Philtrum-to-lower-third ratio

The philtrum occupies the skin interval between the nose and upper lip. Its share of the lower third shows how much of the nose-to-chin distance passes before the lips begin. The remaining height contains the visible lips and the chin region below them.

Because this is a share, total lower-face height affects the result. An ordinary philtrum can occupy a large fraction of a short lower face. The same interval becomes a smaller fraction when more height is added below the mouth.

Lengthening the philtrum while the lips and chin intervals stay similar raises its share. The upper lip moves farther beneath the nose, making the intervening skin more visible. More of the lower face is used above the mouth.

Shortening the region below the lips also raises the share while leaving the philtrum unchanged. The mouth may then sit close to the chin because there is little height beneath it. This creates a different appearance from a physically long nose-to-lip interval.

A high share within a long lower face can still leave substantial height for the lips and chin. Compare the full nose-to-chin distance before concluding that the lower region is cramped.

A short philtrum places the upper lip close beneath the nose and lowers its share of the lower face. The nose and mouth form a compact pair, while the remaining space lies within the lips and chin.

Extra height below the mouth can produce the same low share without shortening the philtrum. The lip border sits high within the lower third because the bottom of the face is farther away. A long, narrow chin in this arrangement can make the lower face look elongated despite the low philtrum percentage.

Chin-to-philtrum ratio compares the interval below the lower lip with the interval above the upper lip. It helps locate whether a low philtrum share accompanies more height at the chin. Chin width then determines whether that height forms a broad base or a slender ending.

The ratios are not exact inverses because the full lower third includes the visible lips, while chin-to-philtrum leaves them out. Taller lips can occupy more of the total even if the surrounding skin intervals stay the same.

Nasal height adds context above the philtrum. A short nose followed by a long philtrum may place the upper lip at a similar level to a tall nose followed by a short philtrum. The total eye-to-lip distance can match while the spacing immediately above the mouth differs.

The central groove and raised columns give the philtrum a visible surface shape. A flatter region can look like a longer uninterrupted area of skin even when its upper and lower endpoints remain fixed.

Nunes and Bran tested altered philtral contours in paired female portraits. Respondents generally preferred defined contours, and removing them made the upper-lip region appear longer and the face older to many observers. The study changed contour, not philtrum height.

As the lower face develops, added height below the mouth can reduce the philtrum's share without shortening the philtrum itself. Ferrario and colleagues documented substantial lower-face growth towards adulthood. The ratio changes according to how that growth is distributed.

In adulthood, reduced visible lip height and changes in philtral contour may make the skin above the mouth more conspicuous. Sforza's lip measurements and Nunes and Bran's contour experiment describe different contributions to that appearance. Comparable earlier photographs help distinguish a longstanding allocation from a later change.

The 18–24% reference places the upper-lip border around the upper fifth of the nose-to-chin distance. It illustrates vertical placement rather than a preferred interval established for every lower-face shape.

Naini and colleagues found tolerance across a range of chin heights in their experiment. Changing chin height also changes the philtrum's percentage of the lower third, although the philtrum itself stays fixed.