Nathan Hamilton, Logan Park High School, Dunedin, asks :-

Why do I have a dimple in my chin?

Kirk Hamilton, a physiologist at Otago University responded.

As we look at people, we notice interesting characteristics about one another. We might see a person with blonde hair, hazel eyes or even a dimple in the chin. I would bet we have all noticed people who have a prominent chin dimple. As I think about well-known celebrities who have dimples in their chins, a number of names come to mind quickly: Adele, Sr. Ian McKellan, Gwyneth Paltrow, Ben Affleck, John Travolta, Kirk Douglas (Michael Douglas’ father) to name a few.

There is an old proverb that states that ‘A dimple in the chin, the devil within’. I am not sure about that, however, from appearance, the dimple (chin cleft) is an indentation on the surface of the chin and it can be circular or Y-shaped, for example. The underlying form of the dimple is the result the anatomy of the lower jaw bone, the mandible. The mandible is composed of two parts that are joined in the middle. Sometimes, the two halves of the mandible do not fuse properly at the center point in the region of the chin during embryonic development. This misalignment allows the formation of a groove in the tissues of the chin that can be deep enough to reach the mandible, resulting in the dimple.

The chin dimple is a dominant inherited trait in humans, which means if both parents have dimples then their children should also have dimples. I do say ‘should’ because even if a trait is ‘dominant’ it is not 100% certain. There are situations where the gene responsible for this dimpling trait might be affected; and this is described in science as variable penetrance. Variable penetrance means that even though the inherited trait for the chin dimple is dominant, the dimple might not be formed because of another factor such as something environmental or modifier genes that influence the development of the mandible during the development of the baby before birth.

Some people believe that dimples are beautiful. In fact, it is now fashionable to have ‘designer dimple’ plastic surgery known as ‘dimpleplasty’. There are a couple of techniques that can be used to ‘create’ a dimple and this it is considered a minor procedure that is performed by a surgeon under local anesthesia. So, for those of us who have a chin dimple, we should feel lucky! And, if you were wondering, yes, I was named after a famous dimpled actor, Kirk Douglas, but my dimple is almost always covered with a goatee!