Glycerin is a Badass Queen. Here’s Why According to Science!

by | Last updated Sep 17, 2020 | 65 comments

Hi there, friends! I hope you are doing well 🙂

While we’re all patiently waiting for the launch of Malezia (thank you for your patience), I thought it would be a good idea to quickly come on here and answer a question I get asked about EVERY. SINGLE. DAY.

That is….

Is Glycerin Safe for Fungal Acne?

The answer is yes. And I will be explaining all the reasons you should be using it down below!

But first, how do we know it’s not a problem?

Because glycerin is not a fat source and Malassezia is a lipophilic fungus and fatty acid auxotroph. Auxotrophic meaning there is a mutation in one of its genes that prevents it from synthesizing compounds essential for its survival. In this case, those are fatty acids of certain chain lengths which is why it searches for them in the environment. Without them, it cannot live.

“Malassezia are fatty acid auxotrophs, having lost their fatty acid synthetase genes; thus, they require lipids for growth.” (1)

Explained more simply, it’s like a person who doesn’t know how to cook for themselves and relies on Mcdonald’s drive-thru to stay alive. If the zombie apocalypse were to hit tomorrow, you better believe that person is f*cked.

In this scenario, your sebum and fat-containing skincare products are Mcdonalds. Malezia is the apocalypse.

You might be thinking to yourself, “well if Malassezia requires exogenous fats to survive, and glycerin isn’t a fat source, then why does everyone think glycerin is a problem?”

Great question! The answer to that is because I’m an idiot.

Let me explain.

The Conspiracy Against Glycerin: Why Everyone Thinks It’s Growth Promoting.

Perhaps you’ve noticed that flags glycerin as a “high sensitivity” ingredient. That would be my fault.

For those that don’t know, Sezia was based on the original research shared on Simple Skincare Science several years ago. At the time, the only research I could find on glycerin was a single paper whose abstract stated it could promote the growth of malassezia.

I didn’t have access to the full study back then because it’s from China, but prematurely warned everyone on the fungal acne guide to avoid glycerin anyway. That unfortunately snowballed out of control, and now everyone thinks glycerin is the black plague. Sigh.

Fast forward to today, I have read that paper in its entirety thanks to one of our readers (Hailey) who translated it for me and sent it via email. Ironically enough, there was an error in the original translation and the paper actually states:

“Glycerol cannot promote the growth of Malassezia, therefore cannot be used as a susceptibility test… [whereas] the influence of lipids on antifungal activity of drugs must be fully considered.”

In other words, the researchers were examining whether pairing certain ingredients with antifungal drugs reduces their efficacy against malassezia. They found that using fats such as oils and polysorbates makes them less effective. However, the same did not apply to glycerin.

This of course makes sense considering several other sources have had similar findings. For example, Caprilli et al found glycerin does not influence the growth of pityrosporum orbicuIare in culture testing. (2)

Note: pityrosporum is the former name of malassezia.

Additionally, Harding et al found a high glycerol-containing scalp treatment improves dandruff even in the presence of problematic lipids. (3)

Similarly, in a research letter Benaim-Pinto wrote how he healed seborrheic dermatitis (SD) in 18 patients by cleansing with pure glycerin. (4)

Note: both studies above are relevant because malassezia has been implicated in the pathology of dandruff and SD.

Most recently, Dobler et al used two glycerin-containing emulsions as controls to vet ingredients that promote malassezia growth. (5)

And if that wasn’t enough evidence, our super awesome microbiologist and cosmetic chemist has verified glycerin is safe through her own independent testing! 🙂

Why Glycerin Is Amazing for Skin.

Still skeptical? Perhaps you’ve tried glycerin and are convinced it broke you out. If that’s the case, sorry for the breakouts :’(

However, maybe I can convince you to try it out in our urea moisturizer! 🙂 Why would you do such a thing? Because if tolerated glycerin is actually an amazing ingredient with a ton of skin benefits.

For example, did you know that glycerin was the only humectant that was able to restore stratum corneum hydration in AQP3-deficient mice? (6) This may be particularly important for those with dry skin considering AQP3 is a protein that helps facilitate barrier recovery and improve skin elasticity. (7) The other tested molecules that had minimal to no effect included erythritol, xylitol, propanediol, and even urea!

This may be surprising to some considering how much I rave about urea, but it’s not the first time I’ve seen a study with these results. For example, Bettinger et al found that only a moisturizer with 10% glycerin was able to improve skin hydration. The same emulsion made with 10% urea or 10% propylene glycol performed no better than a moisturizer without humectants. (8)

This isn’t to say urea sucks (it absolutely does not – how it’s formulated dictates its performance) but you get the most bang for your buck combining the two. In fact, several studies have demonstrated that urea and glycerin have a synergistic effect, and work better together than either used alone. (9, 10, 11)

One study even showed that combining urea and glycerin has a smoothing effect on the skin! (12)

Fun fact: and now you know why I incorporated glycerin into the urea moisturizer 😉

Other amazing things glycerin does:

  • It reduces erythema a.k.a. skin redness. (13)
  • It retains water in the skin, prevents transepidermal water loss (TEWL), and fights dehydration. (10)
  • It helps exfoliate the skin via desmosomal degradation, which is essentially the ungluing of skin cells so they can slough off. (14)
  • It protects against irritation, environmental stressors, and strengthens the skin barrier against harsh surfactants like Sodium Lauryl Sulfate (SLS). (15, 16, 17)
  • It accelerates skin healing. (10)

And much more! If you want to read a great academic paper that summarizes all things glycerin – check out this PDF.

Closing Remarks

Welp, that summarizes it for this blog post folks! I hope you’ve enjoyed it and have reconsidered giving glycerin a shot…. At least for our urea moisturizer that will be out in a couple months 😉