Nasolabial folds (smile lines): causes and treatment

Why do nasolabial folds form?

Nasolabial folds are the lines that run from the sides of the nose down toward the corners of the mouth, and they are a common cosmetic concern that has a large influence on facial appearance ^[1]. As the fat over the cheekbones descends with age, the nasolabial folds deepen and the groove under the eyes also becomes more prominent ^[4].

A 2025 review, focusing on Korean patients, divided nasolabial folds into three types caused by volume loss, sagging tissue, and muscle attachment, and explained that each type needs a tailored treatment approach ^[1]. It also noted that it is not uncommon for one person to have two types at once ^[1]. This means that even folds that look alike may call for different methods if their causes differ.

Types of treatment

One of the methods commonly used for nasolabial folds is injecting filler (tissue filler). A 2021 meta-analysis described filler injections as one of the most commonly performed cosmetic procedures ^[2]. The meta-analyses reviewed here studied hyaluronic acid and calcium hydroxylapatite fillers ^{[5, 6]}.

If sagging is the main cause, surgical methods may also be discussed. The midface is understood as the area that includes the cheek from the lower eyelid down to the nasolabial fold, and various surgical techniques have been used, such as skin excision, skin-muscle flaps, repositioning of fat pads, and subperiosteal lifting (lifting beneath the membrane covering the bone) ^[7]. The extended SMAS facelift also mainly targets the change in which cheek fat descends and deepens the nasolabial folds ^[4].

Combining treatments such as botulinum toxin, fat-dissolving injections, and thread lifts was presented as an area that needs further research ^[1].

How long do filler results last?

A 2021 meta-analysis pooled randomized clinical trials of filler for nasolabial folds and analyzed changes in the Wrinkle Severity Rating Scale (WSRS) ^[2]. A lower score on this scale means the wrinkles are less visible. The score, which averaged 3.23 before treatment, dropped to 1.79 after 1 month, then rose again over time to 2.02 after 6 months and 2.46 after 12 months ^[2].

The authors concluded that filler can produce satisfying and lasting improvement ^[2]. However, the numbers show that among the time points measured, the improvement was greatest after 1 month and gradually decreased through 12 months ^[2]. In a 2013 meta-analysis, the wrinkle score at 6 months had also improved by an average of 1.21 compared with before treatment ^[5]. How long results last can vary depending on the material and the condition of your skin.

Does the type of filler make a difference?

Hyaluronic acid fillers are sometimes divided into monophasic and biphasic fillers based on how they are cross-linked ^[3]. In a 2022 meta-analysis of 11 randomized clinical trials with 935 participants, monophasic fillers had better wrinkle scores and overall cosmetic improvement scores than biphasic fillers, with no significant difference in pain or adverse reactions ^[3]. However, in their conclusion, the authors summarized that the effectiveness and tolerability of monophasic fillers are comparable to those of biphasic fillers ^[3]. A 2013 meta-analysis also reported that monophasic fillers were more effective over 6 months while biphasic fillers were better tolerated (tolerance), and the effectiveness and rate of adverse reactions differed by product family ^[5].

A 2024 meta-analysis of hyaluronic acid fillers mixed with the local anesthetic lidocaine found no significant difference in wrinkle scores, while pain scores were significantly lower ^[8]. There was also no significant difference in the rate of experiencing one or more adverse reactions ^[8]. In a subgroup analysis, the effect appeared more pronounced in East Asian patients, but the authors stated that further research is needed because there were few relevant studies ^[8].

In a 2016 meta-analysis that pooled 4 randomized studies of calcium hydroxylapatite filler injected into the nasolabial folds, the studies that compared it with hyaluronic acid filler found no significant difference in the occurrence of hematomas (collections of blood) and nodules ^[6]. Because only a small number of studies were included, it is difficult to generalize these results widely.

Side effects and what to know for safety

In the 2021 meta-analysis, the common side effects were lumpiness (43%), tenderness (41%), swelling (34%), and bruising (29%) ^[2]. It is a good idea to know in advance that these reactions can occur, and to contact the clinic where you were treated right away if symptoms persist or get worse.

The nasolabial fold area moves a lot, so filler placed incorrectly can easily migrate ^[1]. The 2025 review stressed that for safe injection, it is important to understand anatomical differences, especially the course of the facial artery in Korean patients ^[1]. The same review also examined injecting with a needle versus a cannula (a thin, blunt-tipped tube) and injecting in separate shallow and deep layers, but it should be kept in mind that it was written based on experience with a specific filler product ^[1].

Most of the research summaries for the studies included in the meta-analyses do not state the ethnicity of the participants, so it is difficult to say for certain that the same figures would apply to Korean patients.

What to check during your consultation

The causes of nasolabial folds differ from person to person, and several causes can overlap in one person. The size of the effect and how long it lasts also depend on the material and the condition of your skin, so it is a good idea to check the following during your examination.

• Whether your nasolabial folds come from volume loss, sagging, or the muscles
• The type of material to be used and how long it is expected to last
• The anesthesia method and how pain is managed during treatment
• Common side effects and how to get in touch if unusual symptoms appear
• Whether your condition is better suited to a surgical method than to filler