When Do Fontanelles Close?

If you’re preparing for the birth of a new baby, the chances are you’ve probably come across the term ‘baby soft spot’ before. It’s hard to believe, but these spots actually exist to make birth easier for you! Today, we have measures like gas and air, but these evolutionary features are there to help your baby move through the birth canal during a vaginal birth.

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How the fontanelles work

Fontanelles are found on your baby’s skull. You may have heard that young children have more bones than adults – this is because they fuse together as your child grows up. [1]

The same applies on your baby’s head. A baby skull is actually made up of several major bones that have not yet fused together. The ‘gaps’ in these bones are identified by what’s known as ‘suture lines’ and within these lines, we have ‘fontanelles’ or ‘soft spots.’

Babies have fontanelles for two main reasons:

• To protect your baby’s brain as he or she passes through the narrow birth canal
• To allow your baby’s skull to grow in line with their brain development, which expands rapidly between infancy and the first two years.

While we’ve all heard of the ‘soft spot’ on top of a baby’s head, there are actually six fontanelles. The main two are known as the ‘anterior fontanelle’ (the soft spot on top of your baby’s head) and the ‘posterior fontanelle’ (a small opening at the back of the baby’s skull).

Other examples of baby soft spots

The other lesser known fontanelles on a baby’s head are:

1. The sphenoid fontanelle – there are two of these, found on either side of the head near the temple.
2. The mastoid fontanelle – there are also two of these, found on either side of the skull behind your baby’s ears.

How long do babies have a soft spot on their head?

You may be feeling very anxious about handling your baby in their early years, but there is no need to worry. The good news is that fontanelles don’t last forever – so you may not always be in ‘delicate china’ mode!

So, when do babies’ soft spots go away? In truth, it depends on the fontanelle, and the individual baby.

When does posterior fontanelle close?

The posterior fontanelle is typically the first soft spot to close. This happens as early as six weeks after your baby’s birth, but can take up to three months.

Sphenoid fontanelles come next, and are usually closed by the time your baby hits six months. The mastoid fontanelle can take far longer, closing anywhere between six and 18 months.

The anterior fontanelle, otherwise known as the main soft spot on top of the baby’s head, is the last one to go, closing anywhere between 18 and 36 months.

What happens if a fontanelle doesn't close?

Remember, fontanelle closure is different for everybody, and the above figures are based on averages. In some cases, however, a late fontanelle closure could be a sign of something more serious, such as congenital hypothyroidism. This may be accompanied by other symptoms like dry skin or constipation, so always ask your doctor if you’re not sure. [2]

When do fontanelles close late?

Some other potential warning signs for your baby’s soft spot could be swelling or bulging. Contact your doctor if you notice any of the following symptoms:

• A sunken soft spot: This is often a sign of dehydration in infants. You might notice this if your baby has recently been sick and is not getting enough fluids. [3]
• A swollen soft spot: If your baby has had a fall and is vomiting with signs of a swollen soft spot, seek medical advice immediately. [4]
• A bulging soft spot: Bulging could indicate internal bleeding, so get emergency care immediately, particularly if your baby is vomiting or especially fatigued. [5]
• A ‘quiet fontanelle’: This is when a soft spot disappears sooner than expected, and is usually not a cause for concern. However, if the fontanelles only close on one side, it could be a sign of craniosynostosis, so always ask your doctor. [6]

What happens if you touch the soft spot on a baby's head?

It’s completely understandable for you to feel like you’re treading on eggshells when carrying a new baby. But don’t worry – your baby’s soft spots actually contain tough membranes, which protect the soft tissue and brain underneath.

This means you can carry out normal motherly tasks when looking after your baby, such as touching their hair, washing their hair, combing hair, and applying headbands, and even letting other children hold the baby.

What happens if you accidentally hit baby's soft spot?

It’s perfectly normal for accidents to happen, particularly to new mothers, so don’t panic. If your child is acting normally, including crying, then it’s unlikely you have caused them harm. If you’re concerned about serious head trauma, look for warning signs such as:

• Inability to stop crying
• Reluctance to feed
• Vomiting or seizures
• Discharge or blood from the ears and nose
• Trouble waking up after a nap

Always seek medical attention if you’re not sure. Your doctor will appreciate you making the call, and they will be used to it!

Remember, every child is different and will experience fontanelle closure at different times. You may notice occasional bulging, which can move around as your child adjusts or drinks more fluids. The ‘fontaine’ (meaning ‘little spring’ in French) is an essential part of your baby’s brain development – and you may miss those squidgy bits when they’re gone. Just like their tubby little thighs, embrace them while you can!