What is the softest spot on the head?

September 23, 2025 •

3 min read

Every human is born with multiple unfused skull bones, leading to soft spots that are a vital part of early development. For infants, these areas are known as fontanelles, while in adults, the concept of a "softest spot" refers to specific, weaker anatomical regions that are more vulnerable to injury. Understanding these differences is key to proper care and safety throughout a person's life.

Quick Summary

In infants, the softest spot on the head is the anterior fontanelle, a diamond-shaped gap at the top where skull bones have not yet fused, allowing for brain growth and birth canal passage. For adults, no soft spots exist under normal conditions, but the pterion, a junction of four bones near the temple, represents the thinnest and weakest area of the skull.

Key Points

Infant's Softest Spot: The anterior fontanelle, located on the top of a baby's head, is the most prominent soft spot, enabling safe passage through the birth canal and rapid brain growth.
Adult's Weakest Spot: The pterion, found on the side of the head near the temple, is the thinnest and weakest part of the adult skull, and an impact here can be particularly dangerous.
Fontanelle Closure: The posterior fontanelle at the back of a baby's head closes first, usually within the first 2-3 months, while the larger anterior fontanelle closes between 9 and 18 months of age.
Abnormal Soft Spot in Adults: An adult with a soft spot should seek medical attention, as it is not normal and could indicate an underlying medical issue, past injury, or congenital disorder.
Cranial Protection: While a baby's soft spots are covered by a tough membrane, an adult's skull requires protection at its weakest points, especially during activities with a risk of head trauma.
Indicator of Health: The appearance of a fontanelle can signal health concerns in infants; for instance, a sunken fontanelle may indicate dehydration.

Unraveling the 'Softest Spot' Myth for Infants and Adults

Most people's understanding of a "soft spot" on the head comes from newborns, who famously have these areas to accommodate a developing brain and facilitate birth. However, the anatomy of the skull changes dramatically from infancy to adulthood. This comprehensive guide will explore the truth about the softest parts of the head, distinguishing between the crucial developmental features of a baby's skull and the areas of vulnerability in an adult.

The Infant's Soft Spots: Fontanelles

Newborns have fontanelles, or soft spots, where cranial bones haven't yet closed, allowing the skull to mold during birth and the brain to grow rapidly. These spots are covered by a fibrous membrane and can indicate health status to pediatricians.

The Two Most Important Fontanelles

Anterior Fontanelle: The largest, diamond-shaped soft spot on the top of the head. It typically closes between 9 and 18 months.
Posterior Fontanelle: A smaller, triangular spot at the back of the head. It usually closes within the first 2-3 months.

The Adult Skull: No True Soft Spots

By about 18-24 months, infant fontanelles close and fuse. Adults typically have a solid skull, and any soft spot is abnormal, potentially indicating a medical issue, injury, or congenital condition.

The Skull's Weakest Anatomical Point: The Pterion

The adult skull is not uniformly thick. The weakest point is the pterion, an H-shaped area behind the temple.

Anatomy of the Pterion: This is where the frontal, parietal, sphenoid, and temporal bones meet. The middle meningeal artery is located directly beneath it.

Risk of Injury: A blow to the pterion can cause a fracture and rupture the underlying artery, leading to a dangerous epidural hematoma (blood between the skull and brain membrane).

Comparing Cranial Vulnerability: Infant vs. Adult


Feature	Infant Skull	Adult Skull
"Soft Spot"	Multiple fontanelles (anterior and posterior)	None normally present; a soft spot is a medical anomaly
Protective Layer	Covered by tough, fibrous membrane; skull plates are not fused	Bones are fully fused and ossified for maximum protection
Purpose	Accommodates rapid brain growth and enables safe passage during birth	Provides a rigid, protective casing for the fully grown brain
Point of Weakness	The fontanelles themselves, though protected, are not fully enclosed by bone	The pterion, located near the temple, is the thinnest point
Response to Pressure	Can bulge with intracranial pressure or sink with dehydration	A fracture at the pterion can cause a dangerous arterial rupture

What to Do in Case of Head Injury

Any head trauma requires monitoring. Seek immediate medical advice if an infant's soft spot bulges or if an adult shows neurological symptoms after a head injury.

Proper Care and Protection

Gentle handling is fine for infants, as the fontanelle membrane is resilient. Avoid impacts during play. Adults should be aware of the pterion's vulnerability, especially in contact sports, and use safety gear like helmets.

Disclaimer: The information provided in this article is for general knowledge and informational purposes only, and does not constitute medical advice. For specific medical questions or concerns, please consult a qualified healthcare professional. You can find more information about skull anatomy and health on the National Institutes of Health (NIH) website.

Conclusion

Infant soft spots are normal developmental features. Adults lack natural soft spots, but areas like the pterion represent vulnerabilities. Understanding these distinctions helps ensure proper care and appropriate responses to head trauma in all age groups.

Frequently Asked Questions

Under normal circumstances, adults do not have soft spots on their heads, as the skull bones have fully fused. Any perceived soft area is abnormal and warrants medical evaluation to determine the cause.

Babies have soft spots, known as fontanelles, for two primary reasons: to allow their skull to compress during birth for easier passage through the birth canal and to accommodate the rapid growth of their brain during infancy.

The smaller posterior fontanelle at the back of the head typically closes first, within 2 to 3 months. The larger anterior fontanelle on top of the head takes longer, usually closing between 9 and 18 months of age.

Gently touching or washing a baby's fontanelle is safe, as it is protected by a thick, durable membrane. However, excessive pressure or a hard impact should be avoided.

The pterion, a junction of four bones located on the side of the head behind the temple, is the weakest part of the adult skull. A blow to this area can be particularly dangerous due to the underlying middle meningeal artery.

A bulging fontanelle could indicate increased pressure within the skull, which may be caused by conditions like hydrocephalus (fluid buildup), infection (meningitis), or a hemorrhage. This requires immediate medical attention.

Causes of a soft spot in an adult can include genetic disorders that prevent proper bone fusion (e.g., craniosynostosis), previous trauma, or certain medical conditions such as hydrocephalus that can affect bone integrity.