Since newborns can't regulate their body temperature, overheating can be dangerous. Here are a few signs to look out for if you're concerned your little one is too hot: Skin which is red, flushed, and hot A very fast heartbeat, and quick breaths Being overly restless, or lethargic Having trouble sleeping Being sick, or developing a heat rash Having a rectal temperature that exceeds 100.4 degrees Fahrenheit (38 degrees Celsius) Always contact a pediatrician or other healthcare professional if you have any concerns.