A downturned smile happens when the corners of your mouth naturally pull downward instead of staying neutral or lifting up. This can be caused by a specific facial muscle doing too much work, age-related changes in skin and fat, habits like teeth grinding, or in some cases a nerve issue that needs medical attention. Most of the time it’s a cosmetic concern with straightforward explanations, but understanding the cause helps you figure out what (if anything) to do about it.
The Muscle That Pulls Your Mouth Down
The main driver of a downturned smile is a small muscle called the depressor anguli oris, or DAO. It runs from your jawbone up to the corner of your mouth, and its job is to pull your mouth corners downward. You use it when expressing disgust or frowning. In some people, this muscle is naturally stronger or more active than the muscles that lift the mouth corners, creating a resting expression that looks sad or displeased even when you feel perfectly fine.
This imbalance can also develop after a period of facial nerve weakness. When the nerve recovers, the DAO sometimes starts firing at the same time as the muscles that lift your smile. You can actually feel this happening by placing a finger along the crease that runs from the corner of your mouth toward your chin (the marionette line) and smiling. If you feel a taut cord pulling under the skin, that’s the DAO contracting and fighting against your smile.
Aging and Skin Changes
As you get older, your skin produces less collagen and elastin, the proteins responsible for firmness and bounce. Fat pads in the midface gradually shift downward, and the bone structure of the jaw subtly shrinks. Together, these changes cause the tissue around the mouth to sag, making the corners appear to droop. The creases that form from the mouth corners down toward the chin (marionette lines) deepen over time and visually emphasize the downward pull.
This process doesn’t happen at the same pace for everyone. Sun exposure and smoking both accelerate it significantly. A study of 966 people found a strong association between cumulative sun exposure and the breakdown of elastic tissue in facial skin, across both men and women. Smoking showed a similar damaging effect. If you’ve spent years in the sun without protection or have a smoking history, these lower-face changes tend to show up earlier and look more pronounced.
Teeth Grinding and Jaw Clenching
Bruxism, the habit of grinding or clenching your teeth, is an often-overlooked cause of a downturned mouth. Chronic clenching enlarges the jaw muscles, giving the lower face a wider, squarer look. But the less obvious effect is what it does over time: bruxism accelerates bone loss in the jaw and wears down teeth, reducing the structural support your lower face depends on. As that support shrinks, the mouth corners turn down, jowls develop, lips thin out, and the overall face ages faster than it otherwise would.
Many people with bruxism don’t realize they have it because it often happens during sleep. Signs include waking up with jaw soreness or headaches, noticing flattened or chipped teeth, or hearing from a partner that you grind at night. If your smile has changed and you recognize any of these symptoms, bruxism could be contributing.
When a Downturned Smile Is a Medical Concern
A smile that suddenly drops on one side is a different situation entirely from a gradual cosmetic change. The two most important causes of sudden facial drooping are Bell’s palsy and stroke, and telling them apart matters.
Bell’s palsy is a temporary weakness of the facial nerve. It typically affects people between ages 30 and 50, develops gradually over hours or days, and affects the entire half of the face, including the forehead. You’ll likely have trouble closing the eye on the affected side. Pain near the ear, heightened sensitivity to sound, and changes in taste are common. Low vitamin C levels have been identified as a possible triggering factor, though the exact cause in most cases involves viral inflammation of the nerve.
A stroke, by contrast, strikes suddenly, over seconds. It usually affects people over 60 and causes drooping in the lower face only, typically sparing the forehead. You can usually still close your eye. The critical difference is that a stroke comes with other symptoms: weakness in an arm or leg, slurred speech, or vision changes. If drooping appears suddenly alongside any of those, it’s a medical emergency.
Cosmetic Treatments That Help
For an overactive DAO muscle, small amounts of botulinum toxin (Botox) can relax the downward pull and let the corners of the mouth sit in a more neutral or slightly lifted position. The typical dose is quite small, around 4 to 8 units per side, because the muscles around the mouth are delicate and over-treating them can temporarily affect expressions like puckering or drinking through a straw.
For volume loss and marionette lines, injectable fillers made of hyaluronic acid (a substance your skin produces naturally) can restore support to the lower face. Results typically last 6 to 12 months depending on the product used, with some thicker formulations lasting up to two years. Fillers work by physically replacing lost volume, so they address the structural cause rather than just relaxing a muscle.
Some providers combine both approaches: Botox to quiet the DAO and filler to rebuild the scaffolding that gravity and time have worn away. The combination tends to produce a more balanced result than either treatment alone.
What You Can Do at Home
Protecting your skin from further collagen breakdown is the most impactful thing you can do without a clinic visit. Daily sunscreen on your face, even on cloudy days, slows the elastic tissue damage that leads to sagging. If you smoke, stopping removes one of the strongest accelerators of lower-face aging.
If you suspect bruxism, a night guard from your dentist can reduce the jaw clenching that wears down bone and teeth over time. Addressing the grinding won’t reverse changes that have already happened, but it prevents continued acceleration of the aging process in your lower face.
Facial exercises aimed at strengthening the muscles that lift the mouth corners are widely recommended online, but clinical evidence supporting their effectiveness for this specific concern is limited. They’re unlikely to cause harm, but expectations should be modest compared to treatments that directly address muscle imbalance or volume loss.