Perhaps you have already noticed a soft spot on your baby’s head? Perhaps you also felt a moment of panic, wondering why this little hole was there and what it could be!
It is actually an opening in the skull that allows it to move as it grows!
There are two fontanelles on a baby’s head:
- one on the top of the head, called the anterior fontanelle, which is diamond-shaped;
- the other, called the posterior fontanelle, which is located further back on the skull and is smaller and triangular in shape.
These two openings are essential to allow the bones of the baby’s head to overlap during birth, but also to allow the skull to move and expand as your baby’s brain develops. These softer parts of the skull are fragile, but there is nothing to worry about with normal everyday movements, so don’t worry!
The posterior fontanelle takes about 4 months to close in most babies, while the anterior fontanelle is completely closed by 24 months in 96% of babies.
In very young babies, you may sometimes notice a depressed fontanelle, hollowed out in the bone opening surrounding the membrane, which may indicate dehydration. Paradoxically, the fontanelle membrane may also be bulging or swollen. This temporary swelling can be noticed when the baby is exerting themselves (e.g., crying loudly, vomiting, or coughing). However, this observation is also important to consider and should be addressed to your doctor for evaluation if the swelling seems to persist.
Marie Fortier
The baby specialist
Article updated: April 2025.
References:
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Journal de l’association médicale canadienne. (2024). Bombement de la fontanelle chez une enfant fiévreuse de 9 mois. Repéré le 2 avril 2025 à https://pmc.ncbi.nlm.nih.gov/articles/PMC11498334
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American family physician. (2023). La fontanelle anormale. Repéré le 2 avril 2025 à https://www.aafp.org/pubs/afp/issues/2003/0615/p2547.html
