The common term “crown” or “cowlick” refers to a phenomenon that occurs on nearly every human scalp. This feature is more formally known as the vertex hair whorl, a visually distinct pattern where hair grows in a circular motion. This simple spiral is the result of complex biological processes, revealing an intersection of genetics, developmental biology, and physical asymmetry.
Defining the Vertex Hair Whorl
The vertex hair whorl is a patch of hair that grows in a spiral pattern around a central point on the scalp. This anatomical feature is also known as a trichoglyph or parietal whorl, due to its location near the highest point of the head (the vertex). The whorl is created by the precise orientation of hair follicles, which emerge at a specific angle and align to follow a circular path.
Observing a hair whorl clearly requires short hair, as longer strands can mask the underlying pattern. It is a morphological feature, meaning it is a characteristic of the body’s form without a known functional purpose. The central point of the whorl is often visible and can sometimes create an area of thinly covered scalp. This apex of the spiral is where the hair strands separate to begin their circular trajectory, and it is not a “bald spot.”
The Question of Universality and Variations
The presence of a hair whorl is nearly universal in humans. Studies consistently show that over 95% of people have at least one of these spiral patterns. This high prevalence suggests the hair whorl is a standard part of human scalp development, considered a normal characteristic.
The most common variation involves the number of whorls present on the scalp. While a single vertex whorl is standard, a small percentage of the population exhibits a double whorl. These double spirals, sometimes called a double crown, are found in approximately 1.5% to 5% of individuals. Cases of a triple whorl are extremely rare.
These multiple whorls may spin in the same or opposite directions, and they can be situated close together or at different points on the scalp. The presence of two or more whorls does not carry any established significance regarding intelligence or health. Although the pattern may be more challenging to style, it represents a minor, normal deviation in hair follicle alignment.
Genetic Influence on Whorl Direction
The direction in which the hair whorl spirals (clockwise/dextral or counter-clockwise/sinistral) is influenced by genetic factors. A large majority of people have a clockwise-spinning whorl, estimated at 81% to over 90% of the population. The direction of the spiral has been studied due to its correlation with human handedness, another trait exhibiting population-level asymmetry.
Research suggests that genes determining hair whorl direction may be linked to those influencing handedness (right-handed or non-right-handed, including left-handed and ambidextrous individuals). Since most people are right-handed, the vast majority also display clockwise whorl rotation. Counter-clockwise whorls are seen infrequently in right-handed people, appearing in only about 8.4% of this group.
The association is less straightforward for non-right-handed people. Individuals who are left-handed or ambidextrous are statistically more likely to have a counter-clockwise whorl, with some studies finding this pattern in nearly 45% of left-handers. This supports the idea of a common genetic mechanism controlling both traits, where the expression in non-right-handers results in a more random or balanced mixture of the two directional patterns. The specific mechanism is complex, but the directional bias is a clear biological correlation.
Understanding Hair Whorl Formation
The specific pattern of the vertex hair whorl is set very early in human development, long before birth. Hair follicles begin to form on the scalp around the 10th to 14th week of gestation. This formation is a highly organized process where follicles are induced in a precise, evenly spaced pattern. No new hair follicles are formed after birth; the pattern established in utero remains for life.
The spiral itself is a result of biomechanical forces acting on the developing scalp. Between approximately 10 and 18 weeks of gestation, the fetal brain undergoes significant growth. This rapid expansion causes the delicate scalp skin to stretch and be placed under tension. The direction of this stretching and tension influences the final alignment and angle of the hair follicles, establishing the permanent circular pattern.