The system that controls body temperature is not well developed in a newborn. Call your baby's doctor immediately if your baby is younger than 3 months old and has a rectal temperature of 100.4°F (38°C) or higher.
A fever is common when an adult has an infection. In newborns, fever may or may not occur with an infection. A newborn may actually have a low body temperature with an infection. He or she may also have changes in activity, feeding, or skin color.
While it is important to keep a baby from becoming chilled, a baby can also become overheated with many layers of clothing and blankets. An overheated baby may have a hot, red, or flushed face, and may be restless. To avoid overheating:
Keep your baby away from any source of heat. For example, a room heater, fireplace, heating vent, or direct sunlight.
Keep your home at about 72°F to 75°F.
Dress your baby comfortably. He or she doesn't need more clothing than you do.
Cars can get very hot. Be extra careful when dressing your baby to go for a car ride.
Newborns may not take in enough breast milk or formula. This may cause an increase in body temperature. If you think your baby isn't eating enough, either breast milk or formula, call his or her health care provider. Make sure you know how to check your baby's temperature and have a thermometer. Call your baby's health care provider right away if he or she has a fever.