Buying Guide
Hyaluronic Acid: The UK Guide
What hyaluronic acid actually does, which molecular weights matter, and the UK products worth using. Everything practical, nothing vague.
Hyaluronic acid is one of the most popular skincare ingredients on the market. Every brand from The Ordinary to La Roche-Posay sells a hyaluronic acid serum. The marketing claims are everywhere. Hydration, plumping, anti-ageing, barrier support.
Some of those claims are accurate. Some are not. The quality of the product, the concentration, the molecular weight of the hyaluronic acid used, and how you apply it all determine whether a product actually delivers on its promises.
What does hyaluronic acid actually do?
Hyaluronic acid is a naturally occurring polysaccharide found in the skin, joints, and connective tissue. In skincare, it works as a humectant. It draws water from the environment and from the deeper layers of the skin and holds it in the outer layer, the stratum corneum.
Applied correctly, it:
- Improves skin hydration by drawing and retaining water in the outer skin layer
- Temporarily plumps the skin, reducing the appearance of fine lines for a few hours
- Supports the skin barrier by maintaining moisture levels in the outer layer
- Creates a dewy finish when used in the morning under moisturiser and SPF
The important caveat is the word "temporarily." Hyaluronic acid hydrates the surface of the skin. It does not penetrate deeply or change the underlying structure of the skin. Any plumping effect fades after a few hours. That does not make it useless, it just means it needs to be used consistently and alongside other ingredients for meaningful hydration.
Molecular weight matters more than most people realise
Not all hyaluronic acid is the same. It comes in different molecular sizes, and this is the most important factor in whether a product actually works.
- High molecular weight HA (above 1 million Da): Too large to penetrate the skin. It sits on the surface and draws water from the environment. Effective for surface hydration but can feel sticky and does not reach deeper layers.
- Low molecular weight HA (below 1 million Da): Can penetrate the outer skin layer and hydrate from within. More effective at plumping and long-term hydration. Less sticky on the surface.
- Hydrolysed HA: Broken down into smaller fragments that can penetrate further. A middle ground between high and low molecular weight.
The best hyaluronic acid products use multiple molecular weights. High molecular weight for surface hydration and film formation. Low molecular weight for deeper hydration. The Inkey List Hyaluronic Acid Serum, for example, uses three different molecular weights of HA.
Check the label. If a product lists only "hyaluronic acid" without specifying the type, it is probably using high molecular weight HA, which is cheaper and less effective.
The UK products worth considering
The Inkey List Hyaluronic Acid Serum
Around 9.99 on Amazon UK
Uses three different molecular weights of hyaluronic acid: high, medium, and low. This means it hydrates both the surface and the deeper layers of the skin simultaneously. Also contains Matrixyl 3000 peptide for collagen support. The formula is lightweight, absorbs quickly, and does not feel sticky. Good for all skin types including oily and combination skin. Works well under makeup and SPF.
View on Amazon UK
The Ordinary Hyaluronic Acid 2% + B5
Around 7 on Amazon UK
Contains 2% hyaluronic acid (high and medium molecular weight) with vitamin B5 (panthenol) which enhances the hydrating effect and supports skin repair. Very affordable for the volume you get. The texture is slightly sticky when first applied but absorbs well. Works better on damp skin than dry skin. A solid budget option, though The Inkey List formula is more sophisticated in its use of multiple molecular weights.
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La Roche-Posay Hyalu B5 Serum
Around 24.50 on Amazon UK
Uses two types of hyaluronic acid (high and low molecular weight) with vitamin B5 and madecassoside, an anti-inflammatory compound from centella asiatica. This makes it particularly suitable for sensitive and reactive skin that needs hydration without irritation. The formula is fragrance-free, tested for sensitive skin, and the pump bottle keeps the formula stable. More expensive but more sophisticated than the budget options.
View on Amazon UKHow to use hyaluronic acid correctly
The way you apply it matters significantly. Hyaluronic acid draws water from wherever it can find it. If you apply it to dry skin in a dry room, it will draw water from the deeper layers of the skin, which can actually leave the surface feeling drier.
- Apply to damp skin. Spray your face with water or apply immediately after cleansing while the skin is still damp. The HA has water to draw from and can hydrate the surface effectively.
- Apply on damp skin before moisturiser. Moisturiser acts as an occlusive layer on top, trapping the water that HA has drawn in. Without a moisturiser on top, the water evaporates and the hydration benefit is lost.
- Use it morning and evening. There is no reason to restrict HA to one time of day. It works well in both AM and PM routines.
- Do not use it as your only hydration step. It needs a moisturiser on top to work properly. On its own, it is incomplete.
Important: In very dry climates or during winter when indoor heating reduces humidity, hyaluronic acid can sometimes make skin feel tighter rather than more hydrated. This happens because it draws water from the skin when there is not enough moisture in the environment. If this happens, switch to a more occlusive routine with a richer moisturiser or face oil on top.
Hyaluronic acid and your routine
Hyaluronic acid pairs well with almost every other skincare ingredient. It has no known conflicts with retinol, niacinamide, vitamin C, AHA/BHA acids, or prescription treatments.
The most effective use is:
- In the morning: After cleansing, apply HA to damp skin, wait 60 seconds, then apply your vitamin C serum or niacinamide, followed by moisturiser and SPF.
- In the evening: Apply HA after cleansing on damp skin, then layer your active ingredients (retinol, AHA) on top, and finish with a heavier night moisturiser.
If you have dry skin and want maximum hydration, apply HA before your moisturiser both morning and evening. If you have oily skin, you may only need it in the morning under SPF.
Quick comparison
| Product | HA type | Additional ingredients | Best for | Price |
|---|---|---|---|---|
| The Inkey List HA Serum | 3 molecular weights | Matrixyl 3000 peptide | All skin types | 9.99 |
| La Roche-Posay Hyalu B5 | 2 molecular weights | Vitamin B5, madecassoside | Sensitive, dry skin | 24.50 |
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