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How to Prevent Contamination in Cosmetic Products

This recent article about scientists discovering bacteria living in hairspray provides a good example of why cosmetic products need to be preserved. Microbes can grow almost anywhere! And these tiny organisms bring with them some distasteful product changes or even disease. As a cosmetic chemist it’s up to you to formulate properly and keep these invaders at bay. You typically do that by adding preservatives to your formulas. Unfortunately, you’ll have to know more than just the science as preservatives are some of the most highly regulated and restricted ingredients you will use.

Why you need cosmetic preservatives

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 all kinds of 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 awful, change color or otherwise break down. (This is what stability testing is for).

The following is a list of common preservatives used in cosmetic and personal care products. As a future (or current) formulator, you will undoubtedly be using many of them.


Parabens are the most commonly used preservatives. 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. They are effective against a broad spectrum of bacteria and fungi. They do have pH limitations and are not effective against all microbes so you usually will need an additional preservative.

Formaldehyde donors

Formaldehyde derivatives are the next most common preservative. These compounds interfere with membrane proteins which kills microbes. They are effective against bacteria, fungi, and mold. 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. They are most often used in surfactant systems.

Phenol derivatives

Phenol derivatives have been used in cosmetics for many years and can be effective against a range of microbes. Unfortunately, they are not as effective as the previous ingredients so their use is limited. The most common examples is Phenoxyethanol.


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 include ingredients like Benzalkonium Chlroide, Methene aommonium chloride, and Benzethonium chloride. Their cationic nature makes them less compatible with anionic surfactants which limits their application & use.


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.


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. There use has been stymied however, by at least one study that suggested it could cause skin sensitization.

Organic Acids & Others

Various other compounds are used as preservatives but all face some limitations not experienced to the same extent as the previous ingredients discussed. Some of the most important include Sodium Benzoate, Chloracetamide, Triclosan, and Iodopropynyl Butylcarbamate. Pyridine derivatives like Sodium pyrithione and zinc pyrithione are used to kill the bacteria that causes dandruff.

Why cosmetic preservatives are vilified

More than any other ingredient, preservatives are most often called out as the worst ingredients you can use in a formula. Even people who know nothing about chemistry have likely heard about the “evil” parabens and formaldehyde.

Preservatives are designed to kill cells. That’s why they are effective. Unfortunately, that’s also why they are potentially hazardous. They don’t easily discriminate between good human cells and bad microbial cells. But ultimately, the risk from using preservatives is significantly lower than that of using unpreserved cosmetics. There are safe levels of “toxic” chemicals. All chemicals can be deadly if you’re exposed to a high enough level. How many people die from water exposure (e.g. drowning)?

Remember, it’s the dose the matters!

To be sure, cosmetic science research is ongoing in the field of preservatives since many things previously deemed safe have been reclassified as hazardous. Suppliers who can come up with even safer preservatives will likely make a lot of money. Hopefully, they’ll do it soon but there do not appear to be any promising materials on the horizon.

{ 50 comments… add one }

  • Samar 02/23/2015, 9:54 am

    If I want to make natural organic cosmetics product for sell them ,what is the most safe preservative should I use to have safe product and how I know it’s expiry date?

    • Perry Romanowski 03/09/2015, 8:44 pm

      That really depends on the type of product you are making and the raw materials you are using.

  • amy myers 01/14/2015, 11:12 pm

    I haven’t seen any comments regarding aspen bark as a preservative. Any thoughts?

    • Perry Romanowski 01/20/2015, 9:58 am

      It’s not effective enough to use as your primary preservative.

  • asmil 10/18/2014, 10:29 pm

    Hi, perry.. please explain why my product ( sunblock & toner) in few months become moldy?

    • Perry Romanowski 10/20/2014, 8:52 am

      Most likely because whoever put the formula together didn’t use an effective preservative.

  • Melissa 10/09/2014, 2:45 pm

    If your raw ingredients for cosmetics have bacteria (whether growing or stable), is there a way to kill the bacteria or stop the bacteria from growing? If you heat the ingredients up for an extended period of time, will that do the trick?

    • Perry Romanowski 10/09/2014, 2:49 pm

      Heating the ingredient for an extended time can work but it can also damage the ingredient. If you know that something has bacterial growth I wouldn’t use it.

  • Pete 07/07/2014, 11:28 pm

    I’m not a chemist, so this might be a totally stupid question. But if you use preservatives that convert into formaldehyde, how is that different from using formaldehyde in the first place?

    • Perry Romanowski 07/14/2014, 11:12 am

      You use a lot less formaldehyde.

  • hoaduocthao 06/28/2014, 10:18 pm

    Can you show me the interaction between chemical agents in cosmetics
    Many thanks

    • Perry Romanowski 06/29/2014, 3:49 pm

      I don’t know what you mean. What specific interaction do you want to know about?

  • Erica 04/26/2014, 1:43 pm

    What are your thoughts on Leucidal Liquid? It’s tough out here in the natural world. I would much rather send out a product that is safe, but with so much information out there, many consumers seem to ignore the whole “preservatives are needed”. I would love to be able to tell them the real scoop on the “natural” preservatives so that my products don’t get frowned upon when they are safely made.

    • Perry Romanowski 05/01/2014, 10:21 am

      Hello Erica – That preservative can work in some systems but it does not have a broad spectrum of activity so I’d be skeptical that if you just use it that your formulas will be effectively preserved.

      • Erica 05/13/2014, 1:58 pm

        They weren’t! In my lighter lotions, mold formed rather quickly, even though I used the recommended amounts. Thank goodness for testing. What a mess that would have been. As always, thanks for the great blog!

  • AG 04/06/2014, 1:07 pm

    Hi Perry! Thanks for the great article, as always! I hope you don’t mind commenting on a preservative mystery. One of my friends was looking at a product (I believe a face moisturizer) that contained seven different parabens, and she asked me why it might need so many different kinds. I’m used to seeing perhaps two to four parabens in a formula. Unfortunately I don’t know the product or the specific ingredients. Would you mind sharing your thoughts on why so many different parabens might have been required for the preservative system?

    • Perry Romanowski 04/08/2014, 12:38 pm

      That many is probably not required but the cosmetic chemist who originally put the formula together probably just used a blend containing all of those. In theory, more paraben types will kill more types of microbes. The other thing is that the manufacturing facilities might not have been clean enough and they needed additional preservative to prevent contamination.

      • AG 04/10/2014, 4:08 pm

        Thank you for the interesting and unexpected answer! I never considered that the environment in which products are made might affect the chemist’s decisions. I really appreciate you taking the time to share your thoughts!

  • Dr. Vineet Sharma 04/02/2014, 1:17 am

    Can anyone suggest me ZPTO compatible preservatives, preferably other than DMDM and Isothiazolinones.

    • Perry Romanowski 04/02/2014, 1:43 pm

      What do you mean by ZPTO? I’m unfamiliar with the abbreviation. It also depends on what else is in the formula.

  • Stuart 11/02/2012, 7:03 am

    Hi there.
    I was told that potassium sorbate and sorbic acid are excellent preservatives for the use in skin care products. Is that correct or are there some better working alternatives? Can I use Vitamin C for instance to have a better position for my adverts?

    • Perry 11/02/2012, 7:09 am

      I would not say that they are excellent preservatives. Those would be the parabens. But potassium sorbate and sorbic acid can be good enough. It does limit your formulation ability however. You can add vitamin C to your formula but it is not a preservative.

      • Phil 10/30/2013, 6:15 am

        Sorbic and benzoic acids are, by themselves, pretty poor cosmetic preservatives.

        • Perry Romanowski 10/31/2013, 7:05 pm


  • Christine 11/17/2011, 11:46 pm

    Hi Perry. Concerning preservatives, can you give a list of the popular types of preservatives that the ‘all natural’ community do use? I am trying to appeal to that market, and I am aware that they have to turn to some synthetics etc but unsure of which ones. Thanks in advance

  • Ruby 11/05/2011, 10:15 am

    Can anyone recommend a vegetarian microbial test kit that can be used to test for contamination? Thanks.

    • stan Idelsen 02/09/2013, 3:58 pm

      yes the Koko test of Shulk (Microcount) is excellent !

      • Phil 10/30/2013, 6:15 am

        vegetarian? what do you mean?

  • Liliana 10/27/2011, 8:31 am

    Thank you for the exciting topic and useful information!
    More than anyone I’m interested in understanding how do you, chemists, decide which preservative system fits your needs and how much of it you need to use. Our company has long experience with natural preservatives in the food industry (we have a patent on rosemary preservative for foodstuffs). Based on this know-how, we developped cosmetic preservatives from rosemary, olive leaves, pomegranate and even onion extract. All challenge tests (US Pharmacopoeia) show excellent anti-microbial activity. The main problem is price. Phenoxyethanol for example costs <4$/kg (which is around 8$/pound) and the prices of our products are higher. How much should a 100% natural preservative cost? The dosage we recommend is 0,25 – 0,5%. Also, some of these preservatives have a color (for ex. pomegranate is reddish), is this a nogo?

    Thank you very much for your help :)

    • Perry 10/27/2011, 9:31 am

      Hello Liliana – Very good questions.

      The primary considerations in picking a preservative are (in no particular order)…
      1. Effectiveness
      2. Formula compatibility
      3. Price
      4. Marketing story

      Of these, price is probably the smallest factor as the preservative usually doesn’t add much to the overall cost of the formula. It would matter if the price got too high however. It sounds like your preservatives would have some niche application because color and odor effects are a problem. In my opinion, the current preservatives work and have no real problems associated with them. Indeed there is a push from some areas of the market to have “all natural” preservatives but for cost and compatibility reasons I doubt the market for alternative preservatives will ever get too large.

    • laura 02/15/2015, 1:18 am

      Liliana, does your company sell the preservatives you described?
      Please share if that’s ok. Thanks, Laura

  • LaNita Darden 05/26/2011, 11:01 am

    Yes, I would like recommendations on this also.

  • ratna 05/24/2011, 3:43 pm

    what are the process to avoid the contamination during manufacturing of cosmetic products!!!!?

  • LaNita Darden 05/03/2011, 1:31 pm

    Naturagard Ultraâ„¢ which is Gluconolactone (and) Sodium Benzoate. What can you tell me of this? It is considered an ECOCERT certified preservative. Will this do the job for amore natural preservative?

  • Perry 01/10/2011, 7:23 pm


    Oil soluble preservatives inhibit growth of microbes at the interface of the oil and water.

  • Prajakta Bhuskute 01/10/2011, 2:13 am

    Please Explain the mode of action of oil soluble preservatives.
    If they are not soluble in aquas phase how do they prevent microbial attack in emulsions.

  • David Steinberg 10/04/2010, 7:53 am

    I am always amazed about the use on non-preservative preservatives. Why? When I ask companies who offer these, why don’t you register them and get approved in the EU and Japan. The responds is usally,the cost of all the safety testing. Duh! Preservatives or any other chemical with cidal properities are bioloigically active. So safety must be done.

    People are so interested in using preservatives which have very limited safety and no peer review, instead of preservatives which have undergone extentisve testing and reviews.

    Why? Usually marketing. “If I don’t know it can’t hurt me”. Nonsense.

  • Hamish 10/04/2010, 6:18 am

    Hi Perry,

    Just in relation to article about traditional preservatives and you mentioned there was no promise of any other new materials on the horizon. I would like to mention that we have been doing some very successful production with Dr Straetmans preservative systems of glyceryl caprylate, and p ansinic acid. There are also some other nature identicals like Mackaderm GCP and various systems from Lonza. There is also some other manufacturers based here in Australia who have developed some successful systems as well, though questionable is they are in use in full production scale? Preservation is not something that we tread around lightly either, being a contract manufacturer certainly brings on more challenges than expected. Another point you don’t seem to talk about is water quality. We’ve dabbled in several systems and find our current system to be the best yet, based on ozone. I would enjoy finding out more about reducing water activity as mentioned by David, this is something i have read about in the book he mentioned and think this could be something of benefit in the future with more “natural” options other than glycerine. Another question is, do you know much about the method of milling and product preservation? Aparently it’s and older system that was used in the food industry years ago and has apparently been attempted in the cosmetic industry

  • Michael 05/05/2010, 5:50 am

    We test with 2000ppm MI in aqua. I do not know what the pH is, and the number of positives is a part of the manuscript and therefore confidential at the moment.

  • David Steinberg 04/29/2010, 7:28 am

    What level of MI is in your test? What vehicle? What pH?
    What number of positives compared to other allergens?

  • Michael 04/29/2010, 3:26 am

    It is correct when David Steinberg states that the test kit use the mixture with the chloro and non-chloro. However, in the last years methylisothiazolinone alone has also been part of the contact allergy test at the Hospital where I work, and upcoming scientific articles will reveal that methy-isothiazolinone contact allergy is relatively frequent.

    This is not a recommendation to discard isothiazolinones or other allergenic preservatives; they are a necessity but should be used with caution.

  • David Steinberg 04/24/2010, 3:05 pm

    Isothiazolinone is not a major sensitizer. The chloro derivitive is when left on the skin and used at levels higher than about 15 ppm.

    Michael just lumps everything together is incorrect. Because the chloro is sold with the non-chloro versionat a 3 to 1 ratio, he assumes boith are the cause. As the pure chloro is not a commercial product, the test kist use the mixture. The pure methylisothiazolinone is a commercial product and is recommended for leave on applications. It needs a anti-fungal agent with it to give complete protection.

  • Michael 04/23/2010, 2:29 am

    Concerning isothiazolinones; it is a wellknown fact that isothiazolinone can cause sensitization. methylchloroisthiazolinone/methylisothiazolinone (in a 3:1 combination) has been part of a standard series which tests for contact allergy in more than 20 years, it is one the most frequent sensitizing preservatives. If you search scientific databases you will find numerous studies that describes sensitization and contact allergy to isothiazolinone.

    PS. Drowning is not caused by high level of exposure to water. Drowning is caused by increased CO2 levels in the blood that forces one to inhale water.

  • Perry 06/12/2009, 3:36 am

    Thanks for the clarifications David.

    Here’s another link to the work related to the bacteria found growing in hairspray. It is not on the hair but in the concentrate. I have no idea how it survived the alcohol exposure. http://www.biomedexperts.com/Abstract.bme/18319473/Microbacterium_hatanonis_sp_nov__isolated_as_a_contaminant_of_hairspray

  • Jonathan 06/10/2009, 6:36 pm

    Also i’ve been reading about Hyaluronic Acid, dr Loren Pickart wrote something about it ,stating that it isn’t good as an ingredient ?

    1. HA sucks water out of the air and becomes wet. If you put dry HA on a dish, in about 30 minutes you would have a puddle of water. It is a very hygroscopic material, one which attracts moisture from the atmosphere. If not protected from contact with the atmosphere (by being stored under vacuum or under a dry gas) some hygroscopic materials will eventually attract so much water that they will form solutions.

    2. Then this water wets or hydrates the outer skin proteins. This weakens the proteins and loosens the protective skin barrier.

    The weak skin barrier allows bacteria, viruses, and allergens to pass through the skin. Often famous young actors in their late 20s have a very spotted skin (you often see this on a large screen) from skin barrier damage from heavy use of make up and make up removers.

    3. The wet proteins slow keratin production. The signal for the skin to send up new keratinocytes to the surface is a dryness in the proteins in the top of the skin. So skin is replaced slower and damage accumulates.

    4. Many years ago, women used Cold Creams to keep their faces moist when they went to bed. If you have seen “I Love Lucy” or old movies, you have seem women with these white creams all over their face. But they ended up with horrible wrinkles as time went by because their skin had been keep too wet.

    5. There is the idea of a limited cell life but many cell biologists doubt if this is correct. Many cells line that die in about 40 generations will live very long – such a 200 generations – as normal diploid, cancer-free cells if they are given supplemental growth factors such a fibroblast growth factor, GHK, and other hormones. No one knows how long cells can live because very long cell culture experiments are very expensive.

    The body also makes stem cells – even in adults – that can keep setting up new cell lines.”

    So is HA good or not for the skin? :(

  • Jonathan 06/10/2009, 5:28 pm

    what about airless packaging? will it be better in preserving a product?

    • Perry 06/10/2009, 6:14 pm

      Technically, airless can inhibit microbial growth. But that would require near sterile manufacturing conditions and the consumer can’t touch the product in the package. Even in an airless system it would be better to have some type of preservative.

  • David Steinberg 06/09/2009, 11:49 am

    Yeast almost never grow in cosmetics as the water activity for yeast is very narrow and is rarely obtained in any cosmetic formulation.

    Parabens also show weak activity against some Gram negative bacteria. They only function when dissolved in water. Exceeding the water solubility is a waste of money.

    Formaldehyde donors rarely dissociate in water. What causes the release is the breaking of the Nitrogen to Carbon bond: -N-CH2-OH.They are weakest aginst molds. Gulteraldehyde does not breakdown to formaldehyde. It is a very strong skin senistizer and is almost never used in cosmetics due to this and is bad odor.

    Quats function best above a pH of 7. Most are very more at any pH against pseudomonas.

    Ther is a debate if propylene glycol is really anti-microbial or is it due to its lowering of water activity. Either way the levels that show inhibition are much higher than those used in cosmetics as above 10% it causes a “burning” feeling to skin.

    Methyliosthaizoline is very weak against mold, the chloro is strongly anti-fungal. The mixture is not recommednded for leave on products.

    Chloroacetamide has been found to be unsafe by the CIR. It causes chloroacne.
    Zinc prithione do not kill bacteria they are strongly anti-fungal and yeast. The gunig cause dandruff- not bacteria.

    As to the hairspray, I have these questions-did the bateria grow in the hair or in the actual spray? How much alcohol was in the hairspray?

  • David Steinberg 06/07/2009, 4:05 pm

    Some of this information is incorrect. See the book Preservatives for Cosmetics.

    I also do not believe the article of a abacteria growing in hairspray. If the hairspray has over 20% alcohol, nothing will grow in it.

    • Perry 06/09/2009, 3:07 am

      Hello David! Thanks so much for commenting. For those who may not know, David is one of the true experts in this industry.

      The information about preservatives in this article is meant as an introduction. I’m curious which parts you believe are in error.

      I agree that it seems unlikely, but the research about the microbes in hairspray was published in the March 08 issue of the International Journal of Systematic and Evolutionary Microbiology. Perhaps they’re missing some crucial detail.

      Thanks again for your comments.

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