The best cosmetic preservatives

At Chemists Corner, one of the most frequent questions we get is from people looking for the best cosmetic preservative to use for their formula. This is a complicated question and really depends on many factors. But, before we dive into what preservatives you should consider, let’s step back and review why you need preservatives in the first place.

There are two primary reasons you need preservatives:

  1. To stop microbes from spoiling your products.
  2. To stop microbes from causing disease.

The microbes that can infect your formulas primarily include bacteria, mold, and yeast. In small quantities they don’t represent much of a problem but when they multiply, look out. Bacteria like Pseudomonas can cause health problems including skin and eye infections, toxic shock, strep throat, and even food poisoning. Yeast like Candida albicans can cause thrush. And many other bacteria can cause your products to smell bad, change color or otherwise break down (this is what cosmetic stability testing is for). 

What factors impact the preservative you should use?

While product safety is the most factor to consider when identifying the best preservative system for your formula, there are other factors to take into account such as:

  • Formula type
  • Ingredients in the formula
  • Cost tolerance
  • Packaging
  • Raw material quality
  • Manufacturing conditions
  • Consumer behavior / benefit
  • Marketing position
  • Regulations and retailer requirements

Let’s dig into this list a little deeper…

What type of formula are you making?

Is the product meant to be left on the body?  Some preservatives like Methylisothiazolinones are fine to use when the product is going to be rinsed off, but shouldn’t be used on leave-on products due to sensitization issues. Other preservatives like parabens are best for products left on the skin because they don’t generally cause bad 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, you may want to include preservatives even in anhydrous formulas because water can get in 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. Organic acids can be sensitive to light so you’ll want to consider opaque packaging as opposed to clear.

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. These 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.

 

Regulations and preservatives

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 impact you. Here is a list of the leading regulatory bodies around the world:

 

In addition to government regulations, the retailer where you sell your product may have limitations on what you’re allowed to use. In the US, retailers such as Whole Foods and Credo have lists of banned ingredients that you need to be aware of. Even retailers like Target, Walmart and Sephora have ingredient restrictions if you want to position your products as clean or natural. These lists vary by retailer and region so it’s important to be aware of these guidelines during the formulation process. Also, your brand marketing position or your consumers’ biases may prevent you from using specific preservatives.

Types of preservatives

Parabens

Parabens are the most widely used preservatives. In fact, they actually occur in nature, being found in low levels in carrots, cucumbers and mangos. They are derivatives of p-hydroxybenzoic acid and go by names like Methylparaben, Propylparaben, and Butylparaben. They are typically supplied as powders and can sometimes be difficult to incorporate into a system due to the water solubility limitations. In terms of functionality, they are good at killing fungi (mold & yeast) and have some weak activity against gram negative bacteria. They aren’t as effective against bacteria as they are against fungi.

Parabens have suffered from poor public perception due to misinformation. While there is some evidence that they are a weak hormone disruptor, the levels used in cosmetics have never been demonstrated to have that effect. Also, there was a study published in 2005 that implied a concern between paraben use and breast cancer but the paper was retracted and there was never any link established. However, that didn’t prevent some marketers and NGO groups from vilifying the ingredient. The SCCS, which is an independent science group out of the EU, looked at the scientific safety evidence for parabens and validated their safe use as did regulatory bodies in the US and Japan. 

Formulation notes:

  • Optimal pH range: 3.5 – 8.0
  • Compatibility
    • Low water solubility for straight parabens
    • Salt versions are highly water soluble 
    • Varying oil solubility
  • Typical use range: 0.1 – 0.4%
  • Used in a wide range of products from leave-on to rinse off including body lotions, hair products, color cosmetics, lip products, and skincare products.

Formaldehyde donors (FD)

Formaldehyde derivatives are the next most common preservative. These compounds interfere with membrane proteins which kill microbes. Bad press and real safety concerns have led cosmetic chemists to stop using formaldehyde. Instead ingredients that dissociate into formaldehyde when put in a water solution are used. These are compounds like DMDM Hydantoin, Imidazolidinyl Urea, and Gluteraldehyde. As far as effectiveness, they have a broad spectrum of activity but are most effective against bacteria. They also have a good antifungal effect but many formulators will include a separate fungicide when formulating with these preservatives. It should be noted that formaldehyde donors vary in their effectiveness.

Formaldehyde donors also suffer from poor perception issues. Just the name formaldehyde is a scary ingredient to consumers so this has limited the use of these robust preservatives. FD’s are known skin allergens so this can limit the use for some applications. 

Formulation notes:

  • Optimal pH range: 3.0 - 10
  • Compatibility
    • Highly soluble in water
    • FD can be slightly soluble in oils
    • Reacts with proteins
    • Can react with Avobenzone
    • Poor heat stability
  • Typical use range: 0.1 – 0.8%
  • Given allergen and skin sensitivity concerns, FD’s are better for rinse-off products like shampoo and body wash as opposed to leave-on products (ie lotions). 

Isothiazolones

Synthetic compounds like Methylchloro- Isothiazolinone and Methyl-Isothiazolinone are effective at incredibly low levels. They have been shown to work at a wide range of pHs and in many different formulas. They are suitable to use when you want to make a paraben free or formaldehyde donor free formula. 

Their use has been stymied however, by at least one study that suggested they could cause skin sensitization (roughly 2-3% of the population). In the EU there has been a ban on the use of isothiazolones for leave-on products and a strict limitation for rinse-off products.

Formulation notes:

  • Optimal pH range: 2.0 – 9.0
  • Compatibility 
    • Water soluble
    • Compatible with nonionics, emulsifiers, surfactants 
  • Use range: 7.5 – 15ppm (roughly 0.0015%)
  • Primarily used in rinse-off products such as body wash, shampoos and conditioners given concerns with skin sensitivity.

Alternative preservatives 

If you are like many formulators and trying to avoid parabens, formaldehyde donors and anything else that doesn’t seem “natural” your options are more limited. Still, there are a variety of compounds that can be used as preservatives, but you’ll face more limitations in terms of efficacy.

Phenol derivatives

Phenol derivatives have been used in cosmetics for many years with the most common example being Phenoxyethanol. This has become a popular choice among formulators looking for alternatives to parabens and FD’s.  Unfortunately, it’s not as effective as traditional preservatives so its use is limited. 

Phenoxyethanol has a broad spectrum effect, but it is a weak biocide and fungicide. It’s very good against pseudomonas. For this reason it is mostly used with a combination of preservatives. The way the ingredient kills cells is that it disrupts the cell membrane, causing a leakage of the cell contents which results in cell death. By using things like glycols you can make the phenoxyethanol even more effective.  

Formulation notes:

  • Optimal pH range: 3.0 – 10.0
  • Compatibility
    • Low solubility in water
    • Compatible with nonionics & proteins
    • Can sometimes reduce viscosity
    • Heat stable
    • Has a slight odor which can impact overall scent of product and interact with your fragrance 
  • Typical use range: 0.4 – 1.0%
  • Used in a range of rinse-off and leave-on products though often in conjunction with other preservatives/ingredients to improve efficacy.

Organic Acids and their salts

Ingredients in this class demonstrate low toxicity and are approved for most natural standards, making them a popular choice for formulators looking to adhere to natural and clean restrictions from retailers like Whole Foods, etc. Examples include:

  • Benzoic Acid
  • Sodium Benzoate
  • Sorbic Acid
  • Potassium Sorbate
  • Dehydroacetic Acid
  • Sodium Dehydroacetate
  • Salicylic Acid 

They occur in nature but the versions of these ingredients that are used in the cosmetic industry do not come from plants - they are synthesized in the lab to create nature identical versions. That is not to say you can’t get the all natural version of these ingredients but for most people it would be cost prohibitive. 

There are formulation challenges with these preservatives and they also can be irritating (they are acids) and at least some of them like sorbic acid can result in possible allergic reactions to some people.

Formulation notes:

  • Optimal pH range: most activity below 5.0
  • Compatibility
    • Low solubility in water
    • Incompatible with cationics, some proteins, nonionics
    • Can be light sensitive
    • Can cause discoloration
  • Typical use range: 0.2 – 0.5%
  • Used in a wide range of products but primarily rinse-off formulas like body wash and shampoo.

Quats

Compounds that contain nitrogen and have a positive charge when placed in solution are called quaternary compounds (or quats). Many of them demonstrate an ability to kill microbes. This includes ingredients like Benzalkonium Chloride, Methylbenzethonium chloride, and Benzethonium chloride. Their cationic nature makes them less compatible with anionic surfactants which limits their application and use.

Alcohol

Ethanol is a great preservative but you need to use it in high levels and it faces significant environmental restrictions. Other compounds like benzyl alcohol, dichlorobenzyl alcohol, and even propylene glycol all have some anti-microbial effect. In lower levels, these compounds are less effective at preserving products.

More alternatives 

The most common alternatives include Phenoxyethanol, Organic acids (like benzoic or sorbic acid), Benzyl alcohol, coupled with boosters like Caprylyl Glycol. Additional options include:

 

  • Boraxitrus seed extracts
  • Copper salts
  • Fragrance oils
  • Glycerin
  • Hinokitiol
  • Honey
  • Japanese Honeysuckle extracts
  • Melaleucol (Tea Tree) oil
  • Perillic acid
  • Pyridine derivatives like Sodium pyrithione and zinc pyrithione are used to kill the bacteria that causes dandruff
  • Salt
  • Silver Chloride
  • Sodium Gluconate
  • Sugar
  • Usnic acid
  • Wasabi extract
  • Zinc Salts

How do you optimize preservative efficacy?

When evaluating formulas, you’ll often notice that products use more than one preservative. You’ll also notice ingredients like chelating agents used in combination with preservative systems. The reason for this is simple - some single preservatives do not kill a large enough range of microorganisms.  As a cosmetic formulator you need to ensure that your preservative system will kill any bacterial, mold, or fungi that the formula might encounter.  Since you don’t know what will be encountered you have to plan for every possibility (or at least as many as you can).

There are some preservatives that are able to kill a wide range of microbes (e.g. Alcohol, Parabens, Formaldehyde donors). That is why these ingredients are so popular with formulators.  Other ingredients like Sodium Benzoate or Potassium Sorbate are only effective against certain types of microbes. They are more active against yeasts and molds but have a lower activity against bacteria. One way to compensate for the ineffectiveness of one compound is to include another compound that has the ability to kill other organisms.  By combining preservatives, you increase the spectrum of microbes that your formula can withstand.

Synergistic preservative ingredients

In addition to using multiple preservatives, some ingredients can provide a synergistic effect, allowing you to use lower levels of preservatives which can decrease the toxicity potential (and cost) while providing increased efficacy.

Here is a list of ingredients that can improve the effectiveness of preservative systems:

  • Acids, alkalis
  • Alcohols (e.g. Ethyl, isopropyl, benzyl)
  • Cationic surfactant (e.g. Benzalkonium chloride, cetyl pyridinium chloride)
  • Anionic surfactants (e.g. Soap, sodium lauryl sulfate)
  • Esters (e.g. Glyceryl monolaurate, sucrose hexadecanoate)
  • Humectants (e.g. Glycerin, propylene glycol, butylenes glycol, sorbitol, caprylyl
  • glycol, ethylhexylglycerin, 1,2-hexanediol)
  • Aqueous solutes (e.g. Sugars, dextrins, salts)
  • Phenolic antioxidants (e.g. t-butyl hydroxyanisole [BHA] and t-butyl
  • hydroxytoluene [BHT])
  • Botanicals (e.g. Tea tree oil, tannins)
  • Chelating agents (e.g. Citric acid, tetrasodium EDTA, sodium etidronate)
  • Colors
  • Fragrances and flavors

Conclusion

The most important thing to remember is that your formula MUST be adequately preserved. It’s good to try out new, alternative preservatives but understand that you are taking a risk. The alternative preservative may not work as well, may break down over time, and may have some unknown health risks.

References: 

Brannan, Daniel K. Ed., Cosmetic Microbiology: A Practical Handbook. CRC Press , Boca Raton, FL., 1997. Chapter 2.

Handbook of Cosmetic Science and Technology. Marcel Dekker, Inc., New York, NY, 2001. Chapter 21

January 24, 2022
Copyright 2021 © ELEMENT 44 INC BY, PERRY ROMANOWSKI
Chemists Corner

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