Intense crying can cause a temporary increase in a baby’s body temperature, leading to a higher reading on a thermometer. This warmth is generally not a true fever, which is a controlled immune response to fight infection. Understanding the difference between exertion-related warmth and an illness-related temperature elevation is important for accurately assessing a baby’s health.
How Crying Generates Body Heat
Intense crying is a significant physical activity for an infant, similar to a short burst of exercise. The effort requires the forceful contraction of multiple muscle groups, including the chest, diaphragm, throat, and face. This muscle exertion increases the body’s metabolic rate, which is the speed at which the body converts stored energy into work.
Heat is a natural byproduct of this metabolic process. When a baby cries vigorously, the sudden increase in muscle activity generates extra heat, causing the body’s temperature to rise temporarily.
The Expected Range of Temperature Increase
The temperature elevation caused by crying is small and is not considered a true fever. The increase is usually less than one degree Fahrenheit (or half a degree Celsius) above the baby’s normal baseline temperature. This rise is a physiological response to physical effort, not a change in the body’s internal temperature set point.
This small rise is also short-lived because the body regulates its temperature through mechanisms like sweating or increased blood flow to the skin. Once the baby calms down and the physical exertion stops, the temperature usually returns to the normal range quickly. If an elevated temperature is suspected after crying, wait 20 to 30 minutes for the baby to rest and cool down before taking a measurement.
The method of measurement affects the reading. Rectal temperature is the most accurate representation of a baby’s core temperature. Surface measurements, such as those taken under the arm (axillary), are less reliable and can be influenced by external factors like crying.
Knowing When to Be Concerned
A true fever in infants is medically defined as a rectal temperature of 100.4°F (38°C) or higher. The warmth caused by crying is not indicative of illness, but because crying can mask a true fever, parents must use caution. If a temperature reading is elevated immediately after a crying spell, calm the baby, remove excess clothing, and wait 20 to 30 minutes before re-taking the temperature.
If the second reading is still 100.4°F (38°C) or higher, it should be treated as a fever. For infants less than three months old, a rectal temperature at or above this threshold requires immediate contact with a pediatrician or seeking emergency medical attention. For older infants, a sustained fever still warrants a call to the doctor, particularly if the baby is inconsolable, difficult to wake, or shows other signs of distress like reduced feeding or decreased wet diapers.