Your baby’s sweet noggin is undoubtedly cute, but it can also — perhaps surprisingly — clue you in to one aspect of your baby’s health. All it takes is a quick check of the top of your baby’s head.

If you notice a significantly sunken soft spot on top, it could be a sign that your baby isn’t getting enough fluid. 

What is a fontanelle or soft spot?

Your baby has two soft spots, or fontanelles, on his head. The larger of the two is located on the very top of the head. The second, smaller one is located toward the back of the head.

If you gently touch these areas, you’ll notice that they aren’t hard like the rest of your baby’s head. The reason? The fontanelles are spaces between skull bones. Their purpose is to give your little one's head the flexibility it needed to squeeze and mold itself to fit through the birth canal during delivery.

Soft spots serve an additional purpose after birth: They allow for the phenomenal growth your baby’s brain is undergoing in the first year. The smaller, posterior fontanelle fuses together completely by 2 to 3 months. The top (or anterior) fontanelle starts to close at 6 months and will usually fuse together completely between 19 and 24 months.

What is a sunken fontanelle or sunken soft spot?

The anterior fontanelle normally appears flat and firm. Sometimes it can bulge slightly (such as when your baby cries) or even pulse along with his heartbeat. Less often, it can appear to be concave, or sunken.

It’s okay if it curves inward slightly to the touch. But if the soft spot is significantly sunken, it’s usually a sign that your baby is dehydrated and needs fluids immediately.

Signs of a sunken fontanelle or sunken soft spot

If the fontanelle on the top of his head isn’t flat but rather significantly dips inward, it means your baby's fontanelle is sunken.

Causes of a sunken fontanelle or sunken soft spot on baby’s head

Your baby’s fontanelle changes with his state of hydration. A well-hydrated baby will have a fontanelle that is flat and firm. If your baby isn’t getting enough fluids and is dehydrated, his soft spot can start to appear sunken.

What can I do about my baby’s sunken soft spot?

No need to worry if your baby’s fontanelle seems slightly indented. But if your baby has a noticeably sunken soft spot, it’s important that you give him additional fluids as soon as possible. If you’re breastfeeding, nurse more often. If you’re bottle-feeding, add in an additional few bottles. 

When to call the doctor

A significantly sunken fontanelle, along with other signs of dehydration (such as a decreased number of diapers, dark urine, tearless crying and sunken eyes), warrants a call to the doctor right away.

Remember, there’s no need to be overly concerned about your baby’s fontanelle — or even to be overly protective of it — but if you notice that baby’s soft spot appears very sunken, it’s important that you contact your pediatrician right away.