One of the most common questions we get here on Chemists Corner about formulating is what preservative to use. Before I go into a long explanation about how this is a complicated question, here’s a quick answer.
What preservative should I use? – short answer
Use a paraben like Methylparaben or Propylparaben, a formaldehyde donor like DMDM Hydantoin or Imidazolidinyl Urea or both types.
These have been safely used for years and are compatible with a large number of different formula types. If product safety is your number one concern, following this advice will work true in the vast majority of your formulations.
How do decide what preservative to use – longer answer
Of course, these days things are much more complicated than product safety. When trying to decide what is the best preservative to use that answer depends on numerous factors such as
- Formula type
- Ingredients in the formula
- Cost tolerance
- Raw material quality
- Manufacturing conditions
- Consumer behavior
- Marketing position
- Where product will be sold
You can’t really answer the question of what is the best preservative to use without more information.
What are you allowed to use?
Governments have regulations on the type and amount of preservative you can use. These limitations are different whether you’re selling in the US, Canada, EU, Japan or other places around the world. And in the US, there are also states that have attempted to regulate the preservatives you’re allowed to use. The first thing you have to know to figure out the best preservative is what is legally allowed. You do this by checking the cosmetic regulations that affect you.
In addition to government regulations, the store where you want to sell your product may have limitations on what you’re allowed to use. Whole Foods has a specific list of banned ingredients for cosmetic products and many of these are preservatives. Also, your brand marketing position or your consumers’ biases may prevent you from using specific preservatives.
When figuring out what the “best” preservative to use, figure out what you are allowed to use first.
What type of formula are you making?
The next factor in deciding what is the best preservative is identifying the product type.
Is the product meant to be left on the body? Some preservatives are fine to use when the product is going to be rinsed off (e.g. Methylisothiazolinone . Other preservatives are better for products left on the skin because they don’t cause allergic reactions.
Is the product anhydrous or does it contain a large amount of water? For many anhydrous systems, you may not have to include a preservative. Microbes require some source of water to grow so they don’t usually grow in anhydrous systems. However, I recommend including preservatives even in anhydrous formulas because water can get in the product during use which could lead to problems of contamination.
What type of ingredients are you using?
The type of ingredients in your formula will be an important factor in what preservative will be the “best” for your formula. For example, parabens are not compatible with certain proteins. Organic acid preservatives are not compatible with cationic and some nonionic materials. Xanthan gum, Lecithin, cellulose gums, can inactivate certain preservatives. Kaolin, Titanium Dioxide and Silica can tie up preservatives and make them less effectives. Natural ingredients can contribute to microbial growth so you’ll need extra preservation than you might otherwise.
What are your cost constraints?
Since preservatives add cost to your formula this is another thing you have to consider when deciding what is the “best” preservative. If you’re looking for a functional, formaldehyde free, paraben free, natural preservative, that’s going to cost much more than a standard preservative.
What type of packaging are you using?
Product packaging can also influence your preservative choice. If you’re using a screw cap tub you’ll need a more robust preservative system than if you are using a pump product.
What are your manufacturing conditions?
The best preservative will also depend on the type of manufacturing conditions you have. Sometimes in production facilities they develop house biofilms inside the manufacturing lines. Theses things can be particularly stubborn and cause contamination to any type of formula. If you are working with equipment that has one of these biofilms, you’ll need a preservative that will not only prevent this contamination but also prevent general contamination of your product.
Best cosmetic preservatives
All this is to say that there is no simple answer to the question, what is the “best” preservative for my system. If you want to know what preservative to use, you’ll need to learn about cosmetic preservatives, what ones work in what systems, what ones are allowed in your market and a myriad of other bits of information about your particular situation.