Smile Lines: Why the Fold Is Structure, Not a Wrinkle

Smile lines, or nasolabial folds, run from the sides of your nose to the corners of your mouth. They are not really wrinkles. They mark a border where the fat of your cheek sits above a line held in place by muscle and fibrous tissue. Bone, fat and ligaments decide how deep that border looks. Below: the anatomy, what changes with age, what topical products can and cannot do, and what clinic treatments actually change.

What are smile lines?

The FDA defines nasolabial folds as the lines extending from the sides of the nose to the edges of the mouth. That is what most people mean by smile lines. Two other lines get confused with them. Crow's feet at the outer eye are sometimes called laugh lines, and marionette lines run down from the corners of the mouth.

The fold is anatomy first. In a cadaver study from San Francisco, researchers found the fold clearly on 14 of 16 bodies. They concluded that it is defined by structures that support the cheek fat and hold it above the fold. The everyday name comes from the way the fold deepens when you smile.

Why smile lines are structure, not a wrinkle

A wrinkle is a crease written into the skin. The collagen story behind that is covered in what causes wrinkles. A fold is different. It is a step between two structures that sit at different heights.

Look at what holds the step in place. The same cadaver study found two muscle bundles beneath the fold, one running parallel to it and one at right angles. Fibrous strands ran through the fat above it. Bodies with a poorly defined fold had fewer muscle bundles and fewer fibrous strands.

The fat is organized too. Dye studies in 30 cadaver half-faces showed that facial fat sits in separate compartments, and that the nasolabial fold is a discrete unit with distinct boundaries. The authors concluded that the face does not age as one mass. Aging, they wrote, is partly a matter of how each compartment changes.

Ligaments tie the system to the skeleton. A 2013 review describes the face's retaining ligaments as sitting in constant anatomic locations, where they separate facial spaces and compartments. Their extensions form the fibrous walls between fat compartments. None of these structures sits in the skin a cream is applied to.

What makes smile lines deeper with age?

Three layers change under the fold, and researchers still argue about how much each one matters.

• Bone. A CT study compared young and older adults. It found that the upper jaw bone beside the nose tends to sit further back with age, relative to the upper face. The authors proposed this as one factor in the fold. They had noticed that patients with a set-back upper jaw showed a prominent fold at an early age. A later CT study of 60 adults found the maxillary angle decreased with age in both men and women.
• Fat. A CT study of 12 cadaver heads found the midface fat compartments sat lower, and carried more of their volume low, in the older group. But a study that scanned 14 living adults about 10 years apart found superficial cheek fat stable in volume and position between roughly 50 and 60. The fat story is not settled.
• Skin. In 30 middle-aged women, more severe infiltration of fat into the dermis of the cheek went with lower skin elasticity and a more marked nasolabial fold. That was a correlation, not proof of cause. It suggests skin quality plays some part in how deep a fold looks.

The fuller four-layer picture, and which parts of it you can influence, is in what causes sagging skin.

Weight, sun and smoking

The best natural experiment here uses identical twins. Researchers photographed 186 pairs at a twins festival in Ohio. A 4-point higher body mass index went with an older look in twins under 40, but a younger look after 40. The same study linked more sun exposure and longer smoking with an older appearance.

That fits the structural picture. Volume under the midface softens the step at the fold, and losing it can sharpen the step. The study rated overall perceived age, not the fold itself, so treat that link as reasoning rather than a measured result. Which of these factors you control, and which you inherit, is sorted out in skin aging explained.

What topical products can and cannot do for smile lines

A cream acts on the skin. It can change how the surface over the fold looks. It cannot move fat, tighten a ligament or rebuild bone.

Here is what the surface can gain.

• Hydration. Moisturizer smooths the surface by flattening the valleys between skin ridges, and the effect usually lasts about 4 hours.
• A retinoid. A 26-week split-face trial tested 0.075 percent retinol in 57 Japanese women against a plain vehicle. Fine wrinkling improved in 50 percent against 24 percent, and deep wrinkling in 28 percent against 2 percent. That is skin texture, not the fold, and a 2021 review found major methodological flaws in this and the other positive retinol trials. Our retinol guide covers how to start.
• Daily sunscreen. A 4.5-year randomized trial in 903 adults found 24 percent less skin aging with daily use than with discretionary use.

Some cosmetic trials do report softer-looking folds. In one, 70 women completed 16 weeks of a two-step serum and cream or its base formula. Graders rated the treated group's nasolabial folds as visually improved compared with the base formula. A fold can look softer when the skin across it is smoother and better hydrated. The trial graded how the fold looked. It does not show that the fat, ligaments or bone beneath it changed.

Hyaluronic acid causes the most confusion. The molecule in a serum is not the gel a clinician places under a fold, and our piece on hyaluronic acid and molecular weight explains the difference.

Facial exercise has one small test. In a 20-week pilot, 16 of 27 middle-aged women completed a facial exercise program. Blinded raters scored their upper and lower cheek fullness as improved, but nasolabial folds at rest did not change. There was no control group, and the founder of the exercise program was a co-author.

What clinic treatments change

The treatments that change a fold work below the skin. The American Academy of Dermatology is blunt about the ceiling. It says a surgical lift such as a facelift gives the most dramatic results, and that anyone expecting facelift-like results from a jar will likely be disappointed. Nonsurgical tightening with ultrasound or radiofrequency tends to give gradual results, and the AAD says even minimally invasive tightening cannot match a surgical lift.

Fillers are the clinic option aimed at the fold itself. Nasolabial folds are among the uses the FDA lists for absorbable fillers, which the body breaks down over time, so the treatment may need repeating. A 2021 meta-analysis of randomized trials gives a sense of the curve. On a wrinkle severity scale, the average score fell from 3.2 to 1.8 one month after treatment, then drifted back to 2.5 by 12 months. Side effects were common and mostly minor: lumpiness, tenderness, swelling and bruising.

The serious risks are rare and real. The FDA's most concerning listed risk is filler blocking a blood vessel, which can cause tissue death, blindness or stroke. A review of 98 reported cases of vision changes after filler found 13.3 percent involved the nasolabial fold, and most cases of vision loss did not recover. The FDA also says no dermal filler is approved for over-the-counter use, and it has flagged serious adverse events with needle-free filler devices. If you are considering filler, the FDA advises choosing a licensed provider experienced in dermatology or plastic surgery, and never injecting yourself.

When a change in your smile lines is a medical sign

Slow deepening over years is aging. A sudden change on one side is not.

MedlinePlus lists drooping of the face, such as the eyelid or the corner of the mouth, among the signs of Bell palsy. It says to contact a provider right away if your face droops, and notes that a provider can check for more serious causes, such as a stroke. Sudden numbness or weakness of the face, especially on one side, is a warning sign of stroke, and MedlinePlus says to call 911 right away.

Frequently asked questions

At what age do smile lines appear?

The fold is part of normal facial anatomy. In one cadaver study, it was clearly visible on 14 of 16 bodies. It tends to deepen with age as the structures beneath it change. People whose upper jaw sits further back can show a prominent fold early, which one CT study used as a clue to the fold's origin.

Does smiling cause smile lines?

Smiling deepens the fold while you smile, because the cheek bunches up against a border that stays put. The depth of the fold at rest reflects the structures under it. We found no study showing that smiling less makes the fold shallower.

Can a cream get rid of smile lines?

No cream moves fat, ligaments or bone. A cream can make the skin across the fold smoother and better hydrated, and one 16-week trial reported visually improved folds against the base formula. The fold itself stays.

Does face yoga help smile lines?

The one pilot study we found showed improved cheek fullness in 16 women after 20 weeks, but no change in the nasolabial folds at rest. It had no control group and a high dropout rate. It is not evidence that exercise shallows the fold.

How long do fillers for smile lines last?

It depends on the material and the area. A meta-analysis of randomized trials found the biggest improvement at one month, with part of it lost by 12 months. The FDA notes that absorbable fillers break down over time, so results need repeat treatment to maintain.

Why do my smile lines look deeper after losing weight?

Volume under the cheek softens the step at the fold, and losing it can make the step sharper. In a study of identical twins, a higher body mass index went with a younger look after 40. That study rated overall age, not the fold, so the link is reasoning rather than a direct measurement.