Infants are uniquely susceptible to fluctuations in environmental temperature because their body’s heat regulation system is still developing. They lose heat to their surroundings much faster than adults. Understanding the threshold for a dangerously low temperature is important for a caregiver, as a significant drop can tax a baby’s metabolism. This guide provides the necessary information to identify, measure, and address a low body temperature in an infant.
Understanding Normal Body Temperature in Infants
The core body temperature of a healthy infant is relatively stable, but the reading depends entirely on the method used. When measured rectally, which is the most accurate method for young babies, the normal range is typically between 97.9°F and 100.2°F (36.6°C and 37.9°C). A rectal temperature may naturally be as low as 96.8°F (36°C) in the early morning for some infants.
The armpit, or axillary, temperature is often used for screening, but this method provides a reading that is generally about one degree Fahrenheit lower than the rectal measurement. Daily fluctuations occur naturally, with temperatures typically being lower in the morning and slightly higher in the late afternoon or evening. Establishing a baseline for a healthy baby can help a parent or caregiver recognize when a reading falls outside that individual’s normal range.
Defining Low Body Temperature and Hypothermia
A temperature that falls below the normal range is a cause for concern, but the specific threshold depends on the medical context. The World Health Organization (WHO) defines a low or unstable temperature in a newborn as anything below 97.7°F (36.5°C). This range, often referred to as “cold stress,” signals that the baby is struggling to maintain their temperature and requires immediate attention to prevent a further drop.
The medical condition known as hypothermia occurs when the core body temperature drops below 95.0°F (35.0°C). Hypothermia is classified into stages based on temperature severity. Mild hypothermia is defined as a temperature between 95.0°F and 89.6°F (35.0°C and 32.0°C).
A temperature between 89.6°F and 82.4°F (32.0°C and 28.0°C) is considered moderate hypothermia, and anything below 82.4°F (28.0°C) is classified as severe. A temperature drop to 95.0°F (35.0°C) or lower requires prompt medical intervention.
Accurate Methods for Taking a Baby’s Temperature
For infants under one year old, a digital rectal thermometer provides the most reliable and accurate measurement of core body temperature. When a low temperature is suspected, this method offers a definitive reading. The thermometer tip should be inserted gently no more than one inch into the rectum until the device beeps.
Axillary or armpit temperature is a convenient method for screening, but it is less accurate than a rectal reading. For this method, the thermometer tip must be placed directly in the center of the armpit and the baby’s arm held gently against their side until the reading is complete. Temporal artery (forehead) and tympanic (ear) thermometers are generally not recommended for very young infants because they can be unreliable due to technique or the small size of the infant’s ear canal.
First Steps When a Baby’s Temperature is Low
When a low temperature is detected, immediate and non-invasive rewarming measures should be taken while observing the baby’s behavior. The most effective initial technique is skin-to-skin contact, where the baby, wearing only a diaper, is placed directly on the parent’s bare chest and covered with a blanket. This method utilizes the caregiver’s stable body heat to gently warm the infant.
Immediate Warming Steps
Moving the baby to a warmer room and ensuring they are dry are important first steps, especially if the low temperature was caused by a cold environment or wet clothing. Dress the baby in an extra layer of clothing and a hat, as heat is lost through the head.
When to Seek Medical Attention
If the rectal temperature remains below 97.7°F (36.5°C) after initial warming attempts, or if the baby shows signs of lethargy or poor feeding, contact a pediatrician immediately. Seek emergency medical care if the temperature is 95.0°F (35.0°C) or lower, or if the baby shows symptoms like sluggishness, pale skin, or difficulty breathing.
Common Reasons for Temperature Drops
Infants are physiologically predisposed to losing heat rapidly due to their body composition and size. They have a large surface area relative to their body weight, which means heat escapes quickly into the surrounding air. Furthermore, newborns have less insulating subcutaneous fat and thinner skin compared to older children and adults.
A major factor is the infant’s inability to shiver, which is the primary way adults generate heat through muscle movement. Instead, babies rely on non-shivering thermogenesis, using specialized brown adipose tissue (brown fat) to produce heat. Common external causes for a temperature drop include being undressed for a bath, exposure to a cold room or draft, or being wet for too long. Illness, particularly infection, can also manifest as hypothermia rather than fever in a young baby.