The Science of Dermal Fillers: A Doctor Explains Hyaluronic Acid, Facial Anatomy and Natural Volume

What hyaluronic acid fillers are, how they interact with facial anatomy, why the face ages in three dimensions, and why placement matters more than product.

By Dr Amber Halliday, MRCGP MBBS BSc (Hons) — GP & Aesthetics Doctor  |  Blue Bird Aesthetics, Worthing  |  Updated 2026

The Question Patients Don’t Always Ask

When a patient asks me about dermal fillers, most of the conversation centres on results — what areas respond, how long it lasts, what the risk of looking different is. All important questions. But the question that tends not to get asked is the most useful one: what exactly is a filler, and how does it interact with my face?

I find that patients who understand what a filler is — and how it interacts with their anatomy — make better decisions, have more realistic expectations, and are more satisfied with their outcomes. So here is the molecular biology, the anatomy, and the clinical context.

What Hyaluronic Acid Is and Why It Matters

Hyaluronic acid (HA) is a naturally occurring molecule found throughout the human body — in skin, joints, and connective tissue. In the skin, its primary role is to bind water: a single HA molecule can hold up to 1,000 times its weight in water, which is what gives young skin its plumpness and resilience. As we age, the skin’s HA content falls, contributing to volume loss and reduced elasticity.

HA is not static. It is constantly being produced and broken down by the body — the half-life of natural HA in the skin is about 24 hours. Injectable HA is manufactured synthetically and cross-linked — chemically modified to last far longer, typically months to over a year depending on the product and area.

How Fillers Are Made Different From Each Other

Not all HA fillers are the same, and this matters more than most patients realise. The key variable is cross-linking — the process that determines how stiff, how soft, and how long-lasting a filler is.

• Higher cross-linking produces a firmer, more viscous filler — better suited to structural support deep in the face, such as the cheeks or chin.
• Lower cross-linking produces a softer, more fluid filler — better suited to delicate areas such as the lips or fine surface lines.

Clinicians also refer to a property called G’ (G prime) — the elastic quality of the gel, essentially how well it resists deformation under pressure. A high-G’ filler holds its shape under movement; a low-G’ filler integrates softly into tissue. Choosing the right filler for the right area at the right depth is a clinical decision based on assessment, not a product preference.

The Face Is Not a Flat Canvas — Why Layers Matter

One of the things that makes facial aesthetics medical is that the face has multiple distinct tissue layers, each with different anatomy, different blood supply, and different risk profiles. Injectable treatments are placed at specific depths for clinical reasons, not arbitrary ones.

• The dermis (superficial): fine surface lines, very fine lip lines — softer, low-G’ product.
• Subcutaneous fat layer (mid-depth): most lip enhancement and general volume work sits here.
• Sub-muscular and periosteal (deep): structural support for cheeks, chin and jaw often goes here, providing a foundation for overlying tissue.

A practitioner who understands these layers — and who has trained extensively in facial anatomy — can place product precisely and safely. Incorrect depth placement is one of the primary causes of unnatural results and complications.

How the Face Ages — the Three-Dimensional Picture

Volume loss is not simply “skin getting thinner.” It is a three-dimensional process involving bone, fat and skin simultaneously. Treating it well requires understanding all three.

Bone resorption

Facial bones thin and remodel with age. The orbital rim (around the eye) widens. The mid-face bone loses forward projection. The mandible (jaw) resorbs at its edges. This skeletal change underlies much of what we see as “ageing” — the foundation shifts, and everything above it follows.

Fat compartment deflation

The face has multiple discrete fat compartments, each of which deflates and descends independently with age. The malar fat pad descends; the nasolabial fold deepens not because the fold “grows” but because the cheek above it falls. Understanding this is why I often address the cheek to improve the lower face, rather than simply treating the fold directly.

The cascade effect

Here is something that surprises many patients: treating the cheeks often changes the appearance of the nasolabial folds, the midface, and the overall facial proportion — without touching those areas at all. Volume at the right structural point creates a cascade of lift and support through the face.

Reversibility and Hyaluronidase

One of the most important safety features of HA-based dermal fillers is that they are reversible. Hyaluronidase is an enzyme that breaks down HA — it is used both as an emergency treatment if a vascular complication arises, and electively to dissolve filler that a patient is unhappy with.

It is not an instant erase. Hyaluronidase works over 24–72 hours and may require more than one session to dissolve filler completely, particularly if multiple treatments have accumulated. But the reversibility of HA fillers is a meaningful safety advantage over permanent or semi-permanent alternatives. Full information is on my filler dissolving page.

Why Placement Matters More Than Product

Patients sometimes ask which brand of filler is used, as though the brand were the determining factor in the outcome. It is not. The same filler in two different practitioners’ hands, placed at different depths with different volumes and at different anatomical points, will produce entirely different results — one natural, one not.

Assessment, anatomical understanding, and clinical experience are the primary determinants of a good outcome. Product selection follows from those, not the other way around.

Further Reading & Related Treatments

• Are Dermal Fillers Right for You? A Doctor’s Decision Guide
• Volume or Skin Quality? Why ‘Looking Tired’ Isn’t Always Filler
• Filler Dissolving (Hyaluronidase) in Worthing
• How to Choose a Safe Aesthetics Clinic in Worthing
• The Ultimate Guide to Aesthetic Treatments in Worthing

Frequently Asked Questions