Smile lines around the nose and mouth are formally called nasolabial folds. Smile lines at the outer corners of the eyes are called crow’s feet, or lateral canthal lines in clinical settings. Both types form from repeated muscle contractions during smiling, and both can deepen permanently with age.
Nasolabial Folds: The Lines by Your Mouth
Nasolabial folds are the pair of creases that run from the sides of your nose down to the corners of your mouth. Nearly everyone has them to some degree, even in childhood, because they mark the natural boundary between the cheek and the upper lip. The more precise anatomical term is actually “melolabial fold,” meaning the crease between the cheek (melo-) and the lip, though nasolabial fold is the name used in virtually all clinical and cosmetic contexts.
These folds appear when you smile because several muscles pull your lip corners upward and outward. The main driver is a muscle called the zygomaticus major, which connects your cheekbone to the corner of your mouth. When it contracts, it tugs your mouth into a grin, and the skin between your cheek and lip bunches into that familiar crease. Other muscles that lift the upper lip contribute to the fold’s shape, and the specific balance between these muscles is part of why everyone’s smile looks slightly different.
Crow’s Feet: The Lines by Your Eyes
The other set of smile lines fans out from the outer corners of your eyes. These are commonly called crow’s feet and clinically referred to as periocular lateral wrinkles or lateral canthal lines. They form because the ring-shaped muscle surrounding each eye (the orbicularis oculi) contracts when you smile genuinely, squeezing the skin at the temples into small radiating creases.
A genuine smile, sometimes called a Duchenne smile, involves both the mouth-pulling muscle and this eye muscle working together. That’s why crow’s feet tend to appear during real smiles but not forced ones. The exact pattern of these wrinkles varies from person to person. The most common pattern (about 35% of people) is a set of radiating lines fanning outward from the eye corner toward the eyebrow. Around 20% of people show a “miniature crow’s feet” pattern with shorter, more curved lines clustered near the corner of the eye.
Dynamic vs. Static: When Lines Become Permanent
Smile lines start out as dynamic wrinkles, meaning they only show up when your facial muscles are actively moving. You smile, the lines appear; you relax your face, they vanish. Over time, though, repeated folding of the skin in the same spot breaks down the structural fibers that keep skin bouncy, and those creases begin to stick around even at rest. At that point, they’ve become static wrinkles.
A simple way to check which type you have: relax your face completely in front of a mirror. Lines that disappear are still dynamic. Lines that remain visible are static. Most people transition from dynamic to static smile lines gradually through their 30s and 40s, though the timeline varies widely depending on genetics, sun exposure, and skin type.
Why Smile Lines Deepen With Age
Deepening nasolabial folds aren’t just about the skin wrinkling. Several layers of your face change simultaneously, and together they make the fold more pronounced.
The cheek fat pad, a cushion of fat that gives your midface its youthful fullness, sits directly above the nasolabial fold. In youth, it’s round and plump, held in place by a honeycomb-like network of connective tissue fibers that anchor the fat to the muscles and skin beneath it. With aging, two things happen. First, the fat itself deflates, shrinking in volume. Second, the connective fibers that hold everything in place lose their elasticity and stretch out. The result is a cheek fat pad that sags downward and flattens, no longer filling out the midface the way it used to.
On top of that, the bone underneath your upper jaw gradually resorbs, pulling the foundation of the soft tissue backward. Combined with muscle thinning around the mouth, this can cause up to a 40% decrease in the soft tissue thickness of the area. It’s the combination of bone loss, fat deflation, and connective tissue stretching that makes nasolabial folds deepen, not just skin aging on its own. This is why skincare alone has a limited effect on deep folds: the structural scaffolding beneath the skin has changed.
What Actually Helps Reduce Them
For dynamic smile lines that are just beginning to show at rest, topical retinol (vitamin A) can help. Retinol stimulates skin renewal and collagen production, and clinical data shows it can meaningfully improve the appearance of both crow’s feet and nasolabial folds over time, particularly when formulated with ingredients that boost its activity in the skin. Results are gradual, typically appearing over weeks to months of consistent use, and most effective on finer, shallower lines.
For deeper, established nasolabial folds, injectable fillers made of hyaluronic acid (a sugar-based gel naturally found in skin) are the most common treatment. The filler is placed beneath the fold to restore lost volume, essentially re-inflating the area that has deflated. Results are immediate, but the filler gradually breaks down. Ultrasound studies tracking filler in the nasolabial fold found that dermal thickness increased by about 40% right after injection but dropped to roughly 12% above baseline by 48 weeks. In practical terms, most people see their results last somewhere between 6 and 12 months before a touch-up is needed, depending on the specific product used and their body’s rate of breaking it down.
For more advanced aging where the cheek fat pad has significantly descended and the fold is deep and structural, fillers alone may not fully address the problem. Surgical midface lifting repositions the sagging fat pad and tightens the stretched connective tissue, addressing the root cause rather than masking it with added volume. This is typically considered when fillers no longer produce a satisfying result or when the surrounding cheek has noticeably lost its shape.
Why Some People Get Deeper Lines Than Others
Genetics play a large role. Skin thickness, fat distribution, bone structure, and even the exact direction your facial muscle fibers run all vary from person to person and influence how prominently smile lines form. People with thinner skin or less subcutaneous fat in the midface tend to develop visible nasolabial folds earlier. Those with stronger or more active smiling muscles may develop crow’s feet sooner. Sun damage accelerates the breakdown of collagen and elastin throughout the face, making all types of smile lines appear earlier and deepen faster than they otherwise would.