Preservatives are essential, particularly if you’re working with water or liquid based formulas. But even a cake mascara needs a preservative because you introduce moisture to it when you swipe across it. I hope this overview will explain why preservatives are so critical and convince you to preserve your products properly.

What exactly do preservatives do? They help prevent the growth of microbes like bacteria and fungi in our products, which can make us ill, cause separation of our emulsion or product, and cause “off” smells and appearances (mold is pretty distinctive). Once a product becomes contaminated, it’s dangerous, and there have been reports of contact dermatitis and worse from using unpreserved products.

We use preservatives whenever we work with products that contains water. Even sterilizing your water first or using distilled water isn’t good enough; you must use a preservative. Anhydrous, or pure oil and butter products, do not typically need preservatives because they do not contain water or other liquids. The exception to this is sugar and salt scrubs, which need a preservative even though they are anhydrous, because one will be reaching into them with wet fingers and introducing water to the product that way. It’s a possible recipe for disaster without a good preservative.

Furthermore, simply refrigerating your water containing products isn’t enough. It may buy you time, but we are talking mere days, not weeks or months, and in the case of lotion or sugar scrub, who really wants to apply that to the body ice cold out of the fridge? Besides, once it is contaminated-and it WILL get that way without a preservative-the pathogens have been there, lurking, for much longer than you could see or smell or otherwise detect them. Isn’t that an appealing thought? To slather yourself with moldy lotion? No? Then use a broad spectrum preservative!

Ok, it’s like this. Sometime in your life, probably as a teen or young adult, you sat down a cup of some kind of beverage and then your room got messy and you forgot about it. For days, or maybe even weeks. Do you remember what that cup looked like when you cleaned up and found it? What was growing inside? Would you feel comfortable drinking it or adding those contents to your products? Because without a preservative, that’s what you’re doing. You’re setting your product up to slowly become a scary science fair experiment.

So let’s talk about how preservatives 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 microbe, 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 pathogens live. (They can migrate into the oil phase to fight microbes there, but most our problems are in the water phase!)
We can improve the efficacy of our preservatives by adding 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! Adding a chelating ingredient like citric acid or EDTA to quaterniums, parabens, phenolics, sorbic acid and imidazolidinyl urea also boosts their fighting power!
And there are some ingredients that will interfere with preservatives or inactivate them completely. Pay attention to non-ionic surfactants like polysorbate 80, pigments like ultramarine blue, and thickeners like cellulose derivatives and guar gum as 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 (my personal favorite) 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.

How to choose a preservative:

So we’ve spent some time getting to know our preservatives, so let’s take a look at what preservatives we might want to use and those we should avoid when creating our products.

Let’s say you’re making a scented body spray and you want to use polysorbate 20 to emulsify your fragrance into the water based product. Which preservative is right for this product? We know the parabens like Phenonip, Liquipar PE, and Germaben II are partially deactivated by polysorbate 20, so we might want to choose something else (say Liquid Germall Plus or Optiphen). I’d have the same problem with something like my foaming post-crafting hand wash because I use the polysorbate 20 to emulsify the d-Limonene.
Or let’s say you want to make a moisturizing body wash with olive oil to help chase away winter dryness. If you’re using polysorbate 80 to emulsify that oil, use non-paraben based preservative.
If you’re interested in making a cream with titanium dioxide (say a liquid foundation) again the parabens are right out of the question because they can be deactivated by the pigments and the titanium dioxide.
And make sure you aren’t using hydroxypropylmethyl cellulose to thicken your anionic systems – shampoo, body wash, face wash – when using something containing phenoxyethanol based preservatives like Optiphen, Optiphen ND, Phenonip, Liquipar Optima, or Liquipar PE.
If you’re making anhydrous products you want to preserve – like sugar scrubs – you’ll want to choose preservatives that are oil soluble, meaning the parabens like Phenonip and so on.

List of most common preservatives

So you can choose the one that’s best for you.

Cosmocil CQ
Geogard Ultra
Germaben II
Liquid Germall Plus
Liquipar Oil
Liquipar Optima
Liquipar PE
Optiphen ND
Optiphen Plus
Suttocide A
Tinosan SDC

And a big shout out to Susan at Point of Interest blog for all the information.