Why is the back of my head flat and dent on top? Causes and Solutions

October 1, 2025 •

6 min read

An estimated 50% of infants develop some degree of positional plagiocephaly, or a flat spot on the head, often from constant pressure in one position. For adults asking, 'Why is the back of my head flat and dent on top?', the explanation can range from an uncorrected childhood condition to more complex causes like trauma or underlying medical issues that affect the skull's shape over time.

Quick Summary

A flat back of the head is often from infant positional plagiocephaly, while dents in adults can be due to congenital variations, head trauma, rare bone disorders, or past surgery. A doctor's evaluation is recommended for new or concerning changes to the skull's shape. Treatment depends on the underlying cause and the patient's age.

Key Points

Infant Plagiocephaly: Flat spots are often caused by consistent pressure in one position during infancy and are usually treatable with repositioning or helmet therapy.
Adult Dents: New or worsening dents in adults can result from trauma, rare bone disorders, or post-surgical changes and should be evaluated by a doctor.
Craniosynostosis: A more serious, congenital condition involving premature fusion of skull plates that restricts growth and requires medical intervention, often surgery.
Normal Variation: Many head shape anomalies, especially if present since birth and unchanged, are simply harmless natural variations in anatomy.
When to Seek Help: Consult a healthcare provider for any new or painful dents, or for persistent head shape issues in infants beyond early months, especially if other symptoms are present.

Causes of a Flat Spot on the Back of the Head

A flat spot on the back of the head, particularly noticeable in infants, is most commonly caused by deformational or positional plagiocephaly, also known as 'flat head syndrome'. The human skull is soft and malleable in the early months of life to allow for rapid brain growth and passage through the birth canal. Because infants spend a large amount of time lying on their backs, constant pressure on one area can cause it to flatten. While this is usually a cosmetic concern that doesn't affect brain development, it can become more permanent if not addressed early.

Positional Plagiocephaly (Flat Head Syndrome)

This non-synostotic condition results from repeated external pressure. The Back to Sleep campaign, while crucial for reducing Sudden Infant Death Syndrome (SIDS), has contributed to the rise of this condition. Other contributing factors can include:

Intrauterine Positioning: A tight space in the womb, especially with multiple pregnancies, can put pressure on the fetal skull.
Torticollis: A tightening or shortening of the neck muscles can cause a baby to favor turning their head to one side, increasing pressure on that area.
Prematurity: Premature babies have softer skulls and often spend extended periods in a fixed position in a hospital's neonatal intensive care unit (NICU).
Excessive Use of Carriers: Spending too much time in car seats, swings, and bouncers can also limit head movement and contribute to flattening.

Craniosynostosis

In rarer cases, a flat head is caused by craniosynostosis, a congenital birth defect where one or more of the fibrous joints (sutures) between the skull bones fuse prematurely. This restricts normal head growth and can lead to specific, abnormal skull shapes, which may require surgery to correct. Unlike positional plagiocephaly, the deformity associated with craniosynostosis does not improve with repositioning.

Understanding Dents and Indentations on the Top of the Head

For adults, a dent or indentation in the skull can be caused by a range of factors, from natural variations to serious medical issues. It is important to distinguish between longstanding characteristics and new or changing indentations.

Natural Variations and Genetics

It is normal for there to be variations in the shape of a person's skull. Some people are born with slight bumps, ridges, or indentations due to natural bone structure or how the skull plates formed during infancy. If a dent has been present since birth or early childhood and has not changed, it is likely a harmless congenital variation.

Head Trauma and Injuries

Significant impacts to the head can cause a depressed skull fracture, where a portion of the skull is crushed inward toward the brain, leading to a noticeable dent. These injuries require immediate emergency medical attention. Even milder, older trauma can sometimes leave a lasting soft tissue or bone defect.

Medical Conditions

New or changing dents can sometimes be a sign of an underlying medical condition, though this is rare:

Paget's Disease of Bone: This condition interferes with the body's bone recycling process, leading to abnormal, enlarged, or misshapen bones, including the skull.
Bone Tumors: Both benign and cancerous bone tumors can cause a change in skull shape, including depressions.
Gorham-Stout Syndrome: This very rare 'vanishing bone disease' leads to the progressive loss of bone mass and can cause skull indentations.
Vitamin A Deficiency: A severe, prolonged deficiency can soften bones, which may result in a dent.

Post-Surgical Effects

Some head surgeries, such as a craniectomy performed to relieve pressure on the brain, may temporarily leave an indentation until the removed bone is replaced.

When to Consult a Doctor

If you notice a new or concerning change to the shape of your head, or your child's head, a medical evaluation is recommended. See a healthcare provider immediately if a dent appears after a head injury. You should also seek medical advice for infants if:

The head shape has not improved after a few weeks.
Bulging or unusual indentations appear.
The infant has difficulty moving their head or favors one side.
The soft spot (fontanelle) on the head seems sunken or bulging.

How to Tell the Difference: Plagiocephaly vs. Craniosynostosis


Feature	Positional Plagiocephaly	Craniosynostosis
Cause	External, constant pressure on the soft infant skull.	Premature fusion of one or more cranial sutures.
Symmetry	Head may be asymmetrical, with flattening on one side of the back of the head. Features may seem misaligned.	Can cause a variety of abnormal, specific head shapes depending on which suture is fused.
Feel	Soft spots (fontanelles) remain open and the skull sutures feel normal.	The fused sutures feel like a hard, bony ridge.
Treatment	Non-surgical methods like repositioning, tummy time, and helmet therapy.	Often requires surgical correction to allow for proper brain growth and head shape development.
Prognosis	Usually excellent, especially with early intervention. Often improves as the baby spends more time upright.	Excellent with early and proper surgical treatment, though facial asymmetry may persist in some cases.

Treatment Approaches for Head Shape Issues

Treatment depends on the age of the patient and the underlying cause of the head shape abnormality. For infants, intervention is most effective when their skulls are still pliable.

For positional plagiocephaly:

Repositioning: Changing the baby's sleep and play positions, increasing supervised tummy time, and varying the direction the baby faces in their crib can help redistribute pressure on the skull.
Helmet Therapy: For more moderate or severe cases, a custom-fitted cranial remolding helmet or band can apply gentle pressure to encourage reshaping. This is most effective between 4 and 12 months of age.
Physical Therapy: If torticollis (neck muscle tightness) is a factor, physical therapy can help improve neck mobility and range of motion.

For craniosynostosis, surgery is typically required to separate the fused skull bones and allow the brain to grow properly.

For adults, treatment is determined by the cause of the dent:

Monitoring: If the dent is a natural, harmless variation or a result of old, mild trauma, no treatment may be needed.
Surgery: For specific medical conditions like tumors or depressed skull fractures, surgery may be necessary to correct the bone structure. Small cosmetic imperfections can sometimes be corrected with implants or cranioplasty.
Addressing Underlying Conditions: If a systemic disease like Paget's or a vitamin deficiency is the cause, treatment focuses on managing that condition.

Conclusion

A flat spot on the back of the head and a dent on the top are two different conditions with distinct causes. While a flat head in infants is a common and often harmless condition known as positional plagiocephaly, a new dent in an adult's skull warrants a medical evaluation to rule out underlying issues. Conversely, a long-standing, stable indentation is often just a normal variation in anatomy. In all cases, new or worsening symptoms should prompt a consultation with a healthcare professional to ensure proper diagnosis and treatment. For infants, early intervention is key to achieving the best results.

Preventing Positional Plagiocephaly in Infants

Parents can take several simple steps to prevent or correct mild flattening of a baby's head:

Maximize Tummy Time: Provide plenty of supervised playtime on the tummy when the baby is awake. This strengthens neck and shoulder muscles and relieves pressure on the back of the head.
Vary Sleeping Direction: Alternate the end of the crib where the baby's head rests. Babies often look toward the door or other activity in the room, so this encourages them to turn their heads in different directions.
Alternate Positions: Hold, feed, and carry your baby in different positions, switching sides often. Limit time spent in car seats, swings, and bouncers.
Address Torticollis: If you suspect neck muscle tightness, speak with your pediatrician about stretching exercises or physical therapy.

Consult a Professional

For infants with persistent or severe head shape abnormalities, or for any new or painful dents in an adult's skull, a medical professional is the best source of advice. For information on specific treatments like cranial remolding helmets, reputable sources like the American Association of Neurological Surgeons (AANS) can provide further guidance.

Frequently Asked Questions

Positional plagiocephaly is a common, non-serious condition caused by external pressure on a baby's soft skull. Craniosynostosis is a rare, more serious birth defect where the skull's bones fuse too early, restricting brain growth and often requiring surgery.

For most cases of positional plagiocephaly, a flat spot will not cause problems in adulthood. The main concern is often cosmetic, and the condition generally does not affect brain growth or development.

You should see a doctor if a dent is new, painful, changing in size, or appears after a head injury. While often harmless, these can sometimes indicate serious conditions like a depressed skull fracture or a bone tumor.

Treatment for infants with positional plagiocephaly can involve simple repositioning techniques, increasing tummy time, and using a cranial remolding helmet for more severe cases. A doctor might also recommend physical therapy if neck muscle tightness is a factor.

It is rare, but certain bone cancers or cancers that have spread to the bone can sometimes cause depressions in the skull. This is why any new or unexplained dent should be evaluated by a doctor.

If a flat head from positional plagiocephaly was not fully corrected in infancy, the head shape will likely remain asymmetrical into adulthood. Since the skull bones are hardened, repositioning techniques are no longer effective, and cosmetic surgery is the only treatment option.

Yes, it can. Many people have minor congenital variations in their skull shape that are entirely normal and harmless. A long-standing, non-painful indentation that hasn't changed is often a normal part of a person's unique bone structure.