Propanediol
Propanediol · INCI Propanediol
Some ingredients you choose. Some arrive because they came in the bottle with something else. Propanediol is the second kind, and when we sat down to write about it we assumed there would be nothing to say. We were wrong, and the correction is worth reading.
We did not choose it. It arrived with the chlorella. Then we looked properly at what it does, and it turns out to be doing more than carrying things.
What it is
Propanediol is a clear liquid made by fermentation. It is in our formulas because our chlorella active is supplied as a liquid, and propanediol is about a third of that liquid: it dissolves the algal compounds, keeps them stable and keeps the bottle free of microbes. Take it away and there is no chlorella to add. That is how it got here, and for a while it was the only thing we thought it was doing.
It does two other things, and both of them touch your skin. It is a genuine humectant, which means it attracts water and holds it in the skin's surface, in much the same way glycerin does but with a lighter feel. And it is a penetration enhancer, which means it makes the outer skin a little more willing to let water-loving ingredients through. That second one is quietly useful in a formula like ours, where several of the ingredients that matter are water-soluble and need to reach somewhere to be worth anything.
One thing worth knowing, since the two get muddled. Propanediol is not propylene glycol. They sound alike, they are different molecules, and propanediol is the gentler of the two.
What it does in our formulas
Three things. Only one of them relates to the chlorella active
It holds water in the skin
Propanediol is a genuine humectant. It attracts water and holds on to it, in the same way glycerin does, with a lighter and less tacky feel. This is a real benefit to your skin, and we had been describing it as an afterthought, which was wrong.
Well characterisedIt helps the other ingredients through
Propanediol is a well-documented penetration enhancer: it makes the skin's surface more willing to let water-loving ingredients pass. In a formula like ours, that matters, because several of our water-soluble ingredients need to get somewhere to be of any use. The propanediol is part of how they do.
Well characterisedIt carries the chlorella
The reason it is in the formula at all. Our chlorella active is supplied as a liquid, and propanediol is about a third of it: it dissolves the algal compounds and keeps that bottle free of microbes before it ever reaches our workshop.
Well characterisedWhat the research does not show
Propanediol takes it from both directions: condemned as a nasty chemical by one crowd, oversold as a hydrating active by another. Both are wrong.
Marketed as A harsh synthetic chemical, or the same thing as propylene glycol
Marketed as A microbiome-friendly preservative
So: a fermentation-derived carrier that holds water in your skin and helps the rest of the formula get where it is going. Less glamorous than an oil, and considerably more useful than we first gave it credit for.
On the label and in the range
Propanediol appears in every one of our formulations at around three tenths of a percent, which is why it sits where it does in the list. If you have wondered why a name you do not recognise ranks above ingredients you do, this is your answer: our chlorella active is largely propanediol, and every part of it is declared. The exact percentage is published on each product page.
Is it suitable for me?
Propanediol has a good safety record and is well tolerated on sensitive skin. Within our chlorella active it is certified vegan by the Vegan Society and approved under the COSMOS and NATRUE organic standards. It is made by fermentation rather than from petroleum, and it carries no restrictions under UK or EU cosmetic law.
As with anything new, if your skin reacts easily it is worth patch testing first.
The research behind this page
We review the published literature. We do not conduct the studies below.
- ALGAKTIV S.L. (Barcelona). ALGAKTIV BioSKN Product Information Dossier, v2024.0, and technical efficacy dossier. Manufacturer data, unpublished. Sponsor-generated. →
- Fiume MM, et al. Safety Assessment of Propanediol as Used in Cosmetics. Cosmetic Ingredient Review. Int J Toxicol. →
- Pinto D, Ciardiello T, Franzoni M, Pasini F, Giuliani G, Rinaldi F. Effect of commonly used cosmetic preservatives on skin resident microflora dynamics. Sci Rep 2021;11:8695. (Industry-funded; peer-reviewed. Cited in the teardown as a finding we decline to claim.) →