Is 38.4 Celsius dangerous for an 6 month old baby?

If concerned, you should consult a physician. However fevers up to 39 Celsius are common and normal in infants, and are not dangerous. Higher fevers can be brought down with Advil or Tylenol, as recommended by a doctor. Do not give aspirin to babies.

The usual advice is to "watch the baby, not the thermometer". Look for signs of lethargy, irritability, or seizure when deciding whether to seek medical attention.