Why does the nasolabial line (smile line) form?
The nasolabial line is the natural boundary between the cheek tissue and the upper lip, and it is seen when smiling even in young people. With age, loss of deep fat in the midface, downward and forward shift of superficial fat, reduced bony support beside the nose and loss of skin elasticity make the line noticeable even when the face is at rest.
The smile line forms where the soft tissue of the cheek meets the upper lip. At this boundary lie close attachments to the skin of the facial muscles that lift the upper lip, and connective tissue structures that help hold the cheek in place. The cheek tissue above the line is relatively mobile and full, while the lip area below it is more fixed. Because the cheek moves upwards and outwards when smiling, this boundary becomes prominent as a crease. The length, depth and shape of the line vary from person to person. The nasolabial line is therefore a normal facial feature that is seen in children and young people too when they smile. What is bothersome aesthetically is not the line itself but its appearing as a deep shadow when the face is at rest.
With age, the deep fat compartments of the midface become thinner, support in the cheekbone area decreases, and the superficial fat, together with looseness of the connective tissue, descends somewhat. This tissue, collecting just above the line, makes the crease look deeper. Bone loss in the upper jaw over time, especially beside the nose, can also reduce support for the upper lip and the base of the nose. Loss of collagen and elasticity in the skin, sun damage, smoking, marked weight loss and inherited facial structure all contribute to these changes. In some people, what stands out is not the line itself but the heaviness of the tissue above it. The depth and cause of the smile line can therefore be quite different in two people of the same age.
Is the problem the line itself, or midface support?
In many people the deepening of the smile line relates less to the line itself than to loss of support in the midface. In that case, filling only the line can make the area around the mouth look heavier; cheekbone and midface support can give a more balanced result. In people whose midface support is adequate but whose line remains prominent, direct filler to the line can be considered.
At the consultation the face is examined from the front and the side, at rest and while smiling. The forward projection of the cheekbone, the transition between the under-eye area and the cheek, whether tissue has gathered above the line and how deep the part of the line near the side of the nose is are all assessed. Looking at how the face changes when sitting up and lying down can also help. If needed, your older photographs help in understanding what has changed in your face over time. A common misconception is to think of the line as a deep trench and try to fill it completely. If there is descended tissue above the line, though, volume added to the line can push the area around the mouth forward rather than lift that tissue. The assessment is therefore made by looking at the whole midface, not only at the line.
In midface support, the aim is to counterbalance the reduced structural support by placing measured amounts of hyaluronic acid at specific support points in the cheekbone area. In some people this approach can indirectly soften the shadow of the smile line; however, the size of the effect varies from person to person and it does not remove the line on its own. In people who have no marked midface volume loss and whose cheekbones are already full, adding filler to the cheekbone can widen the face unnecessarily. In many cases a measured combination of the two approaches is planned: midface support is assessed first, and any remaining line is then treated with a small amount of direct filler if needed. Details of cheek filler and the general mechanism of facial sagging are covered on the relevant pages.
When and how is direct filler placed in the smile line?
Direct nasolabial filler is considered when the line remains prominent despite adequate midface support, or when the upper part of the line near the side of the nose is deep. Usually a small amount is placed as deep support in the area beside the base of the nose, and with a medium-density gel in a more superficial layer along the line.
The upper part of the line, near the side of the nose, corresponds to an area where support from the underlying bone has decreased. Measured support in the deep layer here can soften the transition between the base of the nose and the upper lip. In the middle and lower parts of the line, filler is placed in small amounts under the skin with a fine needle or a blunt-tipped cannula, depending on the anatomy of the area. Medium-density products that can move with the area are generally preferred here. The clinical studies and approved uses of many hyaluronic acid fillers include moderate to deep facial folds, particularly the nasolabial fold. Which product is used depends on the thickness of the tissue and the depth of the line.
The nasolabial area is one of the areas that need care in terms of blood vessels. The facial artery runs upwards around the corner of the mouth and continues beside the side of the nose as the angular artery; the course of this vessel can vary from person to person. For this reason, treatments beside the side of the nose are carried out with particular caution; choice of layer, slow injection, low pressure and progressing in small amounts are part of safety. Before treatment you are asked about earlier procedures, the medicines you take and your allergy history; the area is cleaned with antiseptic, and the lidocaine present in many products reduces discomfort. The procedure often takes 20–40 minutes. A few days of mild swelling, tenderness and bruising may follow; the final look is usually assessed within two to four weeks, and the review visit is planned accordingly.
Does nasolabial filler look natural, and how is overfilling avoided?
Nasolabial filler can look natural when the aim is to soften the line and a measured amount is used. Trying to erase the line completely, on the other hand, can lead to a bulge when smiling, forward fullness around the mouth and a heavy look. Progressing gradually, assessing the smiling movement and reviewing again at a follow-up help keep it natural.
The smile line is part of the facial expression; it is natural for it to become more prominent when smiling. If too much product is used to flatten a line that looks deep at rest, the cheek tissue rides over that volume when smiling, and an unnatural bulge can form above the line. This look, in which the area around the mouth projects forward and the upper lip area feels heavy, is one of the common causes of an overfilled appearance. Adding product to the same line again and again over the years can also lead to filler building up and shifting over time. Such build-up can be reduced with hyaluronidase when necessary, but preventing it is easier than correcting it afterwards. The measure of naturalness is therefore not the line being invisible but the face looking balanced in motion too.
Steps that help a natural result include starting with a measured amount, assessing midface support first, checking the face both at rest and while smiling during treatment, and making the final assessment after swelling has settled. In the first days, swelling can make the line look as if it has disappeared completely; this is temporary. A slight difference between the two sides is natural; aiming for exact symmetry can lead to too much product being used. At the review visit a small top-up can be given if needed, and if it is not needed, no extra treatment is given. Medical record photographs taken under standard conditions help the change to be assessed objectively. General principles for keeping a natural look are covered on the natural results page.
What options are there for smile lines besides filler?
Depending on the cause of the line, hyaluronic acid filler to the midface, biostimulators for more widespread volume loss and skin quality, device treatments for mild laxity and skin-quality treatments for superficial wrinkles can be considered. In marked sagging, non-surgical methods have limited effect and a surgical assessment may come up.
Biostimulators such as calcium hydroxylapatite or poly-L-lactic acid aim, in people with more widespread midface volume loss and skin thinning, at a gradual change by supporting the tissue’s own collagen response; their effects appear over weeks and they are not dissolved by hyaluronidase. Device treatments such as focused ultrasound or radiofrequency may be considered for tightening in mild to moderate tissue laxity; they do not add volume. Treatments aimed at skin quality, such as salmon DNA, skin boosters or mesotherapy, can help with fine lines around the smile line and skin texture, but they do not correct a deep crease. These methods are often complements rather than alternatives to each other. Knowing which method addresses which problem helps keep expectations realistic.
Botulinum toxin is generally not considered a first option for the smile line; treating the muscles that lift the upper lip in this area can affect the smile and lip movement. In selected situations such as a gummy smile, a very low dose may be given to these muscles, but the aim is not to correct the smile line. When botulinum toxin and filler are each considered is covered on the page comparing botox and filler. In people with marked sagging of the cheek and jawline, excess skin or very deep creases, filler or other non-surgical methods may not provide the expected change; in that case, referral for surgical facelift options may be made. Which approach or which combination is suitable is decided at the consultation by assessing your facial structure and expectations together.
Who may not be suitable for nasolabial filler, and what are the risks?
Treatment is generally not given, or is postponed, during pregnancy and breastfeeding, with an active cold sore or infection around the mouth, with a known allergy to the filler’s contents and in some autoimmune conditions. Common side effects are swelling, bruising and tenderness; rare but important risks include vascular occlusion, infection and delayed inflammatory reactions.
The area around the mouth is a common site for the cold sore virus; if you often get cold sores, it is important to tell your doctor. Blood-thinning medication can increase the likelihood of bruising; do not stop your medicines yourself without consulting the doctor who prescribed them. Recent dental treatment can also affect timing. If an important event is approaching, it is easier to plan treatment a few weeks in advance to allow for possible swelling and bruising. If a non-degradable material such as silicone, or a filler of unknown content, has previously been placed in this area, a detailed assessment is needed before a new treatment. In people with marked sagging who expect a facelift-like result from filler, the doctor explains the limits of filler clearly and may in some cases advise against treatment.
Mild swelling, bruising and tenderness to touch usually ease within a few days. By contrast, increasing pain after treatment, blanching of the skin, a net-like purplish discolouration, colour change at the side of the nose or the upper lip, or any change in vision is not part of normal healing. These signs may suggest vascular occlusion and call for contacting the treating doctor or an emergency department without delay. The availability of hyaluronidase is a general safety measure that allows hyaluronic acid filler to be dissolved quickly when necessary. Painful swelling or red lumps appearing weeks later should also be assessed. Sharing the product name and date of your earlier treatments helps the plan to be made safely.
Frequently asked questions
How long does smile line filler last?
Hyaluronic acid filler in the smile line often stays noticeable for 6–12 months, and this can be longer depending on the product and amount used. Because the area moves constantly with speaking and smiling, duration is generally shorter than in less mobile areas such as the cheekbone or chin. Filler in the cheekbone for midface support often lasts longer.
Does the line disappear completely after nasolabial filler?
Generally not, and that is not the aim; the smile line is a natural crease of the face and it is normal for it to show when smiling. The purpose of filler is to soften the deep shadow seen when the face is at rest. Using too much product to erase the line completely can create a bulge and a heavy look when smiling; a more balanced result is aimed for with a measured amount.
Will nasolabial filler change my smile?
Filler in a measured amount and in the right layer does not markedly change the smile. In the first days, swelling may cause a slight feeling of tightness or fullness when smiling; this usually eases within a week or two. Too much filler, on the other hand, can create a bulge above the line when smiling; if you notice a difference that does not go away, it should be assessed at a review.
At what age do smile lines start to become more noticeable?
There is no single age; in many people the smile line begins to be noticed at rest in their thirties and forties. Facial structure, heredity, weight change, sun damage and smoking can bring this forward or delay it. In young people a line seen only when smiling is normal and is not in itself a reason for treatment.
One of my smile lines is deeper than the other; can this be corrected?
Often yes; a difference between the two sides can be balanced by planning different amounts of product for each side. It is natural for the two halves of the face to differ a little; bone structure, chewing habits and always sleeping on the same side can contribute. The aim is not exact symmetry but for the two sides to look balanced; the cause of the asymmetry is assessed at the examination.
Do tooth loss or dentures affect the smile line?
They can; the teeth and jawbone support the upper lip and the area around the mouth. Bone loss developing after tooth loss, or a poorly fitting denture, can contribute to the area around the mouth sinking inwards and lines becoming more marked. In that case, an assessment by a dentist may be advised before filler; filler placed without correcting dental support may not give the expected result.
What is the difference between nasolabial filler and a liquid facelift?
Nasolabial filler is a regional treatment that targets a single crease or the points supporting it. A liquid facelift is a more comprehensive approach in which several areas, such as the midface, jawline and temple, are planned with filler, biostimulators and sometimes botulinum toxin. If the cause of the smile line is widespread loss of support, a broader plan may be discussed.
What should I look out for in the first days after nasolabial filler?
In the first days it is generally advised to avoid positions that press on the face, massage of the area, intense exercise, saunas and alcohol. A cold compress may help reduce swelling; if you are planning dental treatment soon, discuss this with your doctor. Increasing pain, blanching of the skin or a net-like purplish discolouration should be reported to a doctor without delay.
Sources (3)
- U.S. FDA: RESTYLANE INJECTABLE GEL, P040024 (Premarket Approval record) (2005)
- U.S. FDA: JUVEDERM 24HV, JUVEDERM 30 and JUVEDERM 30HV Gel Implants, P050047 (Premarket Approval record) (2006)
- Ghaddaf AA et al. (J Cosmet Dermatol): Monophasic versus biphasic hyaluronic acid filler for correcting nasolabial folds: a systematic review and meta-analysis (2022)
This content is for general information and does not replace a personal medical assessment.