The occipital crest is a low ridge of bone running down the midline of the back of the skull, stretching from the external occipital protuberance (the bump you can feel at the base of the back of your head) toward the foramen magnum (the opening where the spinal cord exits the skull). It serves as an anchor point for muscles and ligaments that hold your head upright, and it varies considerably in size from person to person. The crest and the bump above it gained unexpected public attention around 2018, when researchers proposed that young people were growing enlarged bony spurs there because of smartphone use, though that claim has turned out to be far more complicated than the headlines suggested.
Where It Sits and What Attaches to It
The external occipital crest is part of a system of ridges on the outer surface of the occipital bone, the plate-like bone that forms the lower back of the skull. At the top of this system sits the external occipital protuberance, often abbreviated EOP. Radiating outward from the EOP are the superior nuchal lines, curved ridges that sweep toward each ear. Below those run the inferior nuchal lines. The external occipital crest itself descends vertically from the EOP, giving the whole arrangement the look of a rough cross or anchor shape when viewed from behind.
These ridges are not decorative. They exist because muscles and connective tissue pull on them. The ligamentum nuchae, a strong fibrous band running down the back of the neck, attaches firmly to the EOP at the top of the crest. That ligament is formed by the interweaving fibers of the upper trapezius, splenius capitis, and rhomboid minor muscles, and it spans from the EOP down to the prominent vertebra at the base of the neck.1Clinical Anatomy. Clinical Anatomy of Ligamentum Nuchae The nuchal lines, meanwhile, give attachment to the trapezius and semispinalis capitis muscles, both of which play major roles in extending and stabilizing the head. Because bone remodels in response to mechanical stress throughout life, the size and roughness of all these ridges reflect how much tension the overlying muscles and ligaments exert over time.
How the Occipital Bone Develops
The occipital bone is unusual because it forms through two different processes. Parts of it start as cartilage that gradually turns to bone (endochondral ossification), while other parts form directly from membrane without a cartilage stage. This dual origin begins as early as the ninth week of fetal development.2PubMed. The human occipital bone: review and update on its embryology and molecular development The upper portion of the squamous (flat) part of the occipital bone, including the area between the superior and highest nuchal lines, ossifies in membrane from paired centers.3PubMed Central. Ossification of the membranous portion of the squamous part of the occipital bone in man
At birth, the occipital crest region is smooth and barely perceptible. The ridges that will eventually become pronounced develop gradually through childhood and adolescence as the muscles of the neck and jaw grow stronger and exert increasing traction on the bone surface. This process mirrors what happens at other sites in the skeleton where tendons and ligaments attach: the bone slowly remodels, building up ridges and bumps in proportion to the forces applied.
Sex Differences in the Occipital Crest Region
If you compared the back of a male skull to a female skull, the differences around the occipital crest would be among the most obvious. Males tend to have a more prominent EOP, thicker and rougher nuchal lines, and a more developed external occipital crest. A CT-scan study from Northwest India found that these features were reliable enough for forensic use, achieving about 89% accuracy in estimating sex from the EOP region alone. The study classified EOP morphology into three types and found the most prominent form in about 38% of males but far less often in females, where a flatter form was the most common shape.4Forensic Imaging. Sex Estimation Through External Occipital Protuberance Morphology: A CT Scan Study in Northwest India
Research using three-dimensional surface scans of the occipital bone has confirmed that males consistently show deeper protuberances, longer distances from certain skull landmarks to the inion (the most projecting point of the EOP), and rougher surface texture including more pronounced nuchal lines and nuchal crest presence.5bioRxiv. Sexual dimorphism and biomechanical loading in occipital bone morphological variation In radiographic studies, the sex difference shows up starkly in measurements: one study of young adults found that enlarged EOPs were present in about 67% of males compared with about 20% of females, with the average size in males roughly 50% larger.6PubMed Central. A morphological adaptation? The prevalence of enlarged external occipital protuberance in young adults
The driving force behind this dimorphism is primarily hormonal and mechanical. Testosterone promotes greater muscle mass in the neck and jaw, which translates to more force applied at attachment sites on the skull. Over decades, these forces sculpt the bone surface, making ridges and bumps more pronounced. That said, the shape of the occipital bone is not purely sex-linked. Ancestry also plays a role: three-dimensional morphometric studies have found meaningful differences in the proportions of the occipital bone among populations of Asian, African, and European descent, including variation in the width between asterion landmarks, the angle of the clivus, and the relative position of the inion.7PubMed Central. Three-dimensional geometric morphometric studies of modern human occipital variation
The “Phone Bone” Controversy
In 2018, Australian researchers published a study reporting that enlarged bony projections at the EOP were surprisingly common in young adults aged 18 to 30, occurring more frequently in that age group than in any older group.8PubMed Central. Prominent exostosis projecting from the occipital squama more substantial and prevalent in young adult than older age groups The researchers proposed that the cause was the widespread use of smartphones and tablets. When you look down at a screen for hours, your head tilts forward, increasing the mechanical load on the muscles and ligaments attached to the back of the skull. Over time, this sustained forward head posture could theoretically stimulate bone growth at the EOP, producing what the researchers termed an enlarged external occipital protuberance, or EEOP.
The media loved it. “Horns growing on young people’s skulls because of phone use” made headlines around the world. And the underlying biomechanics were not implausible. Mechanical load on the cervical muscles is several times greater when seated with the neck flexed forward than in a neutral position, and the ligamentum nuchae and upper trapezius fibers insert directly onto the EOP. As forward head posture increases, the tension at that attachment point increases.9PubMed Central. The Association of Occipital Spur with Craniocervical Posture and Craniofacial Morphology A case series of teenagers with large bony growths at the EOP found that all of them had markedly forward head posture, with no genetic markers or inflammatory signs to explain the bone growth, suggesting mechanical load was the culprit.10PubMed. Large enthesophytes in teenage skulls: Mechanical, inflammatory and genetic considerations
But the smartphone angle was always the weakest part of the argument. The original researchers themselves acknowledged that plenty of activities involving sustained forward head flexion, like cycling with drop handlebars or sleeping on a high pillow, have been common for decades and could not explain why the phenomenon appeared to be concentrated in younger adults.11PubMed Central. Prominent exostosis projecting from the occipital squama more substantial and prevalent in young adult than older age groups
What the Data Actually Show
A retrospective study from Yale compared lateral skull X-rays taken in 2007 (the year the iPhone launched) with X-rays from 2017, looking specifically for exophytic (outward-growing) bony projections at the EOP. If smartphones were causing the growths, you would expect higher rates in the 2017 group. The results went the other direction: 50% of the 2007 group had an exophytic EOP, compared with about 33% of the 2017 group. When the researchers ran a logistic regression accounting for age, sex, and access to the iPhone era, only male sex had a statistically significant association with having a bony projection, with an odds ratio of about 6. Neither age nor whether the patient’s X-ray came from the pre- or post-iPhone era mattered.12PubMed Central. Exophytic External Occipital Protuberance Prevalence Pre- and Post-iPhone Introduction: A Retrospective Cohort
When the projections were present, they were also larger in males, averaging about 11 mm compared with about 3 mm in females. Size was not related to age or to whether the X-ray came from before or after smartphones became ubiquitous.13PubMed Central. Exophytic External Occipital Protuberance Prevalence Pre- and Post-iPhone Introduction: A Retrospective Cohort The picture that emerges is that being male is by far the strongest predictor of having a large bump at the back of your skull, which aligns neatly with the long-established sex dimorphism in the region rather than with any recent change in screen habits.
That does not mean forward head posture is irrelevant. Mechanical load clearly contributes to bone growth at entheses (places where tendons and ligaments attach to bone) throughout the body, and the EOP is no exception. But the leap from “posture affects bone” to “smartphones are giving young people skull horns” skipped over the much simpler explanation that the bumps have always been common, that males have always had bigger ones, and that the age pattern may reflect the fact that bone remodeling at tendon attachment sites is most active during the years of peak physical activity and muscle development.
Radiographic Classification
Clinicians and researchers who study the EOP region typically classify what they see on lateral X-rays into a few morphological types. A recent classification system used in studies of cervical myelopathy patients divides EOP shapes into three categories: a flat type (Type I), a crest type (Type II), and a spine type (Type III), with the spine type representing the most prominent bony projection.14PubMed Central. Gender-specific patterns of external occipital protuberance hyperplasia: associations with nuchal ligament ossification and cervical sagittal imbalance in myelopathy patients The threshold commonly used in research for an “enlarged” EOP is a projection exceeding 10 mm on a lateral radiograph.15PubMed Central. The influence of age, biological sex, anthropometrics, and neck characteristics on external occipital protuberance size
Knowing your classification type is not terribly useful as a patient unless the projection is causing symptoms, which brings us to the clinical side.
When the Bump Causes Pain
Most people with a prominent occipital crest or EOP never know it is there unless someone points it out on an X-ray. But in a small number of cases, a large bony spur at this site can press on or irritate the greater occipital nerve, which runs just lateral to the midline at the back of the skull. The result can be persistent pain at the base of the skull, tenderness to touch, and in some cases occipital neuralgia, a condition involving shooting or electric-shock-like pain radiating from the back of the head toward the top of the scalp.16PubMed Central. Occipital spur: understanding a normal yet symptomatic variant from orthodontic diagnostic lateral cephalogram
A case report described an adolescent with intractable posterior migraines traced to a large occipital spur compressing the neighboring nerves. After a nerve block confirmed the diagnosis, surgeons excised the spur and decompressed the greater occipital nerves. The patient experienced immediate and sustained relief, stopped taking migraine medications, and returned to normal school attendance for at least six months of follow-up.17FACE. The Surgical Management of an Occipital Spur Contributing to Intractable Posterior Migraines in an Adolescent
Surgical excision is rare and reserved for cases where conservative approaches have failed. For most people with mild tenderness at the back of the skull, the bump is incidental and the discomfort, if it exists at all, is manageable with postural correction, stretching, or occasional analgesics. If you can feel a pronounced bump at the back of your head and it is tender or associated with headaches radiating upward, it is worth mentioning to a clinician, not because it is dangerous but because targeted treatments exist if the nerve involvement is confirmed.
Occipital Ridges in Other Primates
The occipital crest and its associated nuchal lines are not unique to humans. In fact, they are far more dramatic in many of our primate relatives. As the permanent teeth erupt in primates and the facial skeleton outgrows the braincase, the expanding temporalis and nuchal muscles drive the formation of bony crests in the occipital region and sometimes along the midline of the skull roof as well.18Proceedings of the Zoological Society of London. Cranial Crests in the Anthropoidea
Gorillas have some of the most pronounced cranial cresting of any living primate. Among western lowland gorillas, roughly 93% of males and 58% of females develop a sagittal crest running along the top of the skull, with corresponding heavy nuchal ridges at the back. Bornean orangutans show cresting in about 39% of males but no females. Eastern chimpanzees fall in between, with about 24% of males and 7% of females carrying a sagittal crest.19PubMed Central. Sagittal crest formation in great apes and gibbons The traditional explanation, that crests simply grow to accommodate ever-larger jaw muscles, has recently been challenged. A study of gorillas and orangutans found that while some statistical association exists between the sagittal crest and jaw-muscle regions, patterns of variation in the crest, mandibular ramus, and coronoid process cannot be fully explained by muscle attachment alone.20PubMed Central. Evaluating the muscle attachment hypothesis for sagittal cresting in Gorilla and Pongo
In the fossil record, the occipital region has been a key area for distinguishing between hominin species. Asian Homo erectus specimens are known for a thick occipital torus, a bar of bone running horizontally across the back of the skull. However, comparative analysis has shown that this feature, while striking, does not actually set Asian H. erectus apart from other robust-skulled hominins when you account for overall skull size and proportions. Chimpanzees and bonobos, by contrast, show a very high position of the inion and an anteroposterior compression of the occipital bone, features partly related to their smaller cranial size relative to hominins.21Journal of Human Evolution. Where are inion and endinion? Variations of the exo- and endocranial morphology of the occipital bone during hominin evolution
Robusticity Is Not Always Ancestral
A common assumption in physical anthropology is that a more rugged, heavily ridged skull is a primitive trait, a holdover from earlier, more robust ancestors. The occipital crest region has featured prominently in that debate. Some modern human populations, such as Australian Aboriginal peoples, show pronounced cranial robusticity including well-developed nuchal lines and occipital crests. But research has argued that this does not represent a survival of some ancient condition. Instead, the pattern in Australia appears to reflect the specific history of that population, including size reduction (smaller overall skulls) with the maintenance of robusticity, likely shaped by particular selective pressures during the long occupation of the continent.22Journal of Human Evolution. The question of robusticity and the relationship between cranial size and shape in Homo sapiens
This finding matters beyond the academic sphere because it dismantles a simplistic narrative in which some living humans have “more evolved” or “less evolved” skulls. Cranial features like the occipital crest respond to a tangle of genetic, hormonal, mechanical, and demographic forces. Two skulls can look superficially similar in the occipital region for entirely different reasons, and reading evolutionary status from a single anatomical feature has proven unreliable.
Nuchal Ligament Ossification and Cervical Spine Problems
An area of active clinical research is the relationship between prominent EOP morphology and ossification of the nuchal ligament, a process in which the ligamentum nuchae gradually converts to bone along its length. This ossification can appear on X-rays as a chain of bony deposits descending from the EOP along the cervical spine. Researchers studying patients with cervical myelopathy (spinal cord compression in the neck) have begun classifying EOP shape alongside the extent of nuchal ligament ossification and cervical sagittal alignment, looking for patterns that might predict which patients develop more severe symptoms.23PubMed Central. Gender-specific patterns of external occipital protuberance hyperplasia: associations with nuchal ligament ossification and cervical sagittal imbalance in myelopathy patients
The logic is straightforward: if the forces that enlarge the EOP also promote ossification of the ligament below it, and if that ossification alters how the cervical spine moves and balances, then EOP morphology could serve as a simple screening marker visible on a standard lateral neck X-ray. This work is still in early stages, and it would be premature to say that a large bump on the back of your skull predicts neck problems. But it highlights that the occipital crest region is not a static anatomical curiosity. It is a living interface between bone, ligament, and muscle that continues remodeling throughout life in response to posture, activity, hormones, and aging.