Hyaluronic Acid

Hyaluronic acid is a glycosaminoglycan, a long sugar-based molecule that occurs naturally throughout the body. Skin holds a large share of it, mostly in the dermis, where it sits between the collagen and elastin fibres and keeps that space hydrated and cushioned. Levels fall with age and with sun exposure, which is part of why mature skin can look flatter and less plump.

On an ingredients list it appears in several forms. Sodium Hyaluronate is the salt form and is the one most commonly used, being more stable and easier to formulate with. You may also see Hydrolysed Hyaluronic Acid, Sodium Hyaluronate Crosspolymer or references to low, medium and high molecular weight. These are the same basic molecule cut to different sizes, and the size matters more than the name.

Larger molecules stay on the surface, holding water there and giving an immediate smooth, plumped look that washes off. Smaller fragments travel a little further into the upper layers and hydrate from slightly deeper down, with an effect that builds rather than appearing instantly. Many serums now include a blend precisely so that both happen.

It is a humectant rather than a moisturiser in the everyday sense: it attracts and holds water but does nothing to stop that water leaving again. That single fact governs almost all the practical advice about how to use it.

It also causes a persistent confusion worth clearing up. The hyaluronic acid in an injectable filler and the hyaluronic acid in a serum are the same family of molecule used in entirely different ways. A filler is placed into the skin in a cross-linked gel form to add volume in a specific place. A serum sits on the surface and hydrates the upper layers. A topical product cannot reproduce what an injectable does, and any product suggesting otherwise is overstating its case.

Hyaluronic acid works by binding water. Its molecular structure holds a very large amount of water relative to its own weight, and when it is applied to skin it draws moisture in and keeps it in place within the upper layers. Hydrated skin looks smoother and fuller, and fine lines that are partly the result of dehydration look softer. This is a physical effect on water content, not a change to the skin’s structure.

Where that water comes from depends on the conditions around you. In humid air, a humectant pulls moisture from the atmosphere. In dry air, particularly in heated rooms, on aeroplanes or in cold weather, there is little atmospheric moisture available, so it can instead draw water up from deeper in the skin. If nothing is applied on top to seal that in, the water evaporates and skin can end up feeling tighter than before. This is the single most common reason people report that hyaluronic acid made their skin drier.

The practical answer is straightforward. Apply it onto skin that is still slightly damp so there is water available to bind, then follow with a moisturiser containing occlusive or emollient ingredients to hold everything in place. Used that way it is one of the most reliable and least troublesome ingredients in skincare, and it suits every skin type because it adds water rather than oil.

Hyaluronic acid is simple to use, but it depends entirely on what happens immediately after you apply it.

• Apply to damp skin. Straight after cleansing, or after a mist or toner, while skin is still slightly wet. Onto bone-dry skin in a dry room it has far less to work with.
• Always seal it. Follow within a minute or two with a moisturiser. A humectant with nothing over the top is an unfinished step.
• Order in the routine: one of the first things after cleansing. Thin, watery layers go before creams, oils and SPF.
• When: morning and night, as often as you like. There is no tolerance to build and no break needed.
• Pairs well with: everything. It is particularly useful alongside retinoids and exfoliating acids, where added hydration makes the adjustment period easier.
• In dry or heated environments: be stricter about sealing it. In genuinely arid conditions some people do better with a richer cream and less reliance on humectants alone.
• Percentages are not the point. Above roughly 2% these serums start to feel tacky rather than work better. Molecular weight and the surrounding formula matter more than the number.
• Under makeup: let it settle for a minute before the next layer, or products can pill.

The hydrating effect is real but not cumulative in the way an active is. Skip it for a week and skin returns to its baseline.