Hyaluronic Acid: How it works and how to use it

Hyaluronic acid is on the label of almost every serum, moisturiser and sheet mask on the shelf — and for good reason. It is one of the few hydrating ingredients your skin already makes on its own. But its ubiquity has also bred a lot of half-truths: that it "plumps" wrinkles away, that more is always better, or that a single drop will transform dry skin overnight. The reality is more useful than the hype, and it hinges on two things most articles skip: what molecular weight actually means, and how you layer the product.

This guide explains what hyaluronic acid is, how it hydrates skin, why the size of the molecule changes what it does, and — most importantly — how to use it so it works with your skin rather than against it.

What is hyaluronic acid?

Hyaluronic acid (HA), also called hyaluronan, is a glycosaminoglycan — a large sugar molecule — that occurs naturally throughout the body, with a substantial share found in the skin. It is a key molecule for skin moisture, with an unusual capacity to bind and retain water [1]. In the dermis it helps keep the tissue hydrated and cushioned; as we age, the skin’s own HA content and quality decline, which is one reason mature skin looks less plump and holds less moisture.

In skincare, HA is used as a humectant: an ingredient that attracts water and holds it in the upper layers of the skin. That is the whole basis of its hydrating reputation. It does not "feed" the skin or rebuild collagen directly the way a retinoid does — its power is water management, and used correctly that is genuinely valuable.

How hyaluronic acid hydrates the skin

Applied topically, HA works by drawing water toward the skin surface and slowing its loss. A humectant like HA pulls moisture from two sources: from the deeper layers of the skin upward, and — when the surrounding air is humid enough — from the environment. Held in the outer skin, that water makes the surface look smoother, feel softer and appear more supple almost immediately.

There is a catch worth understanding, because it explains most "HA made my skin worse" complaints. In a dry environment — winter heating, air conditioning, low humidity — there is little moisture in the air for HA to grab, so it can draw water from deeper in the skin and, without anything to lock it in, that water simply evaporates. The fix is not to avoid HA but to use it correctly: apply it to damp skin and seal it with a moisturiser. More on that below.

Why molecular weight matters

Not all hyaluronic acid behaves the same, and the reason is molecular weight — the size of the HA chain. This is the single most useful thing to understand about the ingredient, and it is why two products both listing "hyaluronic acid" can perform quite differently.

High-molecular-weight (HMW) HA is a large molecule. Because of its size and water-holding capacity it forms a viscoelastic film on the skin surface that reinforces the barrier and reduces transepidermal water loss, giving an immediate smoothing, cushioned feel — but that same size largely prevents it from diffusing through the stratum corneum, so it stays on top [2]. Low-molecular-weight (LMW) HA is smaller, penetrates more readily, and delivers hydration to deeper layers over a longer period.

Neither is "better" — they do different jobs, which is why many well-formulated products combine several molecular weights to hydrate at multiple levels at once. In a randomised controlled trial, topical 0.1% HA formulations across a range of molecular weights all significantly improved skin hydration and elasticity versus placebo, and the low-molecular-weight versions (50 and 130 kDa) additionally reduced wrinkle depth after 60 days — an effect the authors attributed to LMW HA’s better ability to penetrate [3].

What hyaluronic acid can — and cannot — do

Set expectations correctly and HA rarely disappoints. It reliably improves surface hydration, makes skin look and feel smoother and more supple, softens the appearance of fine lines that are exaggerated by dryness, and supports a comfortable, less tight complexion. Because it is lightweight and oil-free, it does this without heaviness.

What it does not do is permanently "fill" deep wrinkles the way an injectable dermal filler does — topical HA and injected HA are different applications entirely. Nor does it replace a moisturiser: HA attracts water, but it needs an occlusive or emollient layer to keep that water from escaping. Think of it as one specialised step, not a whole routine. Its best results come from consistent daily use as part of a sensible sequence.

How to use hyaluronic acid correctly

Almost every problem people have with HA comes down to application, not the ingredient. Two habits make the difference.

Apply to damp skin. HA works best when there is water available to bind. After cleansing (or after a hydrating toner or essence), apply your HA serum while the skin is still slightly damp, not bone dry. This gives the humectant moisture to hold onto at the surface.

Always seal it in. This is the step most people miss. Immediately after the HA has been applied, follow with a moisturiser to lock the water in place. Without that occlusive layer — especially in dry or heated air — the water HA is holding can evaporate and leave skin feeling tighter than before. The serum attracts the water; the cream keeps it there.

Beyond those two rules: HA layers comfortably with most other actives, which is part of its appeal. It pairs well with vitamin C in the morning and can help buffer the dryness that stronger actives like retinoids can cause in the evening. As always, introduce one new product at a time so you can tell how your skin responds.

How to choose by skin type

One of HA’s biggest strengths is how broadly it suits different skin.

Oily and blemish-prone skin. HA is ideal here precisely because it hydrates without oil. Oily skin still needs water, and a lightweight HA serum under a non-comedogenic moisturiser delivers hydration without a heavy, pore-clogging feel.

Dry and mature skin. HA is a natural fit, but the sealing step is non-negotiable — pair it with a richer, barrier-supporting moisturiser to hold the water in. A blend of molecular weights, or an HA serum layered under a lipid-rich cream, tends to give the most comfortable result.

Sensitive and reactive skin. HA is generally very well tolerated, since it mirrors a substance the skin already makes. Choose fragrance-free formulas and keep the routine simple.

Skin under active treatment. During courses of retinoids, peels or in-clinic procedures, skin is often drier and more reactive; a simple HA serum sealed with a gentle moisturiser is a low-risk way to restore comfort.

The Ph.Doctor approach to hydration

Ph.Doctor is a dermocosmetics line developed by Dr. Nina Wiśniewska and biotechnologist Anna Sienkiewicz, built on a "less is more" philosophy: few ingredients, each with a defined function. For hydration, two products map neatly onto the two rules above — a serum that carries hyaluronic acid into the skin, and a lipid cream that seals it in.

The serum is the Tetra C Serum, which pairs a stable vitamin C with a well-tolerated form of hyaluronic acid.

Tetra C Serum is, per its product card, "a synergy of 3 ingredients: Vitamin C + crocus extract + non-inflammable form of hyaluronic acid." The card describes that HA form — "Epidermosil is a combination of low-molecular hyaluronic acid and silanetriol" — which "nullifies the possible pro-inflammatory effects of hyaluronic acid," has "an effect on faster epidermal regeneration," and is "more effective in epidermal regeneration than hyaluronic acid alone." The serum overall "moisturizes, evens out skin tone, lightens hyperpigmentation and has an anti-aging effect," is "88% ingredients of natural origin," is vegan and "suitable for pregnant and breastfeeding women." Usage follows the damp-skin, then-moisturiser logic above: "apply 3 to 5 drops to the face and neck in the morning and evening. Once the product is absorbed, use a Ph.Doctor moisturizer."

That moisturiser step is where the Lipid facial cream comes in — the occlusive, barrier-supporting layer that keeps the hydration from escaping.

Lipid facial cream is described on its card as "a universal cosmetic. Suitable for all skin types, including those sensitive or temporarily sensitized by dermatological therapies." It uses "niacinamide," which "strengthens the epidermal barrier," alongside "squalane and rice oil," so "the skin regenerates faster." Per the card’s tested results, it "reduced TEWL by 34% after 4 weeks of use" — TEWL being "the natural evaporation of water from the epidermis, which affects skin dryness" — which is exactly the water-loss that a humectant like HA needs sealed in. It is "89% natural ingredients," vegan, fragrance-free and "suitable for pregnant and breastfeeding women," and is listed as suitable "during dermatological treatments: retinoids, peels, laser."

Used together the logic is simple and matches the science: the serum brings water-binding HA (plus antioxidant vitamin C) into slightly damp skin, and the lipid cream seals it in and reduces the water loss that would otherwise undo it.

Frequently asked questions

How often can I use hyaluronic acid?

Daily, morning and evening, for most people. HA is gentle and mirrors a substance the skin already produces, so it does not require the cautious "start slow" build-up that stronger actives do. The key is not frequency but technique — apply it to damp skin and always seal it with a moisturiser.

Should I apply hyaluronic acid to dry or damp skin?

Damp. HA is a humectant, so it works best when there is water available to bind. Apply it after cleansing while the skin is still slightly moist, or after a hydrating toner or essence. On completely dry skin in a dry environment, HA has less surface water to hold and can feel less effective.

What is the difference between low- and high-molecular-weight hyaluronic acid?

It comes down to the size of the molecule. High-molecular-weight HA is large, stays on the surface, forms a smoothing film and reduces water loss. Low-molecular-weight HA is smaller, penetrates more readily and hydrates deeper layers over time. Neither is better — many products combine several weights to hydrate at multiple levels, and in trials low-molecular-weight HA has also been linked to reduced wrinkle depth.

Can hyaluronic acid dry out my skin?

It can if used incorrectly. In dry air, a humectant with no moisture to draw from can pull water from deeper in the skin, and without an occlusive layer that water evaporates, leaving skin tighter. This is entirely preventable: apply HA to damp skin and follow immediately with a moisturiser to lock the water in.

Can I combine hyaluronic acid with retinol or vitamin C?

Yes — HA pairs well with both. It sits comfortably alongside vitamin C in the morning and can help buffer the dryness that retinoids sometimes cause in the evening, which is one reason it is such a useful base layer. Introduce one new product at a time so you can judge how your skin reacts.

Is hyaluronic acid suitable for oily or blemish-prone skin?

Very much so. Oily skin still needs hydration, and HA provides it without adding oil or heaviness. A lightweight HA serum under a non-comedogenic moisturiser hydrates without contributing to clogged pores, which makes it one of the most universally suitable hydrating ingredients.

Do I really need a moisturiser after hyaluronic acid?

Yes, and it is the step that makes HA work. The serum attracts and holds water; the moisturiser seals it in and slows its evaporation. Skipping it — particularly in heated or air-conditioned rooms — is the most common reason people feel HA "did nothing" or even left skin drier.

Hyaluronic acid in a serum or in a cream — which is better?

They serve different roles. A serum delivers a higher concentration of HA in a lightweight base and is applied first, to damp skin. A cream generally provides the sealing, barrier-supporting layer on top. The most effective approach is usually to use both in sequence rather than to pick one.

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Selected references

1. Papakonstantinou E, Roth M, Karakiulakis G. Hyaluronic acid: a key molecule in skin aging. Dermatoendocrinol. 2012;4(3):253–258. Reviews HA as the key molecule in skin moisture, with a unique capacity for retaining water, and its decline with skin aging.
2. Zanchetta C, Scandolera A, Reynaud R. Hyaluronic acid in topical applications: the various forms and biological effects of a hero molecule in the cosmetics industry. Biomolecules. 2025;15(12):1656. High-molecular-weight HA forms a viscoelastic surface film that reinforces the barrier and reduces transepidermal water loss but does not readily penetrate the stratum corneum; lower molecular weights penetrate more.
3. Pavicic T, Gauglitz GG, Lersch P, Schwach-Abdellaoui K, Malle B, Korting HC, Farwick M. Efficacy of cream-based novel formulations of hyaluronic acid of different molecular weights in anti-wrinkle treatment. J Drugs Dermatol. 2011;10(9):990–1000. RCT: topical 0.1% HA of various molecular weights significantly improved skin hydration and elasticity; the 50 and 130 kDa (low-molecular-weight) groups significantly reduced wrinkle depth after 60 days.