The nose is a complex, dynamic structure that changes shape during facial animation, contrary to being a fixed feature. This movement is particularly noticeable when smiling or laughing, resulting in a temporary widening of the nostrils and a downward movement of the nasal tip. This normal physiological occurrence is driven by the coordinated contraction of small facial muscles. Understanding this change requires examining the muscular connections linking the nose to the upper lip and maxilla.
The Muscular Mechanism Behind Nasal Movement
The primary anatomical structure responsible for the dynamic movement of the nasal tip and the widening of the base during smiling is the Depressor Septi Nasi (DSN) muscle. This small, paired muscle acts as a tether, pulling the flexible parts of the nose toward the upper jaw. It is considered an accessory muscle of facial expression, working in conjunction with the larger muscles that create the smile.
The DSN originates from the maxilla, specifically from the incisive fossa situated just above the medial incisor teeth. Its fibers insert directly into the mobile part of the nasal septum and the back portion of the alar cartilage, which forms the lower part of the nostril. When activated, the DSN pulls the nasal tip downward, contracting toward its point of origin.
When primary smile muscles, such as the orbicularis oris, contract to elevate the upper lip, the DSN contracts simultaneously. This linked action pulls the nasal tip down and shortens the distance between the nose and the upper lip. The lateral fascicles of the DSN also contribute to the outward movement of the alar cartilage, which is perceived as the widening or flaring of the nostrils.
Another muscle playing a secondary role is the Levator Labii Superioris Alaeque Nasi (LLSAN), often called the “snarl muscle.” This muscle runs alongside the nose and elevates the upper lip and the wing of the nose. The combination of the DSN pulling the tip down and the LLSAN pulling the alar base upward contributes to the overall dynamic distortion of the nose during a strong smile.
Structural and Genetic Factors Affecting Nasal Dynamics
The extent to which the nose widens or the tip descends during animation is not uniform across all individuals, largely due to inherent differences in nasal structure. The strength and resilience of the lower lateral cartilages, which give the nasal tip its shape and support, significantly influence this movement. Individuals with weaker or softer tip cartilages may experience a more pronounced downward pull and flaring when the DSN contracts.
The thickness of the nasal skin and the amount of soft tissue covering the cartilaginous framework also modulate the visible effect of muscle contraction. Thicker skin and soft tissue can dampen the effect of the underlying muscular forces, leading to less apparent dynamic movement. Conversely, those with thinner skin may show greater movement from the same degree of muscle pull.
The width of the nasal base, or alar width, is another structural factor that varies genetically and ethnically. In some ethnic groups, the natural prominence or hypertrophy of the lateral fascicles of the Depressor Septi Nasi is more common, which can predispose the individual to a wider alar flare when smiling.
Underlying genetic factors control the development and final morphology of the nasal structures, including the size and position of the nasal cartilages. The unique combination of cartilage size, ligament laxity, and soft tissue thickness determines the individual’s baseline nasal dynamics. This explains why some people have a prominent dynamic nasal change while others experience only a subtle shift in appearance.
Options for Managing Nasal Movement
For individuals seeking to limit the dynamic widening or tip depression that occurs while smiling, both temporary non-surgical and permanent surgical options exist. Non-surgical management focuses on reducing the contractile strength of the specific muscle responsible for the movement.
Targeted neuromodulators, such as botulinum toxin type A, are injected directly into the Depressor Septi Nasi muscle. This substance temporarily weakens the muscle’s pull on the nasal tip and alar base by blocking the nerve signals that cause contraction. The treatment is effective for reducing the downward and outward movement during smiling. However, the effects are temporary, typically lasting between three and four months, requiring repeat injections for maintenance.
Surgical intervention, typically performed as part of a rhinoplasty, offers a lasting solution by addressing either the muscle itself or the underlying nasal structure. A surgeon can permanently weaken, resect, or transpose the DSN muscle to eliminate its depressive action on the nasal tip. This procedure is often performed alongside other surgical techniques to strengthen the nasal tip support.
Tip Rhinoplasty
Tip Rhinoplasty involves reinforcing the structure of the nasal tip, often by using cartilage grafts. This creates a more rigid framework that resists the muscle’s pull.
Alar Base Reduction
For issues related to excessive nostril widening, a procedure known as alar base reduction, or Weir Excision, can be performed. This involves removing a small wedge of tissue from the nostril base to permanently narrow the alar width, providing a lasting correction to dynamic flaring.