This mild dip is often called “cold stress” and prompts the baby’s body to use energy to warm up.
The most accurate way to measure an infant’s core temperature, especially in newborns under three months, is with a rectal thermometer. Other methods, such as axillary (armpit) or temporal artery (forehead) readings, are less precise. A persistent low reading, particularly one below 96.8°F (36.0°C), warrants immediate attention and indicates true hypothermia.
Common Environmental Factors
Infants are highly susceptible to environmental changes because they possess a large surface area relative to their small body mass, causing them to lose heat four times faster than adults. This heat loss occurs through four main physical mechanisms influenced by the baby’s immediate surroundings.
Evaporation is a rapid cause of heat loss, occurring when moisture on the skin converts to vapor. This happens if a baby is not dried thoroughly after a bath or if a wet diaper is left unchanged, causing a sudden temperature drop. Convection involves heat loss to cooler, moving air, such as drafts from an open window or a vent. Positioning the baby near a draft can cause a temperature drop even in a warm room.
Radiation is the transfer of heat from the baby’s warm body to cooler solid objects nearby, even without direct contact. Placing a bassinet next to a cold exterior wall or windowpane causes the baby to radiate heat away. Conduction is direct heat transfer to a cooler surface, such as an unheated changing table, a cold scale, or a cool mattress. These environmental factors are the most common causes of low temperature and are often the easiest to correct.
Physiological and Illness-Related Causes
When environmental factors are ruled out, a low temperature may signal an underlying medical issue or difficulty with thermoregulation. Newborns, particularly those born prematurely, have an immature thermoregulatory system that makes maintaining a stable temperature difficult. They have limited insulating subcutaneous fat and insufficient reserves of brown fat, the specialized tissue used to generate heat metabolically.
One concerning internal cause is the relationship between low body temperature and low blood sugar, known as hypoglycemia. When a baby gets cold, the body burns limited glycogen stores to produce heat, rapidly depleting glucose in the bloodstream. The resulting hypoglycemia starves the body of the energy required for heat generation, which further worsens the hypothermia.
A low temperature can also be the initial sign of a serious infection, such as sepsis, especially in a young infant. Unlike older children who respond to infection with a fever, an infant’s immature immune system may present with a low temperature, indicating the body is struggling to mount a response. Severe symptoms, such as lethargy, poor feeding, or difficulty breathing, indicate the low temperature is linked to a serious medical condition.
Immediate Actions and When to Call a Doctor
If a low temperature is detected, immediate rewarming efforts are necessary. The most effective initial step is skin-to-skin contact, where the baby is placed bare-chested on the parent’s chest and covered with a blanket. This method utilizes the parent’s stable body temperature to gently warm the infant.
The baby should be wrapped in warm, dry clothing, including a hat and socks, and given a fresh diaper if the previous one was wet. Offering a feeding is also important, as the energy from breast milk or formula can help counteract potential hypoglycemia. The baby’s temperature should be re-checked after 30 minutes to confirm the warming efforts are successful.
Immediate medical attention is needed if the baby’s temperature is below 96.8°F (36.0°C) and does not begin to rise after 30 minutes of warming efforts. Any low temperature accompanied by red flag symptoms warrants an emergency call. These signs include sluggishness, difficulty waking, a weak cry, pale or mottled skin, or labored breathing.