It's normal for it to pulse gently and to dip slightly when a baby is upright. A noticeably sunken fontanelle can be a sign of dehydration, while a tense, bulging one (especially with fever or unusual sleepiness) needs urgent medical review.
Glossary
Fontanelle (soft spot)
A fontanelle is one of the soft gaps between the bones of a baby's skull that lets the head grow — the larger one on top usually closes between about 12 and 18 months.
Related guides
Spotting dehydration
A calm, practical guide to noticing when your baby needs more fluids — and the urgent signs that mean it's time to call for help.
When to call the doctor
A calm, plain-language map of the symptoms that mean wait-and-watch, ring today, or go now — so you can trust your gut without second-guessing.
General information, not medical advice. For concerns about your child, talk with your doctor or child-health nurse.