Hyaluronic acid for skin
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Hyaluronic acid is a glycosaminoglycan found naturally in skin, where it binds water. On skin, molecular weight decides what it does: high-molecular-weight HA (1,000 to 1,400 kDa) stays on the surface as a water-holding film that reduces water loss and makes skin look plumper, while low-molecular-weight HA (20 to 300 kDa) passes through the stratum corneum. Both are useful for different jobs.
Why does hyaluronic acid molecular weight matter?
Hyaluronic acid is a glycosaminoglycan found naturally in skin and connective tissue, where it binds water and contributes to volume and mechanical properties. In cosmetics it appears as the acid and as various salts and derivatives, in molecular weights spanning three orders of magnitude - and molecular weight is the single most important variable.
Does hyaluronic acid penetrate the skin?
This is unusually well characterized. Raman micro-imaging of human skin found that low-molecular-weight HA in the 20 to 300 kDa range passes through the stratum corneum, while high-molecular-weight HA at 1000 to 1400 kDa is effectively impermeable. Fractions at 5 and 8 kDa penetrate readily. Below about 8 kDa, penetration appears to be assisted by HA's own hydration effect, its interaction with keratin and lipids, and CD44 receptor-mediated uptake.
The practical translation: high-molecular-weight HA works at the surface, holding water in a film that reduces measured water loss and makes skin look and feel plumper. Low-molecular-weight HA can actually get in. Both are useful; they are not doing the same job, and a product that only contains the high-molecular-weight form cannot claim to be acting below the surface.
High-molecular-weight HA can be driven into the stratum corneum with an enhancer such as magnesium chloride, or vectorised with clay, but those are specific formulation strategies rather than a property of HA itself.
Why combine high and low molecular weight hyaluronic acid?
Vegalab's Hyaluronic Skin Repair uses a stated dual molecular weight system, high (around 1000 kDa) and low (around 50 kDa), at 75 mg per application. : the high-weight fraction is a surface humectant and film former, the low-weight fraction sits within the range shown to cross the stratum corneum. Describing both as "penetrating" would be wrong; describing the pairing as covering two different mechanisms is accurate.
Does a long list of hyaluronic acid forms mean more hyaluronic acid?
The Youlief range lists eight distinct HA forms: sodium hyaluronate, hydrolyzed hyaluronic acid, hyaluronic acid, hydrolyzed sodium hyaluronate, potassium hyaluronate, hydroxypropyltrimonium hyaluronate, sodium hyaluronate crosspolymer and sodium acetylated hyaluronate.
Only two are present at levels that can plausibly do anything: sodium hyaluronate at 0.02% and hydrolyzed hyaluronic acid at 0.006%. The remaining six sit at 1 part per million or below, and the crosspolymer at 0.02 ppm. Those are label-claim quantities.
This is worth stating because the industry practice of listing many HA variants implies a sophistication that the concentrations do not support. A long HA list is not the same as a lot of HA. The two functional forms here are well chosen - one surface humectant, one in the penetrating weight range - and that is the story.
What does hyaluronic acid not do?
It does not stimulate your own HA synthesis in any established way at topical levels. It does not fill lines the way injected HA does; injectable and topical HA are the same molecule doing entirely different jobs at entirely different depths. And in very dry air a heavy high-weight HA layer with nothing occlusive over it can draw water from skin rather than into it, which is why HA is applied to damp skin and sealed.
Key takeaways
- Molecular weight is the single most important variable for topical hyaluronic acid.
- Low-molecular-weight HA (20 to 300 kDa) crosses the stratum corneum; 1,000 to 1,400 kDa HA is effectively impermeable.
- High-molecular-weight HA works at the surface, holding water in a film that reduces measured water loss.
- A long HA ingredient list is not the same as a lot of HA.
- Apply HA to damp skin and seal it, because in very dry air a heavy layer can draw water out of skin.
References
The studies below describe the ingredient itself. Finished-product results appear in each product's evidence dossier.
- Essendoubi et al., Human skin penetration of hyaluronic acid of different molecular weights probed by Raman spectroscopy, Skin Research and Technology 2016
- Biocompatible topical delivery of high-molecular-weight hyaluronan into human stratum corneum using magnesium chloride
- Interactions of Hyaluronic Acid with the Skin and Implications for Dermal Delivery of Biomacromolecules, Molecular Pharmaceutics
- High molecular weight hyaluronic acid vectorised with clay provides long-term hydration, Skin Research and Technology 2024
- Bos & Meinardi, The 500 Dalton rule for skin penetration, Experimental Dermatology 2000
Frequently asked questions
Does molecular weight matter?
Yes, it is the single most important variable. Raman imaging of human skin found low-molecular-weight HA in the 20 to 300 kDa range passes through the stratum corneum, while high-molecular-weight HA at 1,000 to 1,400 kDa is effectively impermeable. A product with only the high-weight form cannot claim to act below the surface.
Can hyaluronic acid dry out skin?
It can in very dry air. A heavy high-weight HA layer with nothing occlusive over it can draw water from skin rather than into it. That is why HA is applied to damp skin and sealed.
Does topical hyaluronic acid fill lines like injected HA?
No. Injectable and topical HA are the same molecule doing entirely different jobs at entirely different depths. Topical HA also does not stimulate your own HA synthesis in any established way.
Can high-molecular-weight HA be made to penetrate?
It can be driven into the stratum corneum with an enhancer such as magnesium chloride, or vectorized with clay. Those are specific formulation strategies rather than a property of HA itself.
Related reading
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Products containing hyaluronic acid
Listed because this ingredient appears in each product's declared composition. This is a commercial link from a reference page; it is not a recommendation, and approved uses and availability vary by market.