In origin “jowls” is as a word related to Middle English chauel (jaw), and cholle (meaning neck from which the word “collar” is derived). But cholle was also used to indicate the “head” so the derivative “jowl” has different meanings when applied to different beasts and circumstances – it can mean the head of a fish, the “dewlap” fold at the center of a cow’s neck, and in humans it is generally applied to a fold of skin hanging at the side, and below the level, of the lower jaw (mandible).
The general shape of the face is determined by the underlying skeletal structure – the bones. Overlying the bone is a sheet of muscle, which although the anatomists think of the many individual muscles that comprise this sheet, the surgeon thinks of as the “superficial muscle aponeurotic system,” more conveniently shortened to SMAS.
Superficial to the SMAS is a layer of fibro-fatty tissue which separates it from the skin. All of this can be verified by holding the cheek between the thumb in the mouth and the fingers outside it; if the muscle of the cheek (buccinator) is contracted, the skin can still be readily moved over it. It is a loose attachment of the skin by collagenous fibers to the underlying muscle fascia that keeps it in place although permitting it to be stretched and slightly displaced. There are persons born with abnormal defects in their collagen, and in such unfortunates it is possible to pick up the skin of the face in a fold and draw it away from the skull.
As one ages, the collagenous tissue becomes thinned and weakened. If one never stood erect, the skin would remain in place, as it does in ageing persons who are paralysed. But for those fortunate enough not to be paralysed, gravity acts on the skin drawing it downwards – take one of those death defying rides or loop the loop and you feel the skin on your face pulled out of place by the forces of gravity. It is all the more likely to sag below the level of the jaw (that is, form jowls) in persons with damaged collagen due to excess exposure to ultra-violet light, natural or artificial, and in those with heavy pads of fatty tissue in the face.