The layers of the face — Organisation, continuities and the plane of dissection
The concentric five-layer arrangement and its constancy throughout the cervicofacial territory, the differential behaviour of fixed and mobile SMAS, the anatomical revision of the deep layers and the plane of dissection that follows from it.
Content intended for healthcare professionals. It does not replace clinical assessment and is not written as patient information.
Key points
- The cervicofacial territory maintains a constant organisation in five concentric layers. Each layer changes name by region, but not its relative position.
- The layers glide over one another where areolar tissue permits, and remain united where the retaining ligaments fix them. Distinguishing the two situations underlies all rejuvenation surgery.
- The SMAS comprises two portions with distinct behaviour: one fixed over the parotid gland, which tends to atrophy, and one mobile anterior to it, which descends and shifts medially.
- Recent anatomical work has modified the description of the deep layers: they form not a lamina but a three-dimensional fascia of fibrofatty nature, through whose thickness the nerves run.
- The working plane follows from that arrangement: immediately deep to layer 3 and superficial to the deep fascia, without seeking planes within its thickness.
A constant arrangement
The face and neck are organised in five concentric layers arranged from the surface inwards. Their surgical interest lies not in the description itself but in one notable property: the order is maintained throughout the cervicofacial territory. A single layer takes different names according to the region examined — galea in the forehead, temporoparietal fascia in the temple, SMAS in the cheek, platysma in the neck — but always occupies the same position relative to the others. That constancy allows the operating plane to be recognised at any point of the dissection, without relying on estimated depth.
The five layers
Layer 1 comprises the skin and subcutaneous tissue. Layer 2 corresponds to the hypodermis, traversed by the retaining ligaments and organised into superficial fat compartments. Layer 3 is the musculoaponeurotic layer: the SMAS and the mimetic muscles that form part of it, among them the orbicularis oculi and the platysma. Layer 4 consists of loose areolar tissue and houses the deep fat compartments. Layer 5 is the deep fascia and the underlying periosteum. One asymmetry between them is worth retaining from the outset: layers 1 to 3 are mobilised in surgery; layers 4 and 5 constitute the floor on which one works and house the structures that must be preserved.
Function of each layer and its involution with age
| Layer | Function | Involution with age |
|---|---|---|
| 1. Skin and subcutis | Coverage, colour and surface texture | Solar elastosis and static rhytids. Loss of elasticity limits the redraping that can be achieved |
| 2. Hypodermis and superficial compartments | Gives the surface its form and transmits muscular movement to the skin through its septa | Medial displacement and accumulation above the ligaments, the mechanism from which the facial sulci derive |
| 3. SMAS and mimetic muscles | Structural support and transmission of movement. This is the layer that is mobilised and repositioned | Loss of support: the fixed portion atrophies and the mobile portion descends |
| 4. Areolar tissue and deep compartments | Provides volume and allows the musculature to glide over the deep plane | Atrophy of the fat content, directly responsible for malar and periorbital hollowing |
| 5. Deep fascia and periosteum | Contains and protects nerves, vessels and glands. It constitutes the deep limit of the dissection | Resorption of the underlying skeleton, with loss of the support on which the superficial layers rest |
The clinical reading of the table above is that facial ageing does not obey a single mechanism. Layer 1 loses quality, layer 2 is displaced, layer 3 loses support, layer 4 atrophies and layer 5 resorbs. A procedure acting on only one of them will correct only its corresponding component, which explains why volume restoration and tissue repositioning are complementary rather than alternative manoeuvres.
The SMAS: limits and continuities
The superficial musculoaponeurotic system invests the parotid gland and the facial musculature, and constitutes layer 3 in the cheek region. Its continuities define its true extent: cranially it continues with the superficial temporal fascia and the galea aponeurotica; caudally, with the platysma; and anteriorly, with the deep fat compartments. Its anterior limits are well established: superiorly, the zygomaticus major muscle and the zygomatic ligament; inferiorly, the mandibular ligament, already in platysmal territory. That uninterrupted craniocaudal continuity is what allows a single composite flap to be raised from the temporal region to the neck, and what explains why traction correctly applied to the cheek is transmitted to the cervicomental angle.
Two portions with distinct behaviour
The SMAS does not behave homogeneously throughout its extent, and that heterogeneity has direct technical consequences. The fixed portion rests on the parotid gland, firmly adherent to the parotid fascia. The mobile portion lies medial to the gland, extending to the zygomaticus major muscle and retained by the orbicular, zygomatic, masseteric and mandibular ligaments. The two age differently and produce different clinical signs, as the following table summarises.
| Fixed SMAS | Mobile SMAS | |
|---|---|---|
| Location | Over the parotid gland | Medial to the gland, as far as the zygomaticus major |
| Fixation | The parotid fascia | The orbicular, zygomatic, masseteric and mandibular ligaments |
| Involution | Progressive atrophy, with a lateral concavity appearing | Medial displacement together with the superficial fat compartments |
| Clinical expression | Lateral hollowing of the cheek | The facial sulci, as gliding is arrested against the ligaments |
The technical consequence
If the presenting sign — the sulcus — originates in the mobile portion retained by its ligaments, dissecting and tractioning the fixed portion will not correct it while those ligaments remain intact: the segment that was not the problem is mobilised while the one that was remains anchored. Hence the invariable sequence: the ligaments are released first, traction follows. From the same principle it follows why simple plication of the SMAS upon itself, without prior opening or release, gives acceptable short-term results and fails to maintain them: tension falls on the skin, whose elasticity eventually yields.
The revision of the deep layers
The classical description presents layer 4 as loose areolar tissue and layer 5 as a fascial lamina followed by periosteum, thereby implying a cleavage plane between them. Recent anatomical studies do not confirm that separation: layers 4 and 5 are not histologically dissociable and in fact constitute a single structure, a three-dimensional deep fascia of fibrofatty nature, organised into superficial and deep sheets that include the superficial sheet proper, the muscular fascia, the glandular capsule and the carotid sheath.
Why that revision matters in theatre
The consequence follows from a single anatomical fact: the nerves run within the thickness of that fascia, not beneath it. Seeking a plane inside the deep fascia does not constitute a deeper and therefore safer dissection, but precisely the manoeuvre that exposes the facial nerve to injury. From this the limit of the working plane follows: immediately deep to layer 3 and superficial to the fascia, without advancing into its thickness. A qualification about the deep fat compartments is worth adding, since the classical description attributed them to the SMAS: with the exception of the buccal fat pad, they form part of this deep fascia and do not constitute a continuation of layer 3.
The thickness of the deep fascia varies by region
Once it is established that the deep fascia constitutes the floor of the dissection, it matters that it does not offer the same reference throughout the surgical field. In the posterior regions — over the sternocleidomastoid, over the parotid capsule and in the upper frontal portion — it is thin, and the plane superficial to it is easy to find and to maintain. In the intermediate regions — deep temporal fascia and masseteric fascia — it reaches its greatest thickness and constitutes an identifiable lamina that serves as a reliable depth reference. In the anterior regions, where the SMAS no longer exists as such, the superficial fascia contacts the deep fascia directly and the two are distinguished only by the orientation of their fibres. It is, consequently, the zone where the correct plane is most easily lost.
The mimetic muscles within the scheme
The muscles of facial expression have one peculiarity that distinguishes them from the rest of the striated musculature: they insert into the dermis rather than between two bony structures. Hence their contraction displaces the skin, and their tone, atrophy or denervation translate immediately to the surface. For the surgeon, the relevant consequence is that their innervation reaches each muscle from its deep surface, so that a dissection remaining superficial to layer 3 does not compromise mimetic function. A flap raised above the SMAS preserves the muscles with their innervation intact; one raised beneath mobilises them en bloc, which is desirable when repositioning is sought and demands greater care with the dissection plane. The detailed study of each muscle, its layer and its nerve branch is covered in the section on the anatomy of facial animation.
What follows from this anatomy
The technical decisions of facelift surgery — the plane of dissection, the vector of traction, the ligaments to be released and the point at which to stop — are not independent options but consequences of the arrangement described. Recognising the plane by the appearance of the tissue rather than by estimated depth is what allows one to anticipate why a manoeuvre that is safe in the cheek ceases to be so a centimetre further forward. The following notes develop the elements this one introduces: the fat compartments and retaining ligaments, which explain the formation of the sulci, and the course of the facial and great auricular nerves, which delimit the zones of risk.
References
- 1.Mitz V, Peyronie M. The superficial musculo-aponeurotic system (SMAS) in the parotid and cheek area. Plast Reconstr Surg. 1976;58(1):80-88.
- 2.Mendelson BC, Wong CH. Surgical anatomy of the middle premasseter space and its application in sub-SMAS face lift surgery. Plast Reconstr Surg. 2013;132(1):57-64.
- 3.Rohrich RJ, Pessa JE. The fat compartments of the face: anatomy and clinical implications for cosmetic surgery. Plast Reconstr Surg. 2007;119(7):2219-2227.
- 4.Talei B. The deep plane facelift: anatomy and technique. Facial Plast Surg Clin North Am. 2024.
- 5.Sinclair NR, Coombs DM, Kwiecien G, Zins JE. How to prevent and treat complications in facial aesthetic surgery. Aesthet Surg J Open Forum. 2021;3(1):ojab007.
Related specialty: Facial Lifting & Rejuvenation