Glycerin in Skincare: What the Studies Show

The research on glycerin says one thing clearly: it is among the most effective humectants in skincare, raising the water content of the skin's outer layer more reliably than most alternatives. Studies also show that its effect builds with regular use and lingers after you stop. Here is what the main studies found, in plain language, and what they mean for the products on your shelf.

How glycerin moisturizes

Glycerin, or glycerol, is a simple molecule with three hydroxyl groups, and those groups bond with water. Applied to skin, it pulls water into the stratum corneum, the outer layer, from the air and from the layers of skin beneath. It is also one of the compounds in the skin's own natural moisturizing factor, the mix of substances skin makes to keep itself supple.

Glycerin was first described by a Swedish chemist in 1779. What has changed since is not the ingredient but the amount of research behind it, and newer work suggests it does more than hold water. It helps keep the fluid between skin cells in balance, neither too dilute nor too concentrated, and it supports the orderly shedding of the outermost cells, which keeps skin smooth rather than flaky.

How it compares with other humectants

Several head-to-head studies put glycerin at or near the top. A 2016 study described it as the most effective humectant for raising hydration in the top layer of skin, when compared against a range of others, including lactic and glycolic acids. In a separate comparison, 10% glycerin outperformed both 10% propylene glycol and 10% urea for skin hydration over three hours.

A 2005 study found that the level of glycerin in the skin tracks closely with how hydrated the skin is: more glycerin, better hydrated skin. That is a tidy result, and it fits with everything else in the literature.

The reservoir study

The most useful single study for everyday skincare compared moisturizers in 394 people with dry skin. Two high-glycerin moisturizers, at 25% and 40% glycerin, were tested against 16 popular moisturizers that contained less than 6%. The two high-glycerin formulas hydrated faster and better.

More interesting was what happened after people stopped. Skin that had been using the high-glycerin moisturizers stayed hydrated for longer than skin that had used the others. Researchers call this a reservoir effect: glycerin that has moved into the outer layer of skin keeps working for a while, rather than disappearing with the next wash.

How much glycerin a formula needs

Glycerin starts to help at around 3%, and the benefit for dry skin increases with concentration, up to about 20 to 40%. Around 10% is often described as a sweet spot: enough for clear moisturizing and comfort, while the formula still feels light rather than sticky. Very high levels make a product feel tacky, which is the trade-off formulators balance.

Labels rarely state percentages, so the order on an ingredient list is the best clue you have. Ingredients are listed from most to least, and glycerin near the top usually means a meaningful amount.

Glycerin and the skin barrier

Studies suggest glycerin does more than add water. Laboratory models of the skin's outer lipids show that glycerin keeps those lipids from stiffening in low humidity, which helps explain why glycerin creams feel so good on skin in winter or in heated rooms. Other research links glycerin with a sturdier, more stable outer layer that loses less water.

One study of a fluid combining glycerin, hyaluronic acid and centella asiatica in healthy women found a hydrating effect lasting up to 24 hours from a single daily application, along with better barrier function. The broader point holds across the research: glycerin works well alone and even better alongside complementary ingredients.

Glycerin and hyaluronic acid together

Both are humectants, but they work a little differently. Glycerin is a very small molecule that moves into the outer layer of skin. The hyaluronic acid used in most serums is far larger and mostly hydrates the surface, which gives that immediate dewy, plump look. A formula that uses both covers both effects. Our Vitamin C Collagen Boosting Face Serum with Niacinamide is one example: glycerin and sodium hyaluronate sit alongside aloe and cucumber, with ethyl ascorbic acid and niacinamide to help skin look brighter and more even.

Safety in the research

Glycerin has one of the cleanest safety records of any cosmetic ingredient. Research describes it as non-toxic, non-irritating and non-sensitizing, and the Cosmetic Ingredient Review Expert Panel has concluded it is safe as used in cosmetics. It does not clog pores, so it suits oily and acne-prone skin as well as dry and sensitive skin.

What the research means in practice

Regular use matters more than any single application, because the reservoir effect builds over days. And because glycerin draws water in rather than sealing it, it works best under something that holds that water in place: an oil, a butter or a cream. Our Hydrating Hand Cream and Rejuvenating Body Cream are built that way, with glycerin and aloe leaf juice for water and Kalahari melon seed, jojoba, avocado and argan oils to keep it there.

Questions about the glycerin research

How much glycerin does a product need to work?

Studies show benefits from about 3%, with more for dry skin at higher levels. Around 10% is often cited as the best balance of moisture and a light, non-sticky feel.

What is the reservoir effect?

In a study of 394 people with dry skin, those using high-glycerin moisturizers stayed hydrated longer after they stopped. Glycerin that has moved into the outer layer keeps holding water for a while.

Is glycerin better than hyaluronic acid?

Neither is simply better. Glycerin is smaller and moves into the outer layer of skin, while hyaluronic acid mostly hydrates the surface, so formulas that use both cover more ground.