Lip and Philtrum Anatomy: Why Natural Lip Results Start With Diagnosis

A 2025 review by a team of Korean and international anatomists and clinicians looks at how the lips and the area above them (the philtrum) are built, how they change with age, and how that should shape lip filler treatment. Its central message is that natural-looking results depend less on how much product is used and more on understanding each person's own lip structure first.

Why this was written

Lip treatment has shifted over the past decade. Early approaches focused mostly on adding volume. The authors argue that the field is moving toward restoring shape and definition instead: the border of the lip, the soft ridge just above it, the curve of the upper lip known as the Cupid's bow, the two vertical columns of the philtrum, and the corners of the mouth.

To do that well, an injector needs a mental map of what lies under the surface. This review pulls together anatomy research and clinical experience into one place.

What the review describes

The lip has several thin layers. Under the skin and the red part of the lip there is very little fat, then the ring-shaped muscle that closes the mouth. The main arteries of the lips run deeper, close to the inner lining. The authors point out that these arteries are only about a millimetre wide and that their branching pattern is symmetrical in only about half of people. In other words, two lips that look alike can have quite different plumbing underneath.

The review also lists typical ageing changes. Over time, both lips tend to become thinner and longer, the Cupid's bow loses definition, the philtral columns flatten, the skin between the nose and lip lengthens, and the corners of the mouth turn down. Not everyone has all of these, and the right treatment depends on which ones are present.

The paper notes a validated five-point lip fullness scale that clinicians can use to describe lips consistently, with a one-point change considered clinically meaningful. Tools like this help a clinician and patient talk about goals in shared terms.

Proportions are not one-size-fits-all

One of the more useful parts of the review for patients is its discussion of proportions. A commonly quoted "ideal" upper-to-lower lip ratio is roughly 1 to 1.6, but the authors show that preferred ratios differ by ethnic background and culture, and that preferences have shifted over time. Mouth width and lip projection also vary between populations.

The practical point is that there is no single correct lip. A plan should be built around your own face, background and wishes, not a template or a social media trend. Our article on balancing uneven lips looks at how small asymmetries are approached.

Safety points the review highlights

Because the lip arteries run in predictable layers, the authors describe which depths are considered higher risk and recommend staying away from them. They suggest modest volumes, generally up to about 1 millilitre per lip in a session, and note that some swelling settles over the first one to two weeks. They also describe staging treatment two to four weeks apart when more change is wanted, rather than doing everything at once.

The review reminds clinicians to watch for skin blanching or a lace-like discolouration, which can signal reduced blood flow and calls for prompt treatment with hyaluronidase. Our article on vascular occlusion safety explains this in more detail.

Product choice matters too. The authors favour hyaluronic acid fillers of moderate firmness for the lips, because the area moves constantly and needs a soft, flexible result. A key safety advantage of hyaluronic acid is that it can be dissolved if needed.

How strong is this evidence?

This is a narrative review: experienced authors summarizing anatomy studies, earlier clinical research and their own approach. It is valuable for teaching and for shaping good habits, but it is not a trial and does not compare techniques head to head. Several measurements quoted come from specific populations, so they may not apply exactly to people in Cape Breton. The studies it cites on lip outcomes were mostly small with short follow-up.

What it means for you

• Assessment comes first. A good lip consultation looks at your lips at rest and when you talk and smile, your philtrum, your teeth and chin, and the rest of your face.
• Shape over size. Many people are happier with subtle restoration of definition than with a large increase in volume.
• Staging is normal. Treating in smaller steps can allow swelling to settle and lets you decide whether you want more.
• No treatment is also an option. Some concerns, such as fine lines or dryness, may be better addressed with skincare or other approaches.

People who should wait or avoid lip filler include those who are pregnant or breastfeeding, have an active cold sore or infection near the mouth, or have certain allergies or medical conditions. Common side effects include swelling, bruising, tenderness and lumps, and uncommon risks include infection and blood-vessel blockage.

Frequently asked questions

Why does my injector look at my teeth and chin for a lip treatment?

The lips sit on the teeth and are framed by the nose and chin. How much the upper lip shows over the teeth, and how the lips sit in profile, affects what will look balanced.

Can lip filler make the philtrum shorter?

Filler can sometimes add subtle support to the philtral columns and lip border, but it cannot truly shorten a long upper lip. Your consultation should cover what is realistic.

Is there a standard amount of filler for lips?

No. The review gives general ranges, but the right amount depends on your anatomy and goals, and less is often enough.

If you are considering lip treatment, HealthPark offers consultations where we look at your lip anatomy and goals together before discussing options. You can also read our lip filler guide for an overview.

Source

Hong GW, Choi W, Yoon SE, Wan J, Yi KH. Anatomical-based diagnosis and filler injection techniques: lips and philtrum. Life, 2025. Read the study