Preservatives: Good, Bad and Ugly

by Barbara Bird CMG

“The importance of keeping our personal care products free from microbes must not be underestimated.”

Dr. Stephen and Gina Antczak, Cosmetics Unmasked

What are microbes and why should we be concerned? The term “microbe” is used to describe any micro-organism such as molds, fungi, yeasts, bacteria and protozoa that can contaminate and infect cosmetic products. Shampoos and conditioners are especially likely to become contaminated because they are water-based solutions and water provides a highly favorable environment for microbes to multiply and thrive.(1)

Even using best manufacturing practices and de-ionized or purified water, all grooming products that contain water will contain some microbes. Preservatives are necessary to keep them from multiplying and proliferating so as to contaminate the product. Not only does microbial proliferation damage the product and possibly render it ineffective, the contaminated product can become a health hazard.

The danger is that the microbes in contaminated pet products can be transferred to the pet or bather and start an infection. The microbes may feed on body tissues, causing skin damage and infection, or may release toxins into the bloodstream, resulting in systemic illness, such as urinary tract disorder.


In this day of treatment-resistant staph and bacterial infections, there is even greater concern on the part of formulators to keep products safe from microbial contamination. From the moment a product is opened for first use it is assaulted by additional microbes. They are everywhere – in the air, on our hands, on all surfaces. Products in jars are particularly at risk for contamination because we dip our fingers into the jar, injecting zillions of bacteria.(2) When was the last time you washed your hands before bathing a dog?

As described by the Antczaks, reproducing microbes “usually produce a bad smell and may cause some clear products to become cloudy. They also release toxic substances as waste products, to help them digest and absorb food, and to kill other microbes that may be in competition with them.

They can also chemically alter ingredients, causing colors and odors to change. The altered substances may be poisonous or harmful.”(1) The lack of bad odor, color change, ingredient separation or fuzzy stuff on the surface does not guarantee that a product is free of contamination. A shampoo or conditioner can be seriously contaminated before there are visible signs.(2)

Among the dangerous contaminants that can develop in unprotected shampoos and conditioners are those that cause nasty staph infections and pseudomonas aeruginesa that cause skin and ear infections in dogs. For a really scary list of microbes found in cosmetics, take a look at the article by Perry Romanowski, “Why There Are Preservatives in Cosmetics” cited in our references below.(3)

It is the responsibility of the manufacturer of human cosmetics to sell only products that can be assuredly safe. Most products that are manufactured for commercial use contain preservatives that can assure at least a two-year shelf life. While pet products are not governed by the same regulations that cover human cosmetics, most manufacturers assume similar responsibility.

The perfect preservative? What makes a preservative ingredient or complex good or bad? From the user’s point of view it is often a matter of toxicity. The ugly truth is that all cosmetic preservatives are potentially toxic. They must be biocidal to do their job. Any substance that can kill living cells has the potential to be toxic. This includes naturally derived substances as well as synthetic chemicals. It’s the dose that makes the poison. From a formulator’s point of view, what makes a preservative good or bad is its effectiveness within safe levels of use.

There are many criteria for an ideal preservative or preservative system. The most important are:(4)

  • Broad spectrum of activity
  • Effective and safe at low concentrations
  • Cost effectiveness
  • Does not negatively interact with any other ingredients or become inactivated by other ingredients.
  • Water soluble and oil insoluble
  • Stable under all temperatures and pH conditions that would occur during manufacture and use.
  • Colorless and odorless.

In order to be effective against all the possible microbes that can enter a shampoo or conditioner system, preservatives need to be very broad spectrum and offer protection from mold, fungi, and both Gram-positive and Gram-negative bacteria.

Almost all single preservatives have some area of weakness or coverage “gap.” For example, the parabens are not very effective against some bacteria, such as Pseudonomas, a Gram-negative bacteria. Phenoxyethanol, a very popular alternative to Parabens has poor effectiveness against mold and fungi. Every preservative has its strengths and shortcomings. For this reason combinations are often used.(4)

Many of the major chemical suppliers now offer preservative “systems” which are premixed blends of preservative ingredients. These blends have been carefully developed by chemists to achieve optimum efficacy with the lowest possible concentrations. Although it may appear on the label to look like there are more preservatives, the overall total percentage of preservative ingredients using a blend might be the same or less than formulating with just one or two.

Preservative combinations also have the ability to act synergistically, allowing for less of any one substance. Tetrasodium EDTA, for example, boosts the preservative activity against mold and fungi by binding the mineral ions in a water solution. EDTA also softens the water, making the cleaning agent more effective.(5)

What about natural preservatives and preservative-free formulas? Good question. Chemical suppliers are scrambling to meet the demand for friendlier appearing preservatives or ingredients that will preserve cosmetic preparations while not looking like nasty chemicals on the label. There is a lot of work being done, but finding substances that meet all of the criteria listed above is a daunting challenge.

Natural preservatives often have to be used in ten times the concentration of the traditional chemicals, and that can wreak havoc with the balanced blend of the other ingredients, as well as cause color and odor issues in a formula. Natural preservatives are also formulation specific and batch specific; what works in one formula may be ineffective in the next, and what works in one batch may not work in the next. This is due to the natural variations in the composition of truly natural substances. Also, as cosmetics are becoming more and more loaded with botanical extracts and protein ingredients, preservation becomes more challenged.

Microbes feed on plants and proteins. Because it can take years to test and prove the efficacy and safety of new preservatives, it may be awhile before mainstream manufacturers and their formulators give up the tried and true values of the traditional chemicals. We must keep in mind that a substance that is “natural” is not necessarily safer or somehow better than a substance that is created in a lab.(4)

Regarding “preservative-free”: don’t believe it unless the product requires refrigeration. Shampoos and conditioners that claim, suggest or imply that there are no preservatives are either not telling the truth or are using preservatives that can be camouflaged as having a function other than preservation. Phenoxyethanol is such an ingredient; it can be labeled as “fragrance.”(4) Because of the public’s fear of chemicals fueled by sensationalist journalism and fear mongering, pet product manufacturers sometimes opt to simply not disclose their preservatives. This is not illegal.

You can’t blame companies for wanted to hide information, as more and more groomers are becoming Internet educated ingredient police.

Common Myths and Misunderstandings: Never has a fear campaign against a cosmetic ingredient sparked such a wildfire of fear and condemnation as what has happened to paraben preservatives.

Parabens were the most widely used preservatives for at least four decades before a small study of 20 individuals in 2004 discovered some paraben metabolites (not even parabens themselves) in breast cancer tissue samples.

The study itself did not draw a connection between the use of parabens and the cancer, but the media did. The firestorm began and raged over the Internet. The misunderstanding of the science was repeated so loudly and so often that many folks today believe it is common knowledge that parabens cause cancer. False! An extensive range of global studies has shown that parabens are metabolized and excreted by the body. Nor do they exert significant estrogenic activity, another misunderstanding and false assertion. It has been clearly shown that the estrogenic activity of parabens is 10,000 times less than that of naturally occurring phytoestrogens and medicines that we consume daily. Paula Begoun, the “Cosmetics Cop” sums it up thusly: “The truth is that on a global scale, there is an exhaustive degree of scientific and medical studies demonstrating the safety of parabens used in skin care and cosmetics.

So the next time you read a story that vaguely indicates parabens are unsafe, think twice before you believe the hype and remember the facts–the tiny levels used in your personal care products are not harmful.”(7) Not only are they not harmful as used in grooming products, but also did you know that parabens are naturally occurring chemicals? Now you do!(7)

Another use of fear and scare tactics for negative marketing has been the misinformation about the group of preservatives that release formaldehyde. Formaldehyde donors include DMDM hydantoin, diazolidinyl urea, imidiazolidinyl urea, and quaternium 15.

Formaldehyde gas is an established carcinogen. Advocacy groups loudly proclaim this and demand that manufactures remove this cancer-causing ingredient from cosmetics. Websites and newsletters wave this flag of fear to show that they care about people while the cosmetics industry clearly does not. The truth?

Formaldehyde gas is not nor ever was a cosmetic ingredient. Formaldehyde is a gas neither a liquid nor a solid. It does not dissolve in water.  When formaldehyde gas is exposed to water, it immediately becomes another substance, methylene glycol.(8) Moreover, formaldehyde is another naturally occurring substance. It is found in many fruits and vegetables, including apples, pears, onions and cauliflower. The amount of formaldehyde released by these preservatives is at least 100 times less than found naturally in foods.(9)

Another bit of misinformation that has been allowed to go unchecked is the belief that cosmetic ingredients penetrate the skin and enter the bloodstream. This myth fuels the distrust of many cosmetic ingredients, including preservatives. The truth is that the skin is a barrier, not a sieve, and very little penetrates the stratum corneum and even less reaches the inner layers. This is especially true of rinse off products such as shampoos and most conditioners.(10)

One result of these scare tactics and the dissemination of misinformation is that pressure builds on formulators to abandon some tried and true options for safe preservation.

It takes years for the safety of new preservatives to become established. No cosmetic ingredient has been as exhaustively studied as parabens. Countless mice, rats, guinea pigs have been sacrificed to prove the safety of these substances, and although the safety has been established for the dosages as used in cosmetics, parabens are being forced out of the formulators’ tool box by misinformed public opinion.

Less well-established preservatives are taking their place or substances that do not meet as many of the criteria for a chemically “good” preservative. Think about it!

A valid concern: While preservatives in cosmetics, especially shampoos and conditioners, are not the cancer causing endocrine disruptors they have been blown up to be, there is one important truth to be noted. Next to fragrances, preservatives are the ingredients most likely to cause contact dermatitis and allergic reactions in sensitive individuals. This is the real reason we need to urge pet grooming product manufacturers to inform us of the preservatives they are using.

Unfortunately, some of the preservatives that have been used as substitutes for parabens are significantly more likely to be sensitizers. Parabens are among the least likely to cause allergic reactions. Methylchloroisothiazolinone and Methylisothiazolinone (MCI/MI) is a preservative that had a big surge in use as formulators started replacing parabens that has turned out to be a serious sensitizer. Some of the formaldehyde releasers are also troublesome sensitizers. Of this group, DMDM Hydantoin has shown the least allergic reactions in humans, and Quarternium-15 the worst.

Allergic reactions to grooming products are a tricky problem for groomers and our clients alike. First of all, sensitization occurs over time; it can be caused by a product that the groomer has previously used on that dog without a noticeable problem. Secondly, an allergic reaction may be slow to manifest; it may not show up at the grooming salon. It can take as long as a day or two to become full blown. This makes for a difficult customer relations scenario. Likewise, an infection or problem caused by a contaminated product also can take days to develop.

It is important for all professional groomers to recognize the reality that grooming products can trigger problems that show up later at home. Just because the dog looked fine after your grooming does not mean that a problem is not related to the grooming.

One serious possibility is in the use of diluted products. Most commercial pet shampoos are intended for dilution before use. The amount of preservatives in pet shampoo is appropriate for the concentrated product; it does not extend to the diluted shampoo.

Products diluted with tap water are especially at risk, as you are infusing them with a fertile crop of microbes. These diluted products should be used in a day or two and then tossed or refrigerated. Using distilled water will give you more safe time, but any diluted product is virtually unprotected from microbe proliferation.

Old unused products are also at risk, especially those that have been opened and partially used. Microbes are airborne as well as carried by water. Every time a bottle or jar is opened it is exposed to potential contaminants. Bathing rooms are warm, moist environments – a fertile garden for microbe proliferation. Vans and grooming trailers are even more supportive of microbial growth, as they are subject to more extreme temperatures and humidity. The same conditions that make for rusty blades put your products at risk as well.

The bottom line? It would seem that a bottle of shampoo is more likely to suffer contamination than to cause cancer. In regards to negative marketing, Franklin D. Roosevelt’s words seem to apply, “The only thing we have to fear is fear itself.”  ♦


(1.) Cosmetics Unmasked, Dr. Stephen Antczak & Gina Antczak, Thorsons, London, 2001, pgs. 31-38.

(2) Why Cosmetics Need Preservatives, Kayla Fioravanti, Personal Care Truth or Scare, June 2, 2010.

(3) Why There Are Preservatives in Cosmetics, Perry Romanowski, The Chemists Corner, February 9, 2012.

(4) Preservatives for Cosmetics, David C. Steinberg, Third Edition, 2012, Allured Books.

(5) A Closer Look at EDTA, Kayla Fioravanti, Personal Care Truth, June 16, 2010,

(6) Understanding the Need for Preservation in Personal Care, Laura M. Szymczak-Frye, Global Marketing Manager, Personal Care Preservation, Lonza

(7) Parabens: Are They Really a Problem? Paula Begoun,

(8) Exposing the Formaldehyde Myth, Doug Schoon, Personal Care Truth, August 11, 2010.

(9) Foods Known to Contain Naturally Occurring Formaldehyde, PDF,

(10) The Impermeable Facts of Skin Penetration and Absorption, Nathan Rivas, Personal Care Truth, January 18, 2011.


How to Prevent Contamination in Cosmetic Products, Perry Romanowski, The Chemists Corner, April 5, 2014.  – An excellent overview of preservatives used in human cosmetics.

Facts about DMDM Hydantoin, Barbara Bird, BBirdTalk, November 29, 2013, – a more complete discussion of the misinformation about formaldehyde donor preservatives.

Why We Don’t Use Neem Oil as a Preservative, Norman L. Polston and Grace Bezanson, Ezine Articles, March 29, 2013, – an interesting example of the complexities of using natural preservatives.

Effects of Biocides on Antibiotic Resistance, – Are preservatives hurting us in the long run?