An infant's skull has six main bones and is held together by tissues called sutures. A fontanelle is a small separation between the sutures. These six openings are commonly referred to as soft spots. Soft spots are absolutely normal and allow the bones in the head to overlap during delivery. They also allow space for your baby's brain to grow and develop.
A bulging fontanelle is a medical emergency. This bulging can be caused by fluid in the brain (hydrocephalus); inflammation of the membranes surrounding the brain (meningitis, usually caused by a viral or bacterial infection); inflammation of the brain (encephalitis, mainly caused by viral infection); and shaken baby syndrome (brain injury from violent shaking).
A noticeable inward curve is known as a sunken fontanelle. Several conditions can cause a sunken fontanelle, including dehydration, failure to thrive, a severe form of malnutrition called Kwashiorkor, toxic megacolon (a rare complication of inflammatory bowel syndrome), and diabetes insipidus (when the kidneys can't conserve water when filtering blood).
Babies are usually born with six fontanelles. They are in different places around the skull and close at different times throughout childhood. The posterior fontanelle usually closes first, followed by the sphenoidal fontanelles, mastoid fontanelles, and anterior fontanelle.
The posterior fontanelle is on the upper, rear part of the baby's head. This fontanelle is at the intersection of three different bones. The posterior fontanelle generally closes between 6 weeks and 3 months after birth. It is the first to close.
There are two sphenoid fontanelles on either side of the baby's head near their temple. These fontanelles typically close by the time your baby is six months old.
These smaller gaps, known as the mastoid fontanelles, are on both sides of your baby's skull just behind their ears. These fontanelles will close between 6 and 18 months.
The anterior fontanelle is the largest soft spot. It is in the upper, front portion of your baby's head at the junction of three different sutures. The anterior fontanelle generally closes between 18 and 36 months of age. It is the last to close.
Keep in mind that these closing estimates are averages. Every baby is different!