Glycerin vs hyaluronic acid: two humectants on one label

What "humectant" means in CosIng

The EU's CosIng database lists Glycerin as a humectant and as skin conditioning - humectant, among ten functions¹; Hyaluronic Acid as a humectant, moisturising, skin conditioning and antistatic ingredient²; and Sodium Hyaluronate, its sodium salt, as a humectant and skin conditioning ingredient.³

Those words have set definitions. Humectant means retaining or preserving the moisture in a product during use. Skin conditioning - humectant means increasing the water content of the top layers of the skin, and CosIng adds that humectants are mainly hygroscopic agents, drawing moisture from the surrounding air. Moisturising means increasing the water content of the skin and keeping it soft and smooth.⁴ So part of a humectant's listed job is to keep the product itself from drying out.

A small molecule and a very large one

Glycerin, also called glycerol, is a trihydroxy alcohol⁵ with the formula C3H8O3 and a molecular weight of about 92.⁶ Hyaluronic acid is a polymer, a chain of repeating pairs of two sugars, glucuronic acid and N-acetylglucosamine⁷, and it is far heavier: one laboratory study compared forms of 20-300 kDa with forms of 1,000-1,400 kDa⁸, from about 200 to more than 15,000 times the weight of a glycerin molecule. The sodium hyaluronate page explains what that study found about size.

Both are made by the body. A review of skin hydration describes glycerol as a natural humectant within the stratum corneum, the skin's outer layer, and notes that hyaluronan, long regarded as part of the dermis, is also found in the epidermis.⁹ Another review puts half of the body's hyaluronic acid in the skin.⁷ What a cosmetic applies is a separate matter from what skin makes.

The names on a label

Each name is its own ingredient, with its own entry, from Hydrolyzed Hyaluronic Acid to Sodium Hyaluronate Crosspolymer, and a serum can list several of them. A front label that says "hyaluronic acid" may mean any name in the table: the ingredient list tells you which.

What reviewers concluded

The US Cosmetic Ingredient Review (CIR) panel concluded in 2019 that glycerin is safe as a cosmetic ingredient in the practices of use and concentration described in its assessment.¹⁵ In 2009 it reviewed hyaluronic acid with its sodium and potassium salts, recorded their use as skin conditioning agents at concentrations up to 2%, and concluded they are safe for use in cosmetics as described in that assessment.¹⁶ Both conclusions are about the ingredients as reviewed, not about any one product.

In the EU, neither glycerin nor hyaluronic acid and its salts has an entry of its own in the annexes of the cosmetics regulation, which list substances that are banned, restricted, or permitted as colourants, preservatives or UV filters.¹⁷

Why many formulas list both

A list with both is not necessarily doing one job twice. Glycerin's CosIng functions include solvent and viscosity controlling¹, so it may be there partly to dissolve other ingredients or adjust the texture, roles that hyaluronic acid's listing does not include.²

Humectants are also only one part of a moisturiser. A review of moisturiser technology describes humectants promoting water retention in the stratum corneum while occlusives limit water loss to the air, and notes that products differ in the types and levels of humectants, emollients and occlusives they combine.¹⁸ Another review describes moisturisers as built on occlusive substances, such as Dimethicone, and humectant substances, such as glycerin.¹⁹ The rest of the list matters as much as either name.

On the label

• Glycerin is the EU label name; Glycerine and Glycerol are the same substance.¹
• Hyaluronic acid may be listed as Hyaluronic Acid, Sodium Hyaluronate or any other name in the table, and each counts as a separate ingredient.
• Position: in the EU, ingredients above 1% come first in descending order of weight, and those below 1% may follow in any order.²⁰ With hyaluronic acid recorded at up to 2% when it was reviewed¹⁶, it can sit on either side of that line.
• Size claims such as "low molecular weight" on the front of a pack cannot be checked against the list, because the names carry no molecular weight.
• Read the whole list. Paste it into the skincare ingredient checker to see what each name is listed for, including the occlusives and emollients around the humectants.

Neither name is a verdict on a product. For the rest of a label, see how to read a cosmetic ingredient list.