By Emily Brown, MPH 

 Medically reviewed by Daniel Combs, MD

Babies are born with soft spots (fontanels) on their heads where the skull bones haven’t fully come together. These small gaps are made of connective tissue. They allow the brain to grow and develop before the skull bones fuse together. 

There are two main soft spots, one on top of the head and the other at the back of the head. Each has a distinct shape and size. Certain conditions can change the appearance of the soft spots, which may indicate abnormalities in development. However, a change in appearance can be temporary and normal. 

This article looks at the anatomy and function of baby soft spots and what to look out for as they change and close.

Anatomy

Soft spots on a baby’s head are areas where the platelike bones of the skull have not fully fused together. The spaces between the bones are made of a strong fibrous material—known as connective tissue—which is somewhat soft to the touch, therefore giving them the name “soft spot.” As the brain and skull develop, the skull bones come together, and the soft spots go away. 

There are six soft spots present during infancy.1 The two most notable ones are:

• The anterior fontanel: This is the commonly known soft spot. It is located on top of the head, is diamond-shaped, and measures just under a half-inch to a little over an inch (about 1 centimeter to 3 centimeters) at birth. It is formed by the spaces between the bones at the front of the skull and those on the sides. 

• The posterior fontanel: This is at the back of the head and is triangular in shape. It is lesser-known perhaps due to its smaller size, which is about one-quarter inch (5 millimeters to 7 millimeters) at birth. This soft spot is in between the bones on the sides of the head and the one at the back. 

Soft Spots Come in Different Sizes

As with bodies, individual soft spots come in different sizes, so it is important to note that not all soft spots are the same.

In fact, research has shown that there are racial and ethnic differences in the sizes of soft spots.2

Function

The soft spots serve two purposes:

• Fitting through the birth canal: The connective tissue-filled gaps between the skull bones allow the bones to shift so that the baby’s head can fit through the birth canal without damaging the brain. 

• Allowing the brain to grow: The rapid growth and development of the brain is a normal part of infancy, and without these gaps between the skull bones, the brain wouldn’t be able to grow fully.

As a baby matures, the bone-making cells in their skull create new layers of bone that spread to the outer portion of the skull bones while also strengthening the inner framework of the bones.

Monitoring the age at which the soft spots go away (when the skull bones fuse together) serves as a marker of development.

When Do Soft Spots Close?

The following are guidelines regarding closure of the two main soft spots:

• The larger, anterior one is usually the second to close, and this occurs between nine months and 18 months after birth.

• The posterior soft spot usually closes around six weeks to eight weeks after birth.3

Associated Conditions

The structure of a baby’s soft spot offers some information about a baby’s health. The best way to evaluate the appearance of a baby’s soft spot is by propping the baby upright while they are sleeping or feeding. A noticeable change in appearance or size may indicate a medical condition. 

For example:

• A sunken soft spot may mean that a baby is dehydrated.3 Other signs of dehydration include dry mucus, crying without tears, and decreased urination (such as a lack of wet diapers).

• A bulging anterior soft spot may mean that the baby has increased intracranial pressure, which, in turn, may indicate conditions such as hydrocephalus (a buildup of fluid in the brain), hypoxemia (low oxygen levels), meningitis (inflammation of the membranes covering the brain and spinal cord), trauma, or hemorrhage (bleeding).1

However, it is important to note that intense crying can cause a bulging soft spot in a healthy baby.4 The question to ask here is, does it linger? If a soft spot is still bulging or swollen after a baby has calmed down and is resting, this may be something to monitor and talk to your pediatrician about.

Another thing to know is that soft spots that close earlier or later than expected may indicate a developmental abnormality. For example:

• A posterior soft spot that lingers more than 8 weeks may indicate underlying hydrocephalus or congenital hypothyroidism (an underactive thyroid).

• Skeletal disorders, such as those arising from conditions like rickets, and genetic disorders, including Down syndrome, are also sometimes responsible for delayed closure of the soft spots.3

These conditions can be assessed through physical exams and lab tests. So, if you’re concerned that your baby’s soft spots are closing too early or too late—keeping in mind that “normal” closure is on a range—reach out to your pediatrician.

Caring for the Soft Spots

Caring for soft spots is not complicated. In general, leaving them alone is best. However, there are some signs to look out for to help monitor healthy growth and development.

Here are some facts to know:

• The soft spots should look flat against the baby's head and not like they are bulging or sunken in.

• If you run your fingers over the top of a baby’s head, the anterior soft spot should feel soft and flat. It also should have a slight downward curve to it.

• In addition to crying, lying down and vomiting may also cause a baby’s anterior soft spot to swell and look like it’s bulging. As long as it goes down when the baby is upright and calmed down, it usually is fine.

• The soft spot sometimes pulsates in rhythm with the baby's heartbeat, which is normal.

While soft spots may seem vulnerable, the connective tissue they are made of is strong enough to protect the brain. It is safe to gently touch a baby’s head (even on the soft spots), put a hat or headband on their head, and wash or brush their hair.

Concerns

Soft spots are normal and tell us that the brain has room to grow and develop. The size, shape, and appearance of a baby’s soft spots are like points on a plot of development. By knowing what is expected and when, you can better understand your baby's development.

Remember, there is a general range for size and closure of soft spots. However, if you are concerned about the appearance of your baby's soft spots or their premature or delayed closure, ask your pediatrician, who will examine the soft spots during routine child visits. Your doctor can help rule out other causes and provide guidance on treatment, if needed.

Frequently Asked Questions

When do a baby's soft spots close?

Generally speaking, the anterior soft spot (the one on top of the head) closes when the baby is between 9 months old and 18 months old, while the posterior soft spot (at the back of the head) closes sooner, between six weeks and eight weeks after birth.

Why do babies have soft spots?

Babies have soft spots for two main reasons. The first is to provide flexibility, allowing the head to fit through the birth canal. The second reason is to give the brain, which grows considerably in infancy, room to expand.

What happens if my baby's soft spot closes early?

Remember, there is no hard and fast date on when your baby’s soft spots should close. Rather, it is a range. But if you notice that one of your baby’s soft spots is closing before the range, this could be a cause for concern as it can impact brain development. It is best to speak to your pediatrician if it seems the soft spot is closing too early.

When should you worry about your baby's soft spot?

If your baby’s fontanel appears sunken, swollen, or bulging, or if it disappears sooner than expected, see your doctor. These can be signs of dehydration, a recent fall, fluid buildup, or something else concerning.

Sources

Lipsett B, Reddy V, Steanson K. Anatomy, head and neck, fontanelles. StatPearls Publishing.

Boran P, Oğuz F, Furman A, Sakarya S. Evaluation of fontanel size variation and closure time in children followed up from birth to 24 months. Journal of Neurosurgery: Pediatrics. 2018;22(3):323-329. doi:10.3171/2018.3.peds17675

Esmaeili M, Esmaeili M, Ghane Sharbaf F, Bokharaie S. Fontanel size from birth to 24 months of age in Iranian children. Iran J Child Neurol. 2015;9(4):15-23.

MedlinePlus. Fontanelles.

By Emily Brown, MPH
Emily is a health communication consultant, writer, and editor at EVR Creative, specializing in public health research and health promotion. With a scientific background and a passion for creative writing, her work illustrates the value of evidence-based information and creativity in advancing public health.