Glycerin: the dullest ingredient in your routine, and the one doing the most

Look at the ingredient list of almost anything in your bathroom. Glycerin is usually in the top five, often second or third, right after water.

Nobody puts it on the front of the bottle. It is cheap, it has been used for over a century, and there is no story to tell about rare botanicals or breakthrough technology. It is also one of the best-evidenced ingredients in skincare, and the reason a lot of products feel as good as they do.

What it does

Glycerin is a humectant: it binds water and holds it in the upper layers of the skin. Your skin makes its own humectants, collectively called natural moisturising factors, and glycerin behaves much like them.

Two things make it unusually good at this.

It is small, so it moves into the upper layers rather than sitting on top. And it does more than hold water there: research shows it also helps the skin barrier mature properly and supports the enzymes that let dead cells shed on schedule. That is why skin that gets enough glycerin feels smooth rather than just damp.

The catch, and it is the same one

Like every humectant, glycerin pulls water from wherever it can get it. In dry air, with nothing sealing it in, it can draw moisture up from deeper in your skin, where it then evaporates.

In practice this is much less of a problem than with pure hyaluronic acid, because glycerin is almost never used on its own. It sits in formulas alongside oils, emollients and lipids that hold the water in. But the rule still applies: put something over it. The article on hyaluronic acid goes into that mechanism.

Why nobody markets it

There are three reasons and none of them is about how well it works.

• It costs almost nothing. Hard to justify a premium on an ingredient that is a commodity.
• It has no origin story. Most cosmetic glycerin comes from vegetable oils, which is accurate and unglamorous.
• It has been around too long. New ingredients get attention; a hundred-year-old one does not.

The practical consequence for you: when you compare two products and one costs four times as much, check how far apart they really are in the first five ingredients. Often the answer is not very.

How much is a good amount?

Most well-made moisturisers sit somewhere between 3 and 10 per cent. Below about 3 per cent it is doing little; much above 10 and the texture starts to feel sticky.

You cannot read the number off a label, but position tells you something. Glycerin in the top three means a meaningful amount. Glycerin near the end, after the preservatives, means a trace.

Where ours sits

Glycerin is in six of our seven formulas, usually second or third on the list. In Milky Miracle it is one of the three ingredients we highlight, because a cleansing milk that exfoliates with glycolic acid and gluconolactone needs something holding water in the skin while it works. That is the whole reason the format is a milk rather than a foam.

In Hydration Hero it works alongside hyaluronic acid, panthenol and a xylitol complex, with Ceramide NP and squalane to keep what they attract.

Frequently asked questions

Is glycerin bad for oily skin?

No. It contains no oil, does not clog pores, and oily skin is often dehydrated anyway. A light glycerin-based gel is usually more comfortable than a rich cream.

Can I put pure glycerin on my face?

Better not. Undiluted glycerin is sticky and, in dry air, is exactly the situation where it pulls water out of your skin. In a formula it is diluted and balanced with other ingredients.

Is vegetable glycerin better than synthetic?

The molecule is identical either way, and your skin cannot tell the difference. Most cosmetic glycerin is plant-derived, which is a sourcing question rather than a performance one.

Does it work in winter?

Yes, provided you seal it. In cold, dry air a humectant on its own struggles, which is when a richer cream on top matters most.

Sources

• Fluhr JW, Darlenski R, Surber C, Glycerol and the skin: holistic approach to its origin and functions, British Journal of Dermatology, 2008.
• Milani M, Sparavigna A, The 24-hour skin hydration and barrier function effects of a hyaluronic acid, glycerin, shea butter formulation, Clinical, Cosmetic and Investigational Dermatology, 2017.