The aging changes seen in the lower third of the face affect the lips, chin, lower cheeks, and neck. Changes result from a combination of chronic ultraviolet light damage to the skin, loss of subcutaneous fat, changes due to the muscles of facial expression, gravitational changes from loss of elasticity of the tissue, and remodeling of the underlying bony and cartilaginous structures.
Changes in dentition and absorption of maxillary and mandibular bone may result in an overall loss of height and volume. The chin rotates forward and is seen to sharpen and protrude. These changes may result in the lower third of the face appearing smaller relative to the upper and middle thirds, straying from the ideal, approximately equal proportions. Aging changes from the middle third of the face may contribute to this appearance, as nasal tip ptosis may create the appearance of a shortened upper lip. The constant effects of gravity combined with loss of elasticity in the tissue may allow for excess skin to droop off the mandible, manifesting as ‘jowls’ along the mandibular rim and ‘wattles’ in the anterior neck.
The origin of the melolabial fold is unclear. Some authors feel that it is derived from insertions of lip elevator muscles into the skin, whereas others hypothesize that it results from differences in the subcutaneous structure in the cheek and oral areas. In any case, the prominence of this fold varies with age. In childhood, the lips and cheeks contain more abundant subcutaneous tissue, such that this fold is inapparent; however, age-related loss of subcutaneous fat, combined with the loss of elasticity of the skin, results in the draping of redundant tissue over the muscular insertion point into the groove. Clinically, this results in an apparent deepening of the melolabial fold.
Wrinkles form around the lips as a result of the constant pulling of the orbicularis oris muscle on progressively more inelastic upper- and lower-lip skin, creating angular, radial, and vertical wrinkles. Marionette lines may form as vertical wrinkles extending downwards from the oral commissures. The effects of gravity result in drooping of the oral commissures laterally and downward, which may lead to a tired and sad appearance. Loss of elasticity may lead to lip skin redundancy, enhancing the drooping and vertical elongation. Fullness of the lips and a strong definition of the philtrum are seen in youth; however with advancing age there is atrophy of the orbicularis oris muscle and loss of subcutaneous tissue, leading to an overall flattening and loss of fullness in the lips, with less of the vermillion showing. ‘Cupid’s bow’, the central arch of the upper lip, may flatten. In severe cases, there may be disruption of normal lip position. Loss of subcutaneous tissue and hypotonic lip musculature may allow the lips to invert, creating a ’sucked-in’ appearance; however the occasional patient may develop a lip ectropion due to excess tissue and hypotonic lip musculature.