Why the face ages: fat, ligaments, and bone

Sagging is not just due to gravity

In the past, facial aging was seen as the result of gravity constantly pulling the skin and the fat beneath it downward, and facial fat was also thought to be one continuous layer of tissue ^[1]. As research accumulated over the past 40 years, a proposal made in 1965, that changes in the muscles and bones, not just the skin and fat, are involved in facial aging, was confirmed and explored in greater depth ^[1].

The face is built from overlapping layers of bone, ligaments, muscle, fat, and skin, and aging takes place in all of these layers ^[2]. Aging is described as a process with many causes, in which factors within the body (intrinsic factors) and factors in the outside environment (extrinsic factors) act together ^[5]. This is why the face can change differently from person to person, even at the same age.

Fat: divided into separate compartments

Researchers have shown that facial fat is not a single sheet but is divided into several compartments (fat compartments) across the whole face, and this discovery led to advances in facial rejuvenation techniques ^[1]. The fat compartments are divided into superficial compartments close to the skin and deep compartments beneath them, and the deep compartments provide structural support for the midface and the superficial compartments ^[5].

Each compartment is an independent unit separated by boundaries of connective tissue (fascia), and its volume changes with age ^[3]. In particular, the deep inner cheek compartment, the compartment around the nasolabial fold, the superficial middle cheek compartment, and the outer cheek compartment are cited as areas that hollow out more noticeably than the others ^[3]. Based on this kind of map, it has become possible to selectively fill the compartments that have lost volume ^[3].

Ligaments: the structures that hold the face in place

Retaining ligaments are fibrous tissues that anchor the skin and soft tissue to deeper structures. These ligaments are described as important structures for understanding facial aging and rejuvenation ^[6]. They divide the spaces and compartments of the face at consistent anatomical locations, and the parts that extend toward the skin form partitions between the fat compartments ^[6].

The literature explains that as the support from the ligaments decreases with age, the soft tissue above them becomes loose ^[4]. In surgery, it is important to release the appropriate ligaments according to the desired result, and because the ligaments also serve as landmarks indicating the location of the facial nerve branches, they are used as a guide to avoid nerve injury ^[6]. However, the classification and naming of the ligaments have been described differently in the literature because of differing interpretations of the anatomy ^[6].

Bone: a shrinking skeleton and changing contours

The facial bones also change considerably with age, and resorption is described as especially prominent in the parts of the jawbone associated with the teeth ^[4]. When the projection of the skeleton decreases, it gives the impression that the face has moved downward ^[4].

Aging changes take place in every layer between the skin and the bone, but how much each layer contributes to the overall change in appearance has not yet been fully established ^[4]. This is why it is difficult to explain the changes in the face by any single cause.

The mouth area is where many changes overlap

The area around the mouth is strongly affected by aging ^[7]. The literature notes that sun exposure, bone resorption, repeated contraction of the muscles around the mouth, gravity, changes in the skin tissue, and unhealthy lifestyle habits all act together ^[7]. Typical changes include the following ^[7].

• Fine lines on the lips
• Deeper smile lines (nasolabial folds) and lines below the lips
• A longer, flatter upper lip
• Drooping corners of the mouth and lines below them (marionette lines)
• Less of the red part of the lips showing and less of the upper teeth showing
• An uneven, bumpy chin

Understanding how aging works changes the treatment plan

The understanding that aging takes place in several layers is also reflected in treatment planning. One review described an approach that first restores the volume of fat compartments that have shrunk and then addresses the laxity of the superficial musculoaponeurotic system (SMAS) and skin above them ^[3]. It stated that volume restoration is sometimes used on its own in appropriate patients, but is usually used to complement a facelift ^[3].

When fillers are used, it is also stressed that understanding the anatomy and biomechanics of the face is necessary to achieve natural results and reduce the risk of adverse reactions ^[8]. An algorithm for choosing treatment methods based on how the fat compartments change with age has also been proposed ^[5]. However, most of the sources reviewed here are reviews summarizing anatomy and the authors' experience, so they are difficult to treat as evidence comparing the effectiveness of specific treatments.

It should also be taken into account that when aging begins and how fast it progresses differ between ethnic groups ^[2]. Which changes are most prominent in which layer differs from person to person, so an individual assessment through an examination is needed.