The upper lip dimple is a distinct facial feature characterized by a small, often vertical, indentation that becomes visible just above the vermillion border of the mouth when a person smiles. This depression occurs in the philtrum, the vertical groove located in the center of the upper lip, extending from the base of the nose to the Cupid’s bow. It is a subtle but noticeable variation in facial anatomy. While often confused with cheek dimples, the upper lip dimple is centrally located and tends to have a more elongated shape, unlike the rounded, lateral cheek dimples.
The Muscular Mechanism Causing the Dimple
The formation of the upper lip dimple is directly tied to the unique structure and action of a specific facial muscle known as the Levator labii superioris alaeque nasi (LLSAN). This muscle, which has the longest name of any in the human body, is responsible for elevating the upper lip and dilating the nostril, contributing to expressions like a sneer or a strong smile. It originates near the side of the nose and extends downward, inserting into the skin of the upper lip and the lateral part of the nostril.
The dimple itself does not arise from a muscle split, as is theorized with cheek dimples, but rather from a tight, short, or anomalous attachment of the LLSAN muscle fibers to the overlying skin. In individuals with this feature, the muscle’s connective tissue fibers are tethered unusually close to the dermis in the philtrum area. When a person smiles, the LLSAN muscle contracts and pulls upward, causing the skin to be drawn inward at the point of this fixed attachment. This inward pull creates the characteristic vertical depression just above the lip line.
This anatomical variation represents a natural deviation in the muscle-to-skin connection. The LLSAN muscle is the primary mechanism for any dynamic indentation occurring in the upper mid-face region near the nose. Because this muscle is vertically oriented and works to lift the lip, its tethering effect results in the vertical orientation of the upper lip dimple. The dynamic nature of the upper lip dimple means it is only apparent during muscle contraction, such as when laughing or smiling.
Genetics and Frequency of the Upper Lip Dimple
Facial dimples, including the upper lip variant, are understood to have an inherited component, though the exact genetic mechanism is complex. The genetics for the upper lip dimple are less studied than cheek dimples. These facial characteristics are generally polygenic, meaning they are influenced by multiple genes rather than a single gene.
The anatomical variation causing the upper lip dimple is passed down through genetic predisposition, similar to other facial muscle variations. Specific population-level studies focusing on its prevalence are scarce, leading to a lack of precise statistical data. This indentation is visibly less frequent than cheek dimples, which occur in roughly 20 to 30 percent of people globally. The infrequency suggests that the specific muscle-to-dermis tethering required is a rarer genetic outcome.
As with all facial dimples, the feature may also be transient, appearing prominently in childhood and then diminishing or disappearing entirely as the individual ages. Changes in facial fat distribution and the general stretching of facial muscles over time can cause the tethering effect to become less pronounced. The presence of the feature is a reflection of a familial trait, but its expression can vary significantly in depth and permanence between individuals.
Aesthetic Procedures for Modification
Individuals seeking to modify the appearance of an upper lip dimple have options ranging from surgical creation to non-surgical reduction. For those who desire the feature, a form of dimpleplasty can be performed to create or enhance the vertical indentation. This procedure involves a surgeon placing an internal suture through a small incision made inside the mouth, creating a permanent attachment between the underlying LLSAN muscle and the overlying skin. The resulting scar tissue acts as the tether that pulls the skin inward upon smiling, mimicking the natural formation of the dimple.
Conversely, a prominent or unwanted upper lip dimple can often be reduced or eliminated if the cause is dynamic, meaning it is due to muscle overactivity. A highly targeted treatment involves the use of neurotoxin injections, such as Botulinum toxin, placed directly into the LLSAN muscle. The neurotoxin works by temporarily relaxing the targeted muscle fibers, reducing the strength of the upward pull that creates the indentation when smiling. This relaxation lessens the tethering effect, causing the dimple to soften or disappear entirely for several months until the muscle function gradually recovers.
Surgical reduction is also an option for dimples caused by a permanent, static tissue tether. This involves a surgeon carefully releasing the specific fibrous band connecting the muscle to the dermis through an internal incision, allowing the skin to smooth out when the person smiles. All such procedures carry inherent risks, including temporary swelling, bruising, and the potential for asymmetry or an unnatural appearance if the tether release is not perfectly balanced.