The appearance of a face that perpetually seems sad or displeased, commonly referred to as a “permanent sad face,” is a recognized anatomical condition, though the name is not clinical. This distinctive look is characterized by mouth corners that angle downward even when facial muscles are completely at rest. This unintentional effect can convey emotions like anger or sadness to others, even when the individual feels neutral. The underlying cause is rooted in an imbalance of the muscles controlling the lower face, which modern medicine can understand and correct.
The Anatomy Behind the Downturned Mouth
The primary anatomical structure involved in creating a downturned mouth is the Depressor Anguli Oris (DAO) muscle. This paired muscle originates on the lower jawbone (mandible) and inserts into the skin and muscle at the corners of the mouth. The DAO muscle’s function is to pull the angle of the mouth downward, which is necessary for expressions of frowning or sadness.
The DAO is controlled by the marginal mandibular branch of the seventh cranial nerve (CN VII). When this muscle is genetically overdeveloped or becomes overactive with age, its constant downward pull dominates the opposing muscles that lift the mouth corners. This creates the visual effect of a perpetual frown, even when the face is relaxed.
Congenital Versus Acquired Causes
The origins of a downturned mouth fall into two categories: congenital (present from birth) and acquired (developing later in life).
Congenital Causes
A congenital cause is medically known as Congenital Hypoplasia or Agenesis of the Depressor Anguli Oris Muscle (CHDAOM). In this rare developmental condition, the DAO muscle on one side is either underdeveloped (hypoplasia) or entirely absent (agenesis). This typically affects 3 to 6 out of every 1,000 live births.
This hypoplasia results in “asymmetric crying facies,” where the fully developed DAO muscle pulls one side of the mouth down during crying, while the weak or absent muscle on the other side fails to pull its corner down. This muscular anomaly is sometimes associated with other developmental issues, such as Cayler Cardiofacial Syndrome, which involves coexisting cardiac defects. If the condition is isolated, it is considered a benign cosmetic concern.
Acquired Causes
Acquired causes, which develop over time, are far more common and are often linked to the aging process. As people age, the skin loses elasticity and underlying facial fat pads diminish, leading to a loss of structural volume around the mouth. This volume loss, combined with the constant pull of a strong DAO muscle, allows the mouth corners to droop and deepens the vertical creases known as marionette lines.
The acquired appearance can also result from neurological events, such as a stroke, facial trauma, or temporary conditions like Bell’s Palsy. In these instances, damage often affects the facial nerves controlling the muscles responsible for lifting the mouth corners, such as the zygomaticus major. When lifting muscles are weakened, the unopposed action of the DAO muscle can create a pronounced, asymmetrical downward pull.
Clinical Diagnosis and Differentiation
Diagnosis is confirmed primarily through a detailed physical examination by a clinician, often a neurologist or plastic surgeon. The process begins with observing the face at rest to note the degree of downward angling and any asymmetry at the mouth corners. The provider also observes the patient performing voluntary facial movements, such as smiling and frowning.
This observation is crucial for distinguishing between a primary DAO issue and facial nerve palsy. For example, in congenital hypoplasia, asymmetry is typically noticeable only when the infant is crying, while forehead and eye movements remain symmetrical. If a neurological disorder is suspected, electrophysiological studies, such as electromyography (EMG), may be used to assess the function of facial muscles and nerves.
Management and Corrective Treatment
Treatment for a downturned mouth aims to either weaken the muscle pulling the corners down or provide structural support to lift them up. Non-surgical options are highly effective for most acquired cases where the DAO muscle is overactive.
Non-Surgical Treatments
Botulinum Toxin (Botox) is injected directly into the DAO muscle to temporarily block the nerve signals that cause contraction. Relaxing the overactive DAO shifts the natural balance of facial muscles, allowing the mouth corners to relax or lift slightly, which can also soften marionette lines. Dermal fillers, often composed of hyaluronic acid, are used to restore lost volume around the mouth and chin. Fillers physically prop up drooping mouth corners and provide structural support to counteract the downward effects of gravity and muscle tension.
Surgical Treatments
For congenital cases or when non-surgical methods fail, surgical intervention may be considered. Surgical options include a corner lip lift, a minor procedure involving the excision of a small piece of skin above the mouth corner to physically elevate the angle. More complex reconstructive procedures might involve muscle transfer or release to create symmetry and improve the resting position of the mouth, especially in cases of significant congenital hypoplasia.