The regulation of body temperature is a complex biological process that newborns and young infants have not fully mastered. Unlike older children and adults, a baby’s body surface area is large relative to its mass, which causes them to lose heat much more quickly to the surrounding environment. This limited ability to maintain a stable core temperature means that a drop in reading is a significant concern for caregivers. Understanding what constitutes a low temperature and how to respond is important.
Establishing the Threshold: What Defines a Low Temperature
The normal body temperature for an infant, when measured rectally, generally falls between 97.7°F and 99.5°F (36.5°C and 37.5°C). A temperature is considered low when it dips below 97.7°F (36.5°C), signaling that the body is struggling to maintain warmth. This initial drop is often called “cold stress,” where the baby must expend extra energy and oxygen to generate heat, which can be metabolically taxing. The clinical definition of hypothermia, a dangerously low body temperature, is a reading below 95.0°F (35.0°C). Mild hypothermia typically ranges from 90°F to 95°F (32°C to 35°C), and demands immediate attention because infants cannot shiver effectively to warm themselves.
Accurate Measurement Techniques
When a low temperature is suspected, obtaining an accurate measurement is paramount, as an incorrect reading can lead to inappropriate action or delayed care. For infants, especially those under three months of age, the rectal method is the most accurate way to determine core body temperature. This method is the established standard because it provides the closest approximation to the body’s internal temperature.
To take a rectal temperature, use a digital thermometer lubricated with petroleum jelly. Gently insert the tip only about half an inch to one inch into the baby’s rectum, or until the tip is no longer visible. Hold the baby still until the thermometer registers its final reading, typically signaled by a beep, then record the result and the measurement method used.
Other measurement sites, such as the axillary (armpit) or temporal artery (forehead), are less reliable, particularly when a low temperature is suspected. Axillary readings are generally at least one degree Fahrenheit lower than rectal readings, which can mask a true temperature drop. Temporal or tympanic (ear) readings can also be affected by ambient temperature or improper placement. While convenient, these alternative methods should not be relied upon for critical decisions concerning a low temperature in a young infant.
Identifying Causes and Implementing Immediate Response
A low temperature is often traced to environmental factors, as infants lack the insulating fat and developed thermoregulation systems of adults. Heat can be lost through evaporation and convection from exposure to a cool room, prolonged undressing, or wet clothing or blankets. Newborns, especially those born prematurely or with a low birth weight, are at a higher risk due to their greater surface-area-to-volume ratio, which accelerates heat loss.
Beyond environmental exposure, a low temperature can signal an underlying medical concern that requires immediate attention. Infections like sepsis or meningitis may cause a drop in body temperature rather than the expected fever response in infants. Low blood sugar, known as hypoglycemia, is another metabolic issue that interferes with the body’s ability to generate and maintain warmth.
If a low temperature is detected, immediate steps must be taken to safely rewarm the baby. The most effective first measure is immediate skin-to-skin contact with a parent or caregiver, which transfers stable body heat directly to the infant. The baby should be dried if wet, moved to a warmer environment, and covered with warm blankets, including a hat to minimize heat loss from the head.
It is important to avoid using direct, intense heat sources like hot water bottles or electric heating pads, as these can cause burns to the baby’s delicate skin. If the temperature remains low despite initial warming efforts, or if concerning symptoms accompany the low temperature, seek emergency medical care immediately. Symptoms that warrant an emergency call include:
- Lethargy
- Poor feeding
- Difficulty breathing
- Pale, blue-tinged skin