Hyaluronic Acid

What it is

Hyaluronic acid is a very long chain of repeating sugar units found throughout human connective tissue, where it acts as the skin's main water-holding molecule. Cosmetic hyaluronic acid is produced by fermenting bacteria, so it is vegan and not sourced from rooster combs as older grades were. On an ingredient list the free acid is less common than its salt, sodium hyaluronate, and the two behave essentially the same on skin. Its whole job in a mask is to attract and hold water in the top layers of the skin.

What it does well

• Reliably raises water content in the outer skin layers

  Multiple instrument-measured trials show increased stratum corneum hydration within hours and maintained over weeks. This is the claim the evidence best supports.

  Strong evidence

• Reduces measured wrinkle depth over weeks of use

  A 60-day study of five molecular weights found significant reductions in surface roughness for the 50 and 130 kDa grades versus placebo. The study was small and industry-linked, and the mechanism is surface plumping rather than collagen change.

  Moderate evidence

• Suits essentially all skin types, including acne-prone and sensitive

  It is oil-free, non-occlusive and has a very low reported rate of irritation or contact allergy, which is why it appears in products aimed at both oily and reactive skin.

  Strong evidence

Worth knowing

• "Low molecular weight penetrates deeper" is only partly true

  Ex vivo Raman imaging does show 20-300 kDa hyaluronic acid crossing the stratum corneum while 1000-1400 kDa grades do not, so the direction of the claim is real. But "deeper" means a few micrometres into the upper epidermis; no topical study has demonstrated cosmetic hyaluronic acid reaching the dermis or replacing dermal hyaluronic acid, and a tape-stripping study could only detect it in the stratum corneum.

  Matters most toAnyone paying a premium for a "multi-weight" or "nano" hyaluronic acid mask on the promise of deep dermal action.

• Claimed to dehydrate skin in low humidity

  The theory is that a humectant in dry air draws water from deeper skin to the surface where it evaporates. No published clinical study has shown this happening with topical hyaluronic acid at cosmetic concentrations, and the measured behaviour is that it stays in and hydrates the stratum corneum. The practical point that survives is that humectants perform better when followed by a moisturiser that slows evaporation.

  Matters most toPeople using hyaluronic acid alone in arid climates or heavily heated rooms and finding it underwhelming.

• Benefits stop when you stop

  The effect is physical water-binding, not a lasting change to the skin. Hydration and the softened look of fine lines fade within days of discontinuing.

  Matters most toAnyone expecting a durable anti-ageing result from hyaluronic acid alone.

Where the EU stands

Sources (3)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   Human skin penetration of hyaluronic acid of different molecular weights as probed by Raman spectroscopy

   Skin Research and Technology · 2016 · doi:10.1111/srt.12228

   Low molecular weight hyaluronic acid (20-300 kDa) passed through the stratum corneum in ex vivo human skin, while high molecular weight grades (1000-1400 kDa) did not penetrate at all.

2. [2]
   Efficacy of cream-based novel formulations of hyaluronic acid of different molecular weights in anti-wrinkle treatment

   Journal of Drugs in Dermatology · 2011

   All 0.1% hyaluronic acid formulations improved hydration and elasticity, but only the 50 and 130 kDa grades significantly reduced measured wrinkle depth versus placebo after 60 days.

3. [3]
   Hyaluronic acid skin penetration evaluated by tape stripping using ELISA kit assay

   Journal of Pharmaceutical and Biomedical Analysis · 2023 · doi:10.1016/j.jpba.2022.115205

   Repeated application produced measurable accumulation of hyaluronic acid in the stratum corneum; the method could not detect it in the epidermis or dermis, supporting a surface-layer mechanism.