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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

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.


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 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.


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.


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. 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.

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{ 8 comments… read them below  }

1 David Steinberg 06/07/2009 at 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.


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2 Perry 06/09/2009 at 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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3 David Steinberg 06/09/2009 at 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?

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4 Jonathan 06/10/2009 at 5:28 pm
what about airless packaging? will it be better in preserving a product?

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5 Perry 06/10/2009 at 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.

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6 Jonathan 06/10/2009 at 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?


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7 Perry 06/12/2009 at 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.

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8 Michael 04/23/2010 at 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.