Hyaluronic acid and sodium hyaluronate are closely related. They are both star ingredients in skin care products and medical aesthetics, and their core is to provide strong moisturizing ability. But they do have key differences, mainly reflected in their chemical structure, physical properties and practical applications:

I. Core difference: chemical form

• Hyaluronic acid: This is the acidic form of the substance. It is a natural high molecular weight polysaccharide (glycosaminoglycan) composed of repeating disaccharide units (D-glucuronic acid and N-acetylglucosamine). Under physiological conditions (such as in the human body), its carboxylic acid group tends to dissociate into a negatively charged state.

• Sodium hyaluronate: This is the sodium salt form of hyaluronic acid. It is a salt formed by the carboxylic acid group in the hyaluronic acid molecule combined with sodium ions. Simply put, hyaluronic acid + sodium ions = sodium hyaluronate.

II. The main differences caused by the difference in chemical form:

1.Solubility and stability:

• Hyaluronic acid: The molecular weight is very large, and its acidic form has relatively low solubility in water, especially at high concentrations or low pH, and is prone to gel or precipitation. It has relatively poor stability in aqueous solutions.

• Sodium hyaluronate: The sodium salt form makes it extremely water-soluble, and it can easily dissolve in water to form a viscous solution, which is relatively stable even at high concentrations. This is one of the main reasons why it is most commonly used in cosmetic formulations.

2.Molecular weight and viscosity:

• Both have products with different molecular weights (high molecular weight, medium molecular weight, low molecular weight). The larger the molecular weight, the higher the viscosity and the better the moisturizing film-forming property; the smaller the molecular weight, the better the permeability may be.

• At the same molecular weight, sodium hyaluronate can usually form a more stable and higher viscosity solution due to its better solubility.

3.pH value:

• Hyaluronic acid: Its aqueous solution is usually weakly acidic.

• Sodium hyaluronate: Its aqueous solution is usually neutral or weakly alkaline (pH is usually around 6.0-7.5), which is closer to the physiological pH value of the skin and is generally considered to be milder and less irritating to the skin.

4.Hygroscopicity (moisturizing ability):

• The core ability of both is to bind water molecules far exceeding their own weight (up to 1000 times their weight), and they have extremely strong moisture absorption and moisturizing ability.

• In theory, the undissociated carboxyl groups in the hyaluronic acid molecule may have a stronger ability to bind water (hydrogen bonding). However, in practical applications, due to the excellent solubility and stability of sodium hyaluronate, it is easier to reach an effective concentration in the formula and exert a stable moisturizing effect, so its "actual" moisturizing performance is usually better and more reliable.

5.Biocompatibility:

Both have excellent biocompatibility and degradability. Hyaluronic acid exists in the human body itself, so it is usually very safe and has a very low risk of allergies.

III. Emphasis on application:

1.Cosmetics/skin care products:

• Sodium hyaluronate is the absolute mainstream. Because it is easy to dissolve, easy to formulate, highly stable, low in irritation, and has a significant and stable moisturizing effect. The "hyaluronic acid" or "hyaluronic acid" written in the ingredient list of most skin care products (essences, masks, creams, lotions) we see actually almost all refer to sodium hyaluronate (usually marked as Sodium Hyaluronate in the ingredient list). Sometimes sodium hyaluronate of different molecular weights is added at the same time to achieve the effect of surface water lock and deep hydration.

• Pure hyaluronic acid (unsalted form) is rarely used in cosmetic formulas, mainly because of its solubility and stability issues.

2.Medical cosmetology (injection filling):

• Injectable hyaluronic acid products used for soft tissue filling (such as rhinoplasty, lip augmentation, wrinkle filling, and depression filling) are mainly composed of cross-linked hyaluronic acid gel. In order to increase its stability and durability in the body, the hyaluronic acid molecules are chemically cross-linked to form a three-dimensional network structure. Although its raw material is essentially hyaluronic acid, its physical form has undergone tremendous changes during the preparation of the gel, which is completely different from the dissolved state in skin care products.

• The cross-linked gel has support, can maintain its shape, and slowly degrades. Uncross-linked hyaluronic acid or sodium hyaluronate will be quickly absorbed by the body (within a few days) after injection and is not suitable for filling and shaping.

3.Eye drops, joint injections, etc.:

In these areas, both may be used, depending on the product formulation design and the desired properties (such as viscosity, pH, osmotic pressure, etc.). Sodium hyaluronate is also common due to its excellent lubricity and biocompatibility.