Hyaluronic Acid

How it works

Hyaluronic acid is a glycosaminoglycan, a long-chain polysaccharide built from repeating disaccharide units of N-acetylglucosamine and glucuronic acid. In native skin, it resides in the extracellular matrix of the dermis where it maintains tissue hydration and viscoelasticity. Topical HA cannot penetrate intact skin to reach the dermis because of its molecular size (typically 1 million Daltons for native HA, 200 to 500 kDa for medium-weight cosmetic HA, and 5 to 50 kDa for low-molecular-weight fragments). Instead, topical HA binds water at the skin surface and in the upper stratum corneum, producing a hydration effect via humectant action rather than dermal augmentation. The common industry practice of combining multiple molecular weights addresses different skin layers: high MW films the surface, low MW penetrates deeper in the stratum corneum.

Clinical evidence

Clinical efficacy of topical HA for skin hydration has been documented in dozens of randomised split-face and placebo-controlled trials. A 2011 review in the Journal of Drugs in Dermatology pooled evidence across 11 studies showing 10 to 40% improvement in skin hydration measurements (corneometry) within 2 to 4 weeks of use at 0.1 to 2% concentrations. Wrinkle-depth reduction is smaller and slower: 10 to 20% improvement over 8 to 12 weeks, which is a cosmetic smoothing effect from hydration rather than dermal restructuring. No serious adverse events reported across any of the reviewed trials. CIR Expert Panel safety reassessment confirms non-irritant status across the concentration range used in cosmetics.

Dosing and protocol

Apply topical HA to damp skin twice daily. On dry skin in a dry environment, HA can paradoxically draw water from deeper skin layers, so always seal with a moisturiser within 60 seconds of application. Multi-MW formulations (The Ordinary Hyaluronic Acid 2% + B5, Vichy Mineral 89, Skinceuticals HA Intensifier) combine high and low molecular weights for broader hydration effect. Pure HA serums at 1 to 2% are optimal; above 3% the texture becomes tacky without proportional benefit.

Interactions with other actives

No known incompatibilities. HA layers under and over every other active in skincare. Use it as the first hydrating step after cleansing or toning, before heavier creams and occlusives. The only subtlety: applying HA on bone-dry skin in low humidity pulls moisture from inner layers, so pair with a damp-skin application technique or a finishing occlusive.

Common mistakes

The classic HA mistake is applying it to visibly dry skin in a low-humidity environment (heated homes in winter, air-conditioned offices) without sealing. The humectant pulls water from wherever it can find it, including the deeper epidermis, producing a net dehydration effect. The fix is trivial: apply to damp skin and seal with moisturiser. The other mistake is chasing expensive HA-only serums when a standard moisturiser already contains HA in combination with ceramides and glycerin for better overall barrier support.

FAQ

Is HA safe during pregnancy?

Yes. Zero systemic absorption due to molecular size, no teratogenicity signal, no regulatory restriction.

Does HA help acne?

Indirectly. HA is not an acne-treating active but it supports barrier recovery after harsh acne treatments (retinol, benzoyl peroxide, salicylic acid). Use it as the hydrating layer in a barrier-focused routine.

Sources

• Papakonstantinou E et al. HA skin function review. Dermatoendocrinol 2012
• Bukhari SNA et al. HA skincare review. Int J Biol Macromol 2018
• CIR safety assessment: Hyaluronic Acid
• EU CosIng entry: Sodium Hyaluronate
• DermNet NZ: Emollients and moisturisers