The philtrum (Latin: philtrum, Greek: φίλτρον philtron, lit. "love charm"), or medial cleft, is a vertical groove in the middle area of the upper lip, common to many mammals, extending in humans from the nasal septum to the tubercle of the upper lip. Together with a glandular rhinarium and slit-like nostrils, it is believed] to constitute the primitive condition for mammals in general.

In most mammals, the philtrum is a narrow groove that may carry dissolved odorants from the rhinarium or nose pad to the vomeronasal ***** via ducts inside the mouth.

For humans and most primates, the philtrum survives only as a vestigial medial depression between the nose and upper lip.

The human philtrum, bordered by ridges, also is known as the infranasal depression, but has no apparent function. That may be because most higher primates rely more on vision than on smell. Strepsirrhine primates, such as lemurs, still retain the philtrum and the rhinarium, unlike monkeys and apes.

In Jewish mythology, each embryo has an angel teaching them all of the wisdom in the world while they are in utero. The Angel lightly taps an infant's upper lip before birth, to silence the infant from telling all the secrets in the universe to the humans who reside in it; the infant then somewhat forgets the Torah they have been taught. Some believers of the myth speculate that this is the cause of the philtrum, but it does not have a basis in traditional Jewish texts.

In Philippine mythology the enchanted creature diwata (or encantado) has smooth skin, with no wrinkles even at the joints, and no philtrum.

In Key Largo (1948), Frank McCloud (Humphrey Bogart) tells a fairy tale to a child, saying that, before birth, the soul knows all the secrets of heaven, but at birth an angel presses a fingertip just above one's lip, which seals us to silence.

In the movie Mr. Nobody, unborn infants are said to have knowledge of all past and future events. As an unborn infant is about to be sent to its mother, the "Angels of Oblivion" lightly tap its upper lip, whereupon the unborn infant forgets everything it knows. The movie follows the life story of one infant, whose lip hadn't been tapped.

In the movie The Prophecy, the Archangel Gabriel (Christopher Walken) asks Thomas Dagget, "Do you know how you got that dent in your top lip? Way back, before you were born, I told you a secret, then I put my finger there and I said 'Shhhhh!'"

In Action Comics #719 the Joker says a clue is right under Batman's nose. This leads him to a Dr. Philip Drum..

In the book Prince Ombra by Roderick MacLeish, the "cleft on our upper lips" is attributed to being hushed by a "cavern angel" just before we are born.