The Science of Hyaluronic Acid in Aesthetic Medicine

Hyaluronic acid (HA) is arguably the single most important molecule in aesthetic medicine. From dermal fillers to skin boosters, bio-remodelling treatments to topical skincare, HA is ubiquitous, and for good reason. This naturally occurring substance plays a critical role in skin hydration, structure, and repair, making it an invaluable tool for practitioners and a trusted ingredient for patients.

The clinical team has worked extensively with hyaluronic acid-based products across the full spectrum of aesthetic applications. This article provides a thorough, science-backed exploration of what HA is, how it works, and why it remains the cornerstone of modern aesthetic practice.

What is hyaluronic acid?

Hyaluronic acid is a glycosaminoglycan, a type of sugar molecule, that occurs naturally throughout the human body. It is found in particularly high concentrations in the skin, connective tissue, and eyes. The average 70kg adult contains approximately 15 grams of HA, with roughly half of this located in the skin.

The molecule’s most remarkable property is its extraordinary capacity to bind water. A single gram of hyaluronic acid can hold up to six litres of water, making it one of the most hygroscopic (water-attracting) substances found in nature. This property is fundamental to its role in maintaining skin hydration, volume, and resilience.

Hyaluronic acid in the skin: Natural functions

In healthy skin, HA performs several essential functions:

• Hydration: By binding water in the extracellular matrix, HA maintains skin moisture levels and creates a plump, supple appearance.
• Structural support: HA provides the gel-like matrix in which collagen and elastin fibres are embedded, which adds to skin firmness.
• Wound healing: HA modulates inflammation and promotes tissue repair, playing a critical role in the skin’s healing processes.
• Free radical defence: HA has antioxidant properties that help protect skin cells from oxidative damage.
• Cell signalling: HA fragments of different molecular weights trigger various cellular responses, influencing inflammation, cell proliferation, and angiogenesis.

Age-related HA decline

As we age, the body’s production of hyaluronic acid decreases significantly. By the age of 50, the average person retains only about half the HA they had at 25. This decline contributes directly to the visible signs of ageing:

• Loss of skin moisture and the development of a dull, dehydrated appearance
• Reduced skin elasticity and firmness
• Formation of fine lines and wrinkles
• Loss of facial volume, particularly in the cheeks, temples, and perioral area

Hyaluronic acid in injectable treatments

Dermal Fillers

HA-based dermal fillers are the most widely used injectable fillers worldwide. They work by physically adding volume beneath the skin’s surface, restoring lost volume and smoothing lines. Modern HA fillers are cross-linked using agents such as BDDE (1,4-butanediol diglycidyl ether) to increase their longevity and resistance to enzymatic degradation.

Different HA fillers are formulated with varying degrees of cross-linking, concentration, and particle size to suit specific treatment areas:

• High cross-linking, larger particles: Cheeks, jawline, chin, for volumising and contouring
• Medium cross-linking: Nasolabial folds, marionette lines, for moderate volume and smoothing
• Low cross-linking, fine particles: Lips, under-eye area, fine lines, for subtle enhancement and hydration

Skin Boosters

Skin boosters (such as Restylane Skinboosters and Juvederm Volite) are lightly cross-linked HA products designed not to add volume but to improve skin quality from within. Injected superficially across the face, neck, hands, or décolletage, they provide deep hydration and gradual improvement in skin texture and elasticity.

Bio-remodelling (Profhilo)

As we have discussed in our comprehensive Profhilo guide, bio-remodelling products use ultrapure, non-cross-linked HA at high concentrations. Rather than adding volume or simply hydrating, these products stimulate the body’s own production of collagen and elastin through a biological remodelling process.

Hyaluronic acid in topical skincare

HA is a staple ingredient in modern skincare formulations. However, it is important to understand the differences between molecular weights and their effects:

High molecular weight HA (1,000-1,500 kDa)

These large molecules sit on the skin’s surface, forming a moisture-retaining film. They provide immediate hydration and a smoothing effect but do not penetrate the epidermis.

Medium molecular weight HA (100-1,000 kDa)

These molecules can partially penetrate the outer layers of the skin. This provides both surface and slightly deeper hydration.

Low molecular weight HA (less than 100 kDa)

These smaller fragments can penetrate more deeply into the epidermis, stimulating cellular processes and providing longer-lasting hydration. Some research suggests they may also stimulate the skin’s own HA production.

“The most effective topical HA formulations contain a combination of molecular weights. This provides both immediate surface hydration and deeper, more sustained moisturisation. We advise patients to look for multi-weight HA serums as part of their daily skincare regimen.”

The reversibility advantage

One of the most significant safety advantages of HA-based fillers is their reversibility. The enzyme hyaluronidase can be used to dissolve HA fillers if complications arise or if the patient is unhappy with the result. This enzyme breaks down the cross-linked HA, returning the tissue to its pre-treatment state within 24-48 hours.

This reversibility is unique to HA fillers and is not available with other filler types such as calcium hydroxylapatite (Radiesse) or poly-L-lactic acid (Sculptra).

Safety of HA-based treatments

HA-based injectables have an excellent safety profile due to the biocompatible nature of the molecule. Since HA is naturally present in the body, allergic reactions are extremely rare. The most common side effects are:

• Temporary swelling and redness at injection sites
• Bruising (common but transient)
• Tenderness
• Minor asymmetry (correctable at follow-up)

More serious but rare complications include vascular occlusion (if filler is inadvertently injected into or compresses a blood vessel), infection, and granuloma formation. These risks are significantly minimised by choosing an experienced, anatomically knowledgeable practitioner.

Emerging research and future directions

The field of HA-based aesthetic treatments keeps changing rapidly. Current areas of research and development include:

• Next-generation cross-linking: New cross-linking technologies aim to improve filler longevity whilst maintaining natural tissue integration.
• HA-based drug delivery: Research into using HA as a carrier for other active molecules (growth factors, peptides, vitamins) directly into the skin.
• Oral HA supplements: Emerging evidence suggests that oral HA supplementation (120-240mg daily) may improve skin moisture and reduce wrinkle depth, though more robust clinical trials are needed.
• Combination products: Development of HA products combined with other bio-stimulatory agents for enhanced collagen and elastin production.

Frequently asked questions

Conclusion

Hyaluronic acid’s unique properties make it an indispensable molecule in aesthetic medicine. Whether delivered via injection, applied topically, or ingested as a supplement, HA continues to demonstrate its value in maintaining and restoring skin health. As research advances, we can expect even more sophisticated and effective HA-based treatments to emerge.

This article reflects current scientific understanding and clinical practice as of 2025. For treatment recommendations tailored to your skin, please contact a clinic to arrange a consultation.