Hyaluronic acid (HA) is the most popular hydrating ingredient in skincare — and the most misunderstood. Does it dry out your skin? Can molecules be too large? Is more always better? Let's separate the science from the marketing.
Hyaluronic acid is a glycosaminoglycan — a long-chain sugar molecule that occurs naturally in your skin. It's the body's primary moisture-binding molecule, capable of holding up to 1,000 times its weight in water.
In skincare, HA functions as a humectant — it draws water from the environment and from deeper skin layers into the stratum corneum (the skin's outermost layer).
Not all hyaluronic acid is created equal. The molecular weight (measured in Daltons / kDa) determines how deeply it penetrates:
| Molecular Weight | Penetration | Effect | |-----------------|-------------|--------| | High (>1,000 kDa) | Surface only | Immediate surface hydration, film-forming | | Medium (100–1,000 kDa) | Epidermis | Sustained hydration, barrier support | | Low (<100 kDa / "micro-HA") | Deeper epidermis | Longer-lasting hydration, anti-ageing signals | | Very Low (<50 kDa) | Dermis (potentially) | Pro-inflammatory at high amounts |
The best serums use a mix of molecular weights — high for surface, low for deeper penetration. Products with only high-molecular-weight HA sit on the surface and wash off.
HA draws water into the skin, which plumps fine lines instantly. This is why HA serums give a "glass skin" effect.
A well-hydrated barrier is more flexible and resilient. HA supports the lipid matrix by maintaining optimal water content.
HA plays a role in tissue repair. Studies show it accelerates healing of wounds and reduces scarring.
HA serums often contain other antioxidants (Vitamin C, ferulic acid) — the water-based formula acts as a delivery vehicle.
The claim: If applied in dry conditions (low humidity), HA draws water from deeper skin layers outward, causing dehydration.
The reality: This can happen — but only if you apply HA to bare skin without a moisturiser on top in very dry environments (<20% humidity). In the UK's naturally humid climate, this is rarely an issue.
How to use HA correctly:
A multi-weight HA with Vitamin B5 (panthenol). Three HA molecular weights plus cross-polymer for surface hydration. Outstanding value.
Buy: Amazon UK
Contains sodium hyaluronate at multiple weights plus panthenol and glycerin. Rich, cushioning feel.
Buy: Amazon UK
Combines two molecular weights of HA with Vitamin B5 and Madecassoside. Excellent for sensitive, dehydrated skin.
Buy: Amazon UK | Feelunique | Lookfantastic
Not pure HA, but snail mucin contains naturally occurring glycoproteins and hyaluronic acid. A cult favourite for glass skin.
Buy: Amazon UK | Lookfantastic
| Feature | Hyaluronic Acid | Glycerin | |---------|----------------|----------| | Humectant strength | Holds 1,000× weight in water | Holds ~200× weight | | Feel | Lightweight, slightly tacky | Slightly heavier, smooth | | Penetration | Multi-weight (surface to deep) | Surface to mid-epidermis | | Cost | Moderate | Very cheap | | Best for | Layering, serums | All-purpose hydration |
Verdict: Both are excellent humectants. The best products use both.
In very dry environments (<20% humidity), HA can theoretically pull water from deeper layers. This is easily prevented by applying HA to damp skin and following with a moisturiser. In the UK's humid climate, this is rarely a concern.
1–2% is optimal for a serum. Higher concentrations can feel sticky and pill under other products. The molecular weight mix matters more than raw percentage.
Yes. Apply HA first, let absorb, then apply retinol. HA provides a hydrating buffer that reduces retinol irritation.
Sodium hyaluronate is the sodium salt of hyaluronic acid. It's smaller, more stable, and penetrates skin better than pure HA. Most good serums use sodium hyaluronate.
Yes — HA is safe for twice-daily use by all skin types, including sensitive and acne-prone skin.
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