Unit 1 · The biology of facial ageing
Four tissue systems age at once, and they do not age at the same rate
This unit establishes what ageing actually does to skin, fat, muscle and bone. By the end you should be able to name which tissue is driving a given presentation, explain why skin quality governs whether restored volume lifts or displaces, and read the face as layers rather than as a surface.
Framing
The gap this module closes
Injectable aesthetics is volume restoration — but to restore volume intelligently, you first need a granular understanding of what ageing actually does to the face.
This module is not about products. It is about anatomy: how collagen, fat and bone change across decades, how these changes manifest differently across sexes and ethnic backgrounds, and what the structural principles of volume restoration are before any product decision is made.
The clinical practitioner who understands the ageing face at the anatomical and histological level makes fundamentally different treatment decisions to one who simply learns product protocols. This module establishes that foundation.
Facial ageing is not a single process. It is the concurrent and interacting decline of four anatomical systems: skin, subcutaneous fat, muscle and bone. Understanding each system, and how they relate to one another, is the prerequisite to any intelligent volume restoration strategy.
Learn · Skin
Collagen, elastin and the hydration deficit
Collagen
The dermis is approximately 70–80% collagen by dry weight, predominantly Type I (structural, tensile strength) and Type III (finer fibres, wound healing). From approximately age 25, collagen synthesis declines at roughly 1% per year. By age 45, a patient may have lost 20% of their peak collagen mass. Post-menopausal women experience an accelerated decline — approximately 30% of dermal collagen is lost in the first five years after menopause, primarily driven by the withdrawal of oestrogen’s direct stimulation of fibroblast activity.
Simultaneously, existing collagen undergoes glycation and cross-linking — abnormal molecular bonding that makes fibres stiffer and less organised. This is a change in the quality of the collagen that remains, not only in its quantity.
Two patients present at the same chronological age. One has spent three decades outdoors and looks a decade older than the other. Collagen decline is time-dependent, so what makes UV exposure outrun the clock?
Hold your answer before you open this. The value is in having committed to a mechanism first.
UV exposure (Type B and A) dramatically accelerates both collagen degradation and cross-linking via matrix metalloproteinase (MMP) upregulation. This is why photoageing consistently precedes chronological ageing in visible presentation.
Clinically, this is the reason a stated age tells you very little on its own. The assessment is of the tissue in front of you, not of the number on the file.
Elastin
Elastin fibres provide the skin’s recoil — the ability to return to its resting state after expression or movement. Unlike collagen, elastin fibres are laid down almost entirely in the first two decades of life. The adult dermis does not produce meaningful new elastin. With age and UV exposure, existing elastin undergoes solar elastosis — fragmentation and calcification of fibres, reducing tissue recoil. The visible result is skin that folds rather than springs back, and that loses its ability to adapt to underlying volume changes.
Hyaluronic acid and glycosaminoglycans
Hyaluronic acid is the extracellular matrix’s primary hydrophilic molecule, binding up to 1000 times its weight in water and providing tissue turgor, plumpness and volume. GAG production declines with age, reducing tissue hydration and contributing to the flattened, dull appearance associated with intrinsic ageing — separate from wrinkle formation.
This hydration component of volume loss is distinct from fat atrophy and is often underappreciated clinically. A face can be deflated at the level of the dermis while its fat compartments are still reasonably intact, and the two deficits are not addressed in the same plane.
A patient in her late fifties with marked solar elastosis asks for cheek restoration. The volume deficit is real and the compartments are clearly deflated. Before you plan anything, what does her skin quality tell you about the likely result?
Hold your answer before you open this. The value is in having committed to a mechanism first.
Skin quality is a critical variable in assessing volume restoration candidacy. A patient with good skin quality — adequate collagen density, reasonable elasticity — will respond predictably to volume restoration. A patient with markedly poor skin quality has a dermis that cannot adapt to the volume placed beneath it.
In that context, restoration often displaces rather than lifts. The volume deficit being genuine is not by itself an indication to treat it.
From approximately age 25, dermal collagen synthesis declines at roughly what rate per year?
Select an option to commit. The reasoning appears afterwards.
Collagen synthesis declines at approximately 1% per year from the mid-20s. Compounded, that places a patient at around a 20% deficit from peak by age 45 — before any accelerated post-menopausal decline is added.
The number matters because it sets the baseline expectation. A steady 1% annual decline is the floor; UV exposure, glycation and oestrogen withdrawal are what move an individual patient above it. When a presentation is markedly ahead of chronological age, one of those accelerants is doing the work.
A patient asks why her skin now creases where it used to spring back, given that she has had collagen-stimulating treatment. The most accurate structural explanation is:
Select an option to commit. The reasoning appears afterwards.
Elastin fibres provide recoil — the return to a resting state after movement. They are laid down almost entirely in the first two decades, and the adult dermis does not produce meaningful new elastin. Solar elastosis then fragments and calcifies the fibres that exist.
The consequence for practice is that recoil is not a renewable asset in the way collagen density partly is. Skin that folds rather than springs back has lost its ability to adapt to underlying volume changes, which is precisely the property volume restoration relies on.
Learn · Fat
Compartments that atrophy and descend at the same time
The subcutaneous fat of the face is not a single layer — it is a collection of discrete, anatomically defined compartments, each with its own blood supply, innervation and ageing trajectory. These compartments are bounded by retaining ligaments and fibrous septa. Their behaviour is the single most important driver of the visible ageing face.
Fat pads do not simply disappear. They undergo two concurrent processes: atrophy (reduction in volume) and gravitational descent (ptosis). The combination creates the classic signs of facial ageing: hollowing superiorly and accumulation of tissue inferiorly.
Because the two processes run together, the same face can be simultaneously empty above and heavy below. Reading a presentation as purely deflation, or purely descent, produces a treatment plan that addresses half of it. Unit 2 takes the compartments individually.
Learn · Muscle
Hypertrophy, atrophy and the weakening sling
Repeated muscular contraction causes dynamic rhytids that, over time, become static through dermal damage and the loss of recoil described above. With age, some muscles hypertrophy from overuse — the masseter in bruxists, the platysma as it loses opposing subcutaneous support — while others become less active.
The muscular sling that supports facial soft tissue weakens, contributing to gravitational descent of the overlying fat compartments. Muscle is therefore both a generator of lines and a component of the support structure that fails.
Learn · Bone
The foundation itself moves
The facial skeleton provides the foundation on which all soft tissue rests. With age — and particularly dramatically in post-menopausal women — the facial bones resorb. The orbital rim expands, giving a greater volume of space within the orbit. The maxilla retracts, reducing mid-face projection and malar eminence support. The mandible loses height and width, shortening the lower face and reducing chin projection.
Bone loss directly affects soft tissue position: tissue that was once supported by a fuller maxilla hangs unsupported, exaggerating nasolabial folds and producing a relative descent of the mid-face.
Some patients present with primarily skeletal volume loss, requiring deep periosteal restoration. Others present with primarily fat pad atrophy, requiring a different plane of approach. Distinguishing the two at assessment is what determines the plane you work in, and it is a distinction made before any product is considered.
A woman in her mid-fifties presents with a deepening nasolabial fold and a flattened mid-face. Her cheek fat compartments are deflated but her main structural change is maxillary retraction. The mechanism most directly responsible for the fold appearance is:
Select an option to commit. The reasoning appears afterwards.
The maxilla retracts with age, reducing mid-face projection and malar eminence support. Tissue that was once supported by a fuller maxilla hangs unsupported. The fold deepens because its foundation has moved backwards, not only because the tissue above it has deflated.
This is the distinction that decides your plane. A deficit that is skeletal in origin is addressed with deep periosteal restoration; a deficit that is compartmental is addressed in the fat planes. Treating a skeletal deficit superficially adds volume to tissue that still has nothing underneath it.
Learn · Tissue layers
Reading the face as layers, superficial to deep
Every decision in this module resolves to a question of layer. The table below is the reference frame for the rest of the series.
| Layer | What sits here | Restoration implication |
|---|---|---|
| Epidermis and dermis | Collagen, elastin and HA. Primary site of photoageing, hydration decline and surface texture change. Dynamic rhytids originate here. | Intradermal and subdermal restoration planes address this layer. |
| Superficial fat compartments | Discrete fat pads above the SMAS: nasolabial, medial, middle and lateral cheek, orbital, jowl and temporal. First to show visible atrophy and descent. | Subdermal and subcutaneous restoration addresses this layer. |
| SMAS and muscle | The superficial muscular aponeurotic system, which transmits muscular movement to facial soft tissue. Weakening of the SMAS contributes to gravitational descent. | The surgical plane for rhytidectomy. |
| Deep fat compartments | Deep medial cheek fat, SOOF, deep temporal and buccal fat. These support the overlying superficial compartments; atrophy here causes subsidence of everything above. | Supraperiosteal and periosteal restoration addresses this layer. |
| Periosteum and bone | The facial skeleton — the foundation for all overlying tissue. Bone resorption reduces projection and support. | Periosteal plane injection directly addresses skeletal support deficit. |
Learn · Regulatory position
The regulatory frame around everything that follows
This module discusses classes of intervention rather than products. That is a regulatory position as much as an editorial one, and it holds for every unit that follows.
All content in this module uses generic terminology consistent with TGA scheduling requirements. Botulinum toxin type A products are Schedule 4 Prescription Only medicines in Australia and must be prescribed by an authorised prescriber. Injectable volume restoration is discussed by product class only — hyaluronic acid dermal fillers and biostimulators — and no product-specific claim is made or implied. Practitioners must refer to current product-specific prescribing and device information before use.
Unit 1 summary
Clinical takeaways
- Ageing is four systems, not one. Skin, subcutaneous fat, muscle and bone decline concurrently and interact. Naming which system is driving a presentation is the first step of assessment.
- Collagen declines about 1% per year from age 25, and faster after menopause. Approximately 30% of dermal collagen is lost in the first five years post-menopause. UV exposure accelerates both degradation and cross-linking through MMP upregulation.
- Elastin is not replaced in the adult dermis. Recoil is laid down in the first two decades and degraded by solar elastosis. Skin that folds rather than springs back cannot adapt to volume placed beneath it, and restoration in that context displaces rather than lifts.
- Bone resorption moves the foundation. Orbital expansion, maxillary retraction and mandibular loss leave soft tissue unsupported. A skeletal deficit and a compartmental deficit look similar on the surface and are treated in different planes.