Hyaluronic acid: what it is and how it works

Hyaluronic acid: what it is, how it works and why it matters for your skin

Hyaluronic acid (HA) is a glycosaminoglycan—a type of polysaccharide—that the human body produces naturally. It is found in the skin, joints, eyes and connective tissue, where it performs functions of hydration, lubrication and structural support. In the skin, approximately 50% of the body's total HA is concentrated in the dermis and epidermis, where it forms a three-dimensional network that maintains moisture and gives volume to the tissue.

What makes this molecule special is its hygroscopic capacity: a single hyaluronic acid molecule can attract and retain up to 1,000 times its weight in water. That property is the basis for both cosmetic serums and injectable dermal fillers. If you are looking for information about specific commercial brands of HA fillers, consult our guide at /blogs/marcas-de-acido-hialuronico.

In summary

• Hyaluronic acid is a natural polysaccharide present in skin, joints and eyes, capable of retaining up to 1,000 times its weight in water.
• There are three categories by molecular weight: high (superficial hydration), low (deep penetration) and cross-linked (injectables with prolonged duration).
• Natural HA production decreases progressively from age 25 onwards, contributing to dryness, volume loss and wrinkle formation.
• Topical HA hydrates the outer layers of the skin; injectable HA restores volume, fills wrinkles or improves skin quality from within.
• Skinboosters and biomodulators represent a distinct category of HA injectables designed to improve skin quality, not to add volume.

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What is hyaluronic acid at the molecular level

Hyaluronic acid is a linear polymer composed of repetitive units of D-glucuronic acid and N-acetyl-D-glucosamine. Unlike other glycosaminoglycans, it does not bind to a central protein: it is synthesized directly on the cell membrane by enzymes called hyaluronic acid synthases (HAS1, HAS2 and HAS3). Each produces chains of different length and molecular weight.

Its chemical structure gives it a strong negative charge that attracts water molecules, forming a viscous and elastic gel. In the human body of an adult weighing approximately 70 kg, there are approximately 15 g of HA in the form of sodium hyaluronate, and about one-third of that total is degraded and renewed each day.

Where HA is found in the body

Hyaluronic acid is present in virtually all vertebrate tissues, with especially high concentrations in three areas:

• Skin: Contains approximately 50% of total body HA. In the dermis it is part of the extracellular matrix along with collagen and elastin, providing structural support and hydration. In the epidermis it contributes to the regulation of cell proliferation.
• Joints: In synovial fluid, HA of very high molecular weight (6,000–7,000 kDa) acts as a lubricant and shock absorber, reducing friction between joint surfaces.
• Eyes: The vitreous humor is largely composed of HA, which maintains the shape of the eyeball and its transparency.

Types of hyaluronic acid by molecular weight

The molecular weight of HA determines its biological properties and clinical applications. It is classified into three broad categories:

High molecular weight (> 1,000 kDa)

Long HA chains form a film on the skin surface that retains water and protects the epidermal barrier. These are the ones that predominate in serums and moisturizing creams. They do not penetrate the skin significantly, but provide immediate hydration in the outermost layers and a temporary smoothing effect.

Low molecular weight (< 500 kDa)

Shorter chains can penetrate deeper layers of the epidermis. At the biological level, low molecular weight HA fragments have distinct properties: they activate cellular responses such as fibroblast stimulation and collagen production. They are common in high-concentration dermatological serums designed for deeper action.

Cross-linked HA

Cross-linked HA is manufactured through a chemical process that links hyaluronic chains with a cross-linking agent—generally BDDE (1,4-butanediol diglycidyl ether). This cross-linking creates a cohesive gel that resists enzymatic degradation, allowing the product to remain in the tissue for months instead of hours or days.

Injectable dermal fillers use cross-linked HA. The combination of chains of different molecular weights and different degrees of cross-linking is what allows designing products with specific properties: some softer for lips or fine lines, others firmer for cheeks or chin. For a detailed analysis of HA filler brands and families, visit /blogs/marcas-de-acido-hialuronico.

Topical hyaluronic acid: serums and creams

Topical products with HA function as humectants: they attract water from the environment and from the deeper layers of the skin towards the surface. Their efficacy depends on several factors:

• Concentration: Most studies show benefits with concentrations between 0.1% and 2%. Very high concentrations are not necessarily better and can generate a tight feeling when dry.
• Molecular weight: The most effective products combine HA of high and low molecular weight to hydrate both superficial and deeper layers simultaneously.
• Formulation: HA works best when applied to damp skin and sealed with an occlusive moisturizer. In very dry climates, without occlusion, HA can draw water from the dermis to the surface, where it evaporates, producing the opposite effect from what is desired.
• Sodium hyaluronate vs. hyaluronic acid: In cosmetics, most products use sodium hyaluronate (the sodium salt of HA), which is more stable and soluble.

Topical HA improves surface hydration, luminosity and texture, but cannot restore lost volume or fill deep wrinkles.

How to combine topical HA with other actives

Topical hyaluronic acid is one of the most versatile ingredients because it is compatible with most cosmetic actives:

• HA + vitamin C: An effective combination for your morning routine. Vitamin C provides antioxidant protection and luminosity; HA provides hydration. Apply vitamin C serum first, then HA serum, and seal with sunscreen.
• HA + retinol / retinoids: HA helps counteract the dryness and irritation that usually accompany retinol use. Apply the retinoid on dry skin, followed by HA serum as a hydrating layer. This combination is especially useful during the first weeks of retinol adaptation.
• HA + niacinamide: Both ingredients are compatible and hydrating. Niacinamide strengthens the skin barrier and reduces sebum production, while HA provides hydration. They can be used in the same routine without conflict.

The general order of application is: cleanser → active (vitamin C or retinoid) → HA serum → occlusive moisturizer → sunscreen (morning).

Injectable hyaluronic acid

Injectable HA allows placing the product directly in the dermis or subcutaneous tissue, achieving effects that topicals cannot reach. It is divided into two broad categories according to its objective:

Dermal fillers

HA fillers are cross-linked gels designed to restore volume, reshape facial contours or fill folds and wrinkles. Each product has a specific formulation—degree of cross-linking, HA concentration, particle size—that makes it more suitable for certain areas and objectives.

For example, a firm and cohesive filler is ideal for projecting the chin or defining the mandibular angle, while a soft and fluid gel works better on lips or perioral lines. Duration varies between 6 and 24 months depending on the product, the area treated and individual metabolism.

A key advantage of injectable HA versus other filler materials is its reversibility: the enzyme hyaluronidase can dissolve the product in case of complications or unsatisfactory results.

For a complete guide on dermal fillers, including indications and what to expect, consult /blogs/fillers-todo-lo-que-necesitas-saber.

Skinboosters and biomodulators

Skinboosters and biomodulators are HA injectables whose objective is not to add volume or reshape, but to improve skin quality from within: deep hydration, luminosity, elasticity and firmness.

• Skinboosters: They use HA with low degree of cross-linking or micro-drops of stabilized gel that distribute homogeneously in the superficial dermis. They are injected at multiple points with micropapule or microdeposit technique. Products such as Restylane Skinbooster and Skinvive (Juvéderm) belong to this category.
• Biomodulators: Profhilo is the best known example. It contains high and low molecular weight HA without conventional chemical cross-linking, linked through a patented thermal process. It is injected at five strategic points on each side of the face (BAP technique: Bio Aesthetic Points). The HA diffuses through the tissue and stimulates the production of collagen, elastin and adipocytes, achieving a skin remodeling effect beyond simple hydration.

The usual protocol for skinboosters and biomodulators consists of two to three initial sessions separated by two to four weeks, followed by maintenance sessions every four to six months. Results are cumulative: the skin progressively improves in luminosity, texture and firmness.

Hyaluronic acid and aging

HA production decreases progressively with age. The concentration in the skin goes from approximately 0.33 mg/g of wet tissue in young skin to 0.15 mg/g at age 60 and 0.07 mg/g at age 75. This decline is due to several mechanisms:

• Reduced HAS activity: The HAS1 and HAS2 enzymes, mainly responsible for HA synthesis in the dermis, reduce their activity with chronological aging.
• Fewer fibroblasts: With age, the quantity and function of dermal fibroblasts decreases, which reduces the production of HA, collagen and elastin.
• Ultraviolet damage: UV radiation decreases the expression of HAS1 and HAS2 in the dermis, while increasing the activity of hyaluronidases, the enzymes that degrade HA. This accelerates the loss of dermal HA, a process known as photoaging.
• Changes in distribution: In young skin, HA is distributed homogeneously forming a continuous network connected to collagen and elastin fibers. In aged skin, this network becomes fragmented, and HA deposits disappear from the intercellular and pericellular spaces of the dermis.

The clinical consequence of this loss is visible: the skin loses turgidity, hydration and volume, becomes thinner and wrinkles and sagging appear.

HA and health regulation

HA products, especially injectables, are subject to strict health regulation. The main agencies that oversee their approval include:

• FDA (United States): Approves HA fillers as medical devices. Each product must demonstrate safety and efficacy in clinical trials.
• COFEPRIS (Mexico): Regulates the importation, marketing and use of injectable medical devices, including HA fillers.
• EMA / AEMPS (Europe): HA fillers require CE marking as medical devices.
• ANVISA (Brazil) and INVIMA (Colombia): Apply similar regulations in their respective markets.

Only products with current regulatory approval should be used, and their injectable application must be performed exclusively by a trained physician. Products without regulation, purchased outside authorized medical channels, represent a significant risk of complications.

Difference between topical and injectable hyaluronic acid

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Frequently asked questions

What is hyaluronic acid and what is it used for?

Hyaluronic acid is a natural polysaccharide produced by the body that retains water and gives volume to tissues. It is found in the skin, joints and eyes. In aesthetic medicine it is used topically in cosmetics to hydrate the skin surface, and injected as a dermal filler to restore volume and treat wrinkles, or as a skinbooster to improve overall skin quality. Its ability to retain up to 1,000 times its weight in water makes it one of the most widely used ingredients in both dermatology and cosmetics.

Is hyaluronic acid natural or artificial?

Hyaluronic acid is a molecule that the body produces naturally. However, the HA used in cosmetics and injectables is manufactured industrially through bacterial fermentation (usually from Streptococcus strains). This allows obtaining a biocompatible high-purity product. Being identical in structure to the human molecule, the risk of allergic reactions is very low, although like any injectable procedure, it is not without possible side effects.

How many types of hyaluronic acid are there?

They are classified primarily by molecular weight: high (> 1,000 kDa), low (< 500 kDa) and cross-linked. High molecular weight hydrates the surface without penetrating deeply. Low molecular weight can reach deeper layers of the epidermis and stimulate cellular processes. Cross-linked is used in injectable fillers because it resists enzymatic degradation, remaining in the tissue for months. Each type has specific applications, and many products combine different molecular weights to optimize results.

What is the difference between topical and injectable hyaluronic acid?

Topical HA hydrates the outer layers of the skin by attracting and retaining water on the surface, but cannot restore volume or fill deep wrinkles. Injectable HA is placed directly in the dermis or subcutaneous tissue, which allows restoring lost volume, reshaping facial contours or improving skin quality at a deep level. They are complementary tools, not substitutes: topical is part of a daily skincare routine, while injectable is a medical treatment with more lasting and structural results.

At what age does hyaluronic acid start to decrease?

HA production begins to decline gradually from the mid-twenties. The concentration in the skin goes from 0.33 mg/g in young skin to 0.15 mg/g at age 60 and barely 0.07 mg/g at age 75. This decline is progressive and is accelerated by accumulated sun exposure, which damages the enzymes responsible for its synthesis. That is why daily sun protection is one of the most effective strategies to preserve natural HA levels in the skin.

What are skinboosters?

Skinboosters are injectable hyaluronic acid products with low degree of cross-linking designed to improve deep hydration and skin quality, not to add volume. They are injected in micro-drops distributed homogeneously in the superficial dermis. Products such as Restylane Skinbooster and Skinvive (Juvéderm) are representative examples. The usual protocol includes two to three initial sessions separated by two to four weeks, with maintenance every four to six months. Results include greater luminosity, hydration and more uniform texture.

What is Profhilo and how does it differ from a filler?

Profhilo is an injectable biomodulator containing high and low molecular weight HA without conventional chemical cross-linking, linked through a patented thermal process. Unlike a filler, it does not add volume or reshape contours: it diffuses through the dermis stimulating the production of collagen, elastin and adipocytes. It is injected at five strategic points per side of the face. The result is an overall improvement in firmness, elasticity and luminosity. It is especially useful for treating mild sagging and loss of skin quality that do not require volumetric filling.

Can injectable hyaluronic acid be dissolved?

Yes. One of the main advantages of injectable HA is its reversibility. The enzyme hyaluronidase can degrade and dissolve cross-linked HA gel. This resource is used in case of unsatisfactory results, overcorrection or vascular complications. Hyaluronidase acts by breaking the polymer bonds, restoring the tissue to its previous state. This is not possible with other permanent or semi-permanent filler materials, which makes HA one of the safest options for dermal filler procedures.

Does hyaluronic acid make your face fat?

No. Injectable hyaluronic acid restores or adds volume in a localized and controlled way only in the areas where it is applied. It does not produce weight gain or generalized inflammation. The perception of "puffy face" is usually due to excessive application or inadequate technique, not the product itself. An experienced physician applies conservative amounts distributed harmoniously to achieve natural results. Skinboosters, for their part, do not add any visible volume.

How long does the effect of hyaluronic acid last?

Duration depends on the type of product and the area treated. Topical HA requires daily reapplication, as its hydrating effect is temporary (hours). Injectable dermal fillers last between 6 and 24 months depending on the formulation, degree of cross-linking, anatomical area and individual metabolism. Skinboosters and biomodulators maintain their effect between four and six months per treatment cycle, although the cumulative benefits on skin quality extend with periodic maintenance sessions.

Is hyaluronic acid safe?

Injectable HA has a favorable safety profile when using products approved by regulatory agencies (FDA, COFEPRIS, EMA) and the application is performed by a trained physician. The most common side effects are mild and transitory: redness, swelling and bruising at the injection sites. Serious complications, such as vascular occlusion, are rare but possible, and require a physician trained in prevention and management of these situations. Products without health registration should never be used nor should they be applied by non-medical personnel.

Does oral hyaluronic acid work?

There is clinical evidence that oral hyaluronic acid supplements (120–240 mg/day) can improve skin hydration and skin texture after 2 to 8 weeks of consistent use. Studies show modest but measurable improvements in stratum corneum hydration and reduction of fine wrinkles. Oral HA is also used as an adjunct in patients with joint discomfort. However, the effects are significantly less than those of injectable HA, and cannot restore volume or treat deep wrinkles. Oral HA is a reasonable complement within a comprehensive skin care strategy, not a substitute for topical or injectable treatments.

Does hyaluronic acid help with dark circles?

Injectable HA can improve dark circles caused by volume loss in the tear trough area, filling the depression that creates the dark shadow. However, this is an anatomically complex area, with very thin and vascularized skin, which requires a physician with specific experience and appropriate low-concentration, high-hydrophilicity products. Not all dark circles benefit from injectable HA: those caused by hyperpigmentation or visible blood vessels require other approaches.