Ron Sheppard of Fielding asks :-

Why do we have a philtrum, the indentation on our upper lip below the nose, and is it true that the Greeks considered it an erogenous zone?

George Dias, an anatomist at the Otago Medical School, responded.

There is no direct explanation for the presence of the `philtrum' in the anatomical literature.

Philtrum - A philter or love potion (Latin - philtron - a love-charm, depression on upper lip - from Greek - phileo to love), Its anatomical term is the infranasal depression; the groove in the midline of the upper lip

Regarding this being an erogenous zone: there is no anatomical specialisation to make the sensory nerve supply to this region different to the rest of the upper lip. Therefore, it is no more sensitive than other parts of the upper lip.

The junction between external hair-bearing skin and the red hairless surface of the upper lip almost invariably takes the form of the double-curved 'Cupid's bow'; (centrally convex downwards) then bilaterally rapidly rising to an apex corresponding to the lower end of each ridge of the philtrum.

The muscle within the lips, which enables us to 'purse our lips' (orbicularis oris [around the mouth] muscle) in the upper lip has fibres from the right and left, which meet, interlace and overlap beneath the hollow of the philtrum. When our lips are `pursed', reducing the size of the mouth opening, the philtral hollow becomes more prominent.

In foetal development of the face, the philtrum is formed by the 'fronto-nasal prominence' and the rest of the upper lip is formed by left and right 'maxillary prominences'.

The area of the philtrum is formed by the fused medial nasal prominences.