Sunday, October 17, 2010

Preservatives: How the heck do they work?

So now that I've sold you on the need for preservatives, how exactly do they work?

Preservatives inactivate the microorganisms in our products in a few different ways, but the primary way is to cause them cause some kind of chemical disruption that leads to death. They leak their internal fluids, they can't maintain pH, their cell walls break open, and so on.

But once the preservative has been used to attack a little beastie, it's used up and can't fight anything else. This is one of the reasons we need to preserve our products at a proper level and why we want to start with as little contamination as possible in our workshop, our ingredients, our equipment, and our packaging!

Preservatives tend to live in the water phase of our products to fight any contamination that might show up in our creations because that's where the beasties live. (They can migrate into the oil phase to fight beasties there, but most our problems are in the water phase!)

We can improve the efficacy of our preservatives by adding propylene glycol, ethanol (alcohol), or glycerine - not only do we get the lovely hygroscopic properties of one of these humectants, but we improve their evil fighting powers! (I do love my double duty ingredients!) Adding a chelating ingredient like citric acid or EDTA to quaterniums, parabens, phenolics, sorbic acid and imidazolidinyl urea also boosts their beastie fighting power!

And there are some ingredients that will interfere with preservatives or inactivate them completely. I'll be writing more about this in the near future, but non-ionic surfactants like polysorbate 80, pigments like ultramarine blue, and thickeners like cellulose derivatives and guar gum are the top ingredients that might interfere with your preservatives! Each preservative type has something that interferes with it and something that can boost it, and it's valuable to know what affects what!

The ideal preservative will be a broad spectrum preservative, meaning it kills off bacteria, mould, yeast, and other fungi. The preservatives we buy are called synergistic preservatives, which are combinations of preservatives intended to eliminate all the various contaminants we could see in our products.

If you take a look at something like Phenonip (INCI: phenoxyethanol, methylparaben, butylparaben, ethylparaben, and propylparaben), you'll see more than one preserving ingredient in the mix. Parabens don't tend to be very good individually, but in combination you've got yourself an awesome broad spectrum preservative.

Or take a look at Liquid Germall Plus (INCI: Propylene Glycol (and) Diazolidinyl Urea (and) Iodopropynyl Butylcarbamate). Diazolidinyl urea on its own is great against bacteria but weak against fungi, while iodopropynyl butylcarbamate is great against yeasts and moulds, so the combination of the two creates a broad spectrum preservative that is slightly boosted by the inclusion of the propylene glycol.

Join me tomorrow as we take a look at the various chemicals we find in our preservatives!


Anonymous said...

When making the scrub, why did you choose to use phenonip instead of germaben plus? Curious. Cheers

Susan Barclay-Nichols said...

Please please please put your name on your comments or I will need to delete it!

I've answered your question in today's Weekend Wonderings! The short answer is that Phenonip is oil soluble and suitable for anhydrous products.

Laura said...

What is the list of preservatives that are not endocrine disruptors like parabens? The reason why I make my products is to avoid additives that are linked to cancer. I understand that mold, bacteria can be an immediate threat, unlike a possibility of cancer, but If I add typical preservatives, I don't see a point in making my own skin care products. What would be a nice balanced approach?

Susan Barclay-Nichols said...

Hi Laura. Welcome to the blog! Take a look at the preservatives section of the blog to learn about the different types of preservatives. As a note, parabens haven't been linked to cancer. If you're referring to the study that came out, there were so many flaws with it, it isn't considered valid. The cancer societies disavow it. (Search for Joe Scearcz's great breakdown if that study and why it was so flawed. Fascinating reading!)

I don't suggest any ingredients that are linked to cancer: I use all the ingredients and products I mention on the blog, and I wouldn't want to share dangerous things with people I love.

Susan Barclay-Nichols said...

Hi Laura. Oops, typo! It's Dr Joe Schwarcz, and you can find his <a href=" on the study that claimed to be about parabens and breast cancer at his blog on CJAD</a>. I really encourage you to take a look at it.

Jodi said...

Hi Susan,
Why do we use preservatives as a percentage of the total volume and not as a percentage of total organic ingredients? Or, as a percentage of the water based ingredients?

June said...
This comment has been removed by the author.
June said...

Dear Susan,
Firstly, thank you very much for the very informative blog! It has really inspired me to look up all the different ingredients and the chemistry behind, and do experiments making my own skincare and cosmetics as well.

I have a question regarding preservatives. As I am in Malaysia, it is sometimes difficult to get supplies, and the only supplier that I can find only sells one type of preservative. Here is the description of said preservative:

"Preserv PE is a paraben free liquid cosmetic preservative with a broad spectrum effect against bacteria, yeasts and mould fungi. Stable to temperature and can be used in pH range up to 12. Preserv PE has limited solubility in water but readily soluble in glycol (Propylene glycol, butylene glycol or propanediol).
INCI: Phenoxyethanol, Ethylhexylglycerin
Recommended use level: 0.5-1%"

My question is, if this preservative has limited solubility in water, and if I'm going to use it primarily in water-based concoctions or lotions, would it still work?

Thank you very much in advance!


A Fajardo said...

Hi Susan, will reheating my lotion that already has a preservative, inactivate it (preservative)?

Susan Barclay-Nichols said...

Hi A! Yes, probably. That's why we don't suggest heating a recipe a second time. The worst part is that you don't know whether it's inactivated or not, so if you add more, you may have too much in a recipe.


hi Susan I m Chirag. Each of your Artical is very very informative and I am learning the science behind each ingredient by reading Your Arrivals..
I am preparing Liquid Dishwash and HandWash. My question is How much preservative in terms of percentages should I use in both these products...currently I am using methyl Paraben and propyl paraben...thanks

Tenli said...

Hi Susan,
I am learning about lotion making and prefer to use natural preservatives as much as possible. I have used Leucidal and so far no problems. I have two questions:
When using a preservative how do you determine the shelf life of the product your making?
For small batches what is a good way to test a product for bacteria without sending it off to a lab? Any good home test kits that are accurate?