PRESERVATIVE SYSTEM OF COSMETICS: A Review

About Authors:
Birajdar Shivprasad M.*, Mule Madhav¹
*Department of Quality Assurance, Maharashtra College of Pharmacy, Nilanga.
¹School of Pharmacy, Swami Ramanand Teerth Marathwada University
Vishnupuri, Nanded-431606, Maharashtra, India,
*birajdar100@gmail.com

Abstract
Preservatives have been used and known to mankind since a very long time. These are used in cosmetics to increase the shelf life of product so that aroma, taste and the cosmetics itself can be stored for a longer period of time. Also cosmetics degradation is prevented by them. Preservatives, whether natural or artificial, work as in three different ways: Antimicrobial, Antioxidants and Act on enzymes. In antimicrobial, the growth of microbes like bacteria and fungi is inhibited. In antioxidants the process of oxidation is either delayed or stopped. And the one that acts on enzymes stops the ripening or aging of cosmetics product. Preservation is important part in many industries, such as the cosmetic and pharmaceutical industries, as the shelf life of many cosmetic and pharmaceutical products is important. The present review is an extensive compilation of various preservatives obtained from plant, synthetic and microbial source.The safety of preservatives is always coming into question. Since these are all biologically active products, they all have potential for being toxic, or irritating, or sensitizing.

Reference Id: PHARMATUTOR-ART-1451

Introduction¹
Preservatives are ingredients which prevent or retard microbial gram-positive, gramnegative and fungi-[yeast & mold] growth; thus protecting cosmetic products from spoilage. Cosmetic product ingredients may support the growth of microorganisms, therefore a system must be used to prevent this possibility. The use of preservatives is required to prevent product damage caused by bacteria and to protect the product from inadvertent contamination by the consumer during use. If you don’t have a preservative in the product to retard microbial contamination, you run the risk of early spoilage of the product and in the worst case scenarios, possible bacterial infections that may result in blindness. The topic of preservatives is always key to formulators and finished-goods marketers. They know they need to adequately preserve their products to ensure product safety. Formulating with preservatives is made more difficult with the industry demand that preservatives be “universally” acceptable, i.e. permitted in Japan, or that they have no connection to formaldehyde, making them acceptable in Germany. There is also the desire for the replacement of paraben or formaldehyde systems that will still cover all the requirements that are effective at low use levels, tasteless, odorless, colorless and effective against all possible microorganism contamination. There are five different preserving systems being used today. The following is a brief outline of these systems.

1. Self-Preserving Technology, is found exclusively in Usana Health Science skin care line; Sensé’s Beautiful Science skin care products. The product is the preservative in this new patent pending technology. With self-preserving, all the functional ingredients of a formula as well as the manufacturing and packaging are combined to become the preservative system. This new technology means it is no longer necessary for Sensé to use problematic chemicals like the parabens that are used by other skin care products, while still providing a preservative system that is safe for the consumer.

2.Parabens (PHBA), are used as preservatives in over 13,000 cosmetic formulations. The corporations that use parabens farm out their manufacturing to many different contract manufacturers. To protect them from possible sloppy manufacturing they add large levels of parabens to their products. Concerns are being expressed by researchers that there is evidence of parabens as estrogenic and disruptive of normal hormone function. British researchers have found traces of parabens in tissue taken from women with breast cancer. While there is no evidence that parabens cause cancer, the scientists have called for the use of parabens to be reviewed, and for more comprehensive studies to explore this possibility.

3. Formaldehyde is a colorless gas obtained by the oxidation of methyl alcohol. Vapors are intensely irritating to mucous membranes. Formaldehyde is widely used in cosmetics as a disinfectant, germicide, fungicide and preservative. Some surfactants may contain formaldehyde as a preservative without listing it on the label. Formaldehyde is an inexpensive preservative, but there are serious questions about its safety. Researchers from the Division of Cancer Cause and Prevention of the National Cancer Institute recommended in April 1983 that, since formaldehyde is involved in DNA damage and inhibits its repair it should be further investigated. Its use in cosmetics is banned in Japan and Sweden. Some cosmetic producers that advertise they do not use parabens in their products have been known to use formaldehyde as their chosen preservative.

4. Alcohol and Volatile oils, are used by companies that advertise they do not use any chemical or formaldehyde preservatives. They depend on the anti-bacterial properties of some essential oils such as tea tree oil, grapefruit seed oil and alcohol to preserve their products. These have limited use and at times their effectiveness as a preservative or an antimicrobial agent is questionable. Other problems with this system is after a substance is extracted from a plant, preserved, and mixed with other “natural” ingredients it is no longer identical to the plant it once came from. Also some of these natural oils have been preserved with formaldehyde or parabens before they are sold. The other concern is the ability of this process to fully cover all microorganisms. Many kinds of yeasts, fungi, and bacteria have been identified in cosmetics. In many instances a product might show no visible evidence of microbial contamination and yet contain actively growing potentially harmful germs.²

5. Using no preservative system, is the choice of a small number of skin care manufactures to honor their product as 100% free of any preservative, and as all natural products. These products are made in very small batches and sold in very small containers. They must be kept in your refrigerator. We are very much aware that even cosmetics products that are preserved do not last long in our refrigerators, and will go moldy or bad. Besides that problem there is the human contamination problem of the daily use of dipping your fingers into the product. This is a system that would be considered an “at your own risk” situation.

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The Important Action of Preservatives on Cosmetics

The Influence of Microorganism ³
There is no doubt that all kinds of microorganisms are widely spread around us. Although we have killed successfully an amount of microorganism in cosmetics products through sterilization in the manufacturing procedure, there are some still alive more or less. After choosing suitable preservative system and packaging, cosmetic products can be preserved well. But maybe they would be re-contaminated during consumption. Some ingredients in cosmetics, such as esters, hydrocarbon and soluble polymers tend to provide not only abundant nutrition with carbon and nitrogen sources that are necessary for microbes to grow but also chemical energy with its adduction. The microorganisms in cosmetics would grow, reproduce, and even cause the products to be spoiled once they live under appropriate conditions. The following cosmetic deteriorations are caused by microorganisms, opacities, deposition and color change by decomposing the substance; changing the product’s pH value through the catastate and the appearance through the gases created. The microorganisms may even secrete toxins, which can cause harm and skin anaphylaxis.

The microorganisms that exist in used or unused cosmetics normally include bacteria (either gram positive or gram negative), mold, and yeast. Some microbes are harmless, but some, such as Staphylococcus aureus, Pseudomonas aeruginosa, are greatly harmful to human beings.

At present, there are still not universal criteria for microbiological evaluation of drugs and cosmetics. In general, there are strict standards for baby care and eye care products. In China, according to cosmetics health standard requirement, the colonies of bacteria in cosmetics should not be more than 1000 cfu/mL (g), the colonies in baby care or mucosa products should not be more than 500 cfu/mL (g), the colonies of mold and yeast should not be more than 10 cfu/mL (g), harmful microbes such as Escherichia coli, Pseudomonas aeruginosa and staphylococcus aureus and so on should not be detected.

The Mechanism of Action of Preservative ³
A preservative actually is a protective agent to keep cosmetics unspoiled through killing or inhibiting microorganisms in cosmetic products. It doesn’t show strong instant killing effect until the preservative contacted the microbes’ cells directly at enough concentration.

Some preservatives can destroy the cleavage of cells to inhibit the microbes grow by acting on the target nucleus of microbes, such as cell membranes, cell wall, enzymes of cell. Actually, it affected the activity of enzymes or the structure of heredity particles in bioplasm. For example, the acting target nucleus of phenoxy ethanol or alcohol was cell membrane, Bronopol (2-Bromo-2-nitropropane-1, 3-diol) acted on the SH enzymes, the preservative with formaldehyde donator, such as Everguard^TM series, acted on the COOH and NH₂ enzymes in the cells, and that, the phenols and aldehydes could cause the protein denaturation. In short, the preservatives interfere cells growth through inhibiting synthesis of enzymes, proteins and nucleic acids.

Factors of Influencing Activity of Preservatives⁴
The preservatives’ efficacy depends on many factors. The preservative may be highly effective in a special system but it may be of no efficacy in others. Many factors can cause the preservative inactivation in a formula. The following are several major factors that affect preservatives’ efficacy.

Influence of pH
The pH of the system can affect the preservative’s activity through influencing the dissociation of organic acid. For example, Bronopol (2-Bromo-2-nitropropane-1, 3-diol) is very stable when its pH is 4; it also could keep active for a year when its pH is 6; but its activity only lasts several months when its pH is 7.

Influence of Particles and Gels
Some particles like Kaolin or Magnesium Aluminum silicate in cosmetics could reduce the preservative activity because of its adsorption of preservatives. However, the particles could sometimes strengthen the bacteriostatic effects through adsorbing the microbes as well.

The preservatives’ performance may be affected by combination with water-soluble high molecular weight polymer, which can bring down the concentration of free preservatives in the formulation.

Influence of Nonionic Surfactant
All kinds of surfactants in cosmetics, especially the nonionic surfactants, can interfere the activity of preservatives by solubilization and complexation. The oil soluble nonionic surfactant (HLB value is 3-6) has more de-active effect to preservatives than the water soluble one with higher HLB value. The preservative’s activity decreases with its free concentration reduction. So, the use level of preservative should be increased in the nonionic surfactants system in order to keep the same preservation power.

Influence of Preservative Decomposition
Some factors may reduce the preservation efficacy through the preservatives’ decomposition. For example, light or heat cause preservative decomposition; chemical reaction may lead to preservation inactivation or radiation sterilization may reduce preservatives’ activity.

Other Influencing Factors
In addition, there are many other factors, such as preservative distribution in oil/water phase, packaging, fragrance, chelating agents, may all interfere with preservative activity.

Ideal Preservatives⁵
No single preservative can provide a broad-spectrum anti-microbial activity at very low use levels. But, it is important for us to assume “ideal” preservative criteria so that we can develop a broad –spectrum preservative system successfully. We think an excellent preservative should at least have the following characteristics:
1) It should have broad-spectrum anti-microbial activity against both bacteria and fungi.
2) It should have excellent anti-microbial activity at low levels in cosmetic products.
3) It should be effective over a wide pH range.
4) It should be safe, non-toxic and non-irritating.
5) It should be inert, non-reactive with other ingredients in formula or container materials.
6) It should have suitable distribution coefficient of oil-water phase in order to get effective concentration in water phase.
7) It should be compatible with essentially all cosmetic materials and not to affect the color and fragrance in the finished products.
8) It should be cost effective and easy to obtain.

It is the trend that several preservatives are obtained to form an effective, broad-spectrum mixture system. An effective, broad-spectrum antisepsis performance also depends on the final formula. How to make a preservative system resist microorganisms successfully? The first thing is to avoid being contaminated in manufacturing process; on the other hand, we should avoid contamination in packaging and use procedure.

Preservative Efficacy Test Methods⁶
There are several different preservative efficacy test methods of evaluating the preservative performance in different countries, including USP method, BP method and EP method. In 1995, BP method was revised in accordance with EP method. The CTFA method is the internal method for Cosmetic, toiletries and fragrance Association in USA. Besides standard USP method and CTFA method, there are some rapid evaluation techniques, such as linear regression method, presumptive challenge test and accelerated preservation test methods. The test process of above three methods are almost the same, but there were some differences in the time needed for analysis and performance criteria. These differences could lead to different results and whether a sample passes the challenge test. So, the three evaluation methods of USP, CTFA and Linear Regression methods are discussed below, and selection of microorganisms, inoculums level, measuring intervals and acceptance criteria are compared. Table 1 gives the details for these three methods.

Table1 The Comparison of Three Evaluation Methods

Discussion of Preservative Efficacy Test Methods ^7,8
How to choose microorganism in challenge test
From the above, we can find that the same microorganisms in the challenge test can be adopted in the three evaluation methods of USP, CTFA and Linear Regression: staphylococcus aureus, Pseudomonas aeruginosa and Aspergillus niger. The test procedure shows the organisms changes during the products manufacture and consumption. Although these recommended strains are representative, the seudomonas cepacia is recommended mightily to get the broad-spectrum preservative system. Seudomonas cepacia is a non-fluorescent monad, such as Pseudomonas aeruginosa, which is more sensitive to preservatives than fluorescent monad. Furthermore, the organisms separated from environment or housing microbes recommended by CTFA shall be considered as well, because these microbes are more likely to be present in the products. It is the most ideal if the challenge test can be performed with both the standard trains and the separated organisms partly if the condition permits.

Rationality of Re-challenge Test ^11,12
The aim of re-challenge test is to reassess contamination during product use period. It shows the number of challenge test that the preservative system could hold before the system breads down by repeated inoculation with special microorganisms. It is un-necessary to go on re-challenge test for linear regression method, because the microorganisms’ death rate of tested formula that contained enough preservatives really has nothing to do with the amount of microorganisms during the test time.

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Acceptance Standard
Linear regression method determined (expressed by ‘D’ value) the decimal-reduction time of microorganism in challenge test, namely, the time that a 90% microorganism reduction required. This method is used by traditional microorganism measurement –APC. The evaluation speed by the linear regression method is quicker than CTFA and USP method.

The results of USP and CTFA methods indicated ‘pass’ or ‘fail’. The linear regression method result is showed by the D value that could be determined from a survivor curve by the construction method and least-squares method. The curve is prepared by plotting the number of viable organisms recovered at various times.

We could compare the test standard of microorganism death rate of USP and CTFA method with linear regression method through translating the D value. The D value for bacteria in USP method is 112; the D values for bacteria and fungi in CTFA are 56 and 168, respectively. They all are far greater than the D value 4 and 28 in linear regression method. It is clearly that the standard of linear regression method is stricter than USP and CTFA methods. It has been shown that no re-contamination of adaptation microbes have been found in products that passed the acceptance standard of linear regression method. The preservative system, if it passed the test of linear regression method, has less possibility of failure than if it only passes the test of USP or CTFA methods. It is illustrated that the linear regression method provides a more reliable means of performing preservative efficacy tests.

Experimental Time
Linear regression method is a rapid preservative evaluation method. The test of pathogens such as staphylococcus aureus and Pseudomonas aeruginosa could be compared within 3 days and the test of non-pathogens could be completed in two weeks. The test period of USP and CTFA method are both 28 days, it even needs 8 weeks if it is continued with re-challenge test. But the evaluation time is greatly shortened for linear regression method because it is unnecessary to go on for re-challenge test.

There is still not a fully standardized method by now to evaluate the preservative systems in cosmetics and personal care products. In fact, many large-scale companies have built internal criteria for evaluation according to the USP method or CTFA method. Under the same condition, it is suggested that Linear Regression method could be alternatives to evaluate the efficacy of preservative systems because it is easy, quick and reliable evaluation method.

What Makes a Good Preservative?^9,10
To overcome the broad spectrum of microbes, and at the same time, not to be harmful to the skin and deleterious to other ingredients in a cosmetic product, it is critical to use the right preservative. The optimal preservative should have the following attributes:
• Broad spectrum activity (bacteriae & fungi)
• Be effective over the anticipated shelf life
• Be preferably liquid and water soluble
• Be effective over a wide pH range
• Not be deactivated by other ingredients
• Be odorless, colourless, and safe

The following table gives an overview of the most used synthetic preservatives in the cosmetic industry. They all have been tested for efficacy and safety. By far the most used preservatives are the parabens (in about 80%).

Appropriate Use of Preservatives
Every cosmetic formulation requires a tailormade preservative system to meet its specific needs. Several factors influence the choice and dosage of a preservative:
• Working conditions (clean environment and equipment reduces amount of preservatives)
• Type of product (leave-on and eye-area products require more preservatives)
• Type of formula (some preservatives work less effectively in complex emulsions)
• Combinations (by combining preservatives the amount of each agent can be reduced)
• Length of shelf life (the longer the desired shelf life the more preservatives are needed) Based on these factors there is no standard preservative system that can be utilized for all kinds of cosmetic products. Nevertheless the following table gives some clues on how the shelf life of a cream can be prolonged:

Measures to Reduce Preservatives
Although preservative-related side-effects as skin irriations and allergies occur very rarely, use of preservatives should not be excessive (do not use them at higher concentrations than allowed by the FDA or other authorities). There are additional possibilities to avoid premature spoilage of homemade cosmetics:
• Disinfect the working utensils and containers with isopropyl alcohol or by putting them in boiling water for 20 minutes.
• Use sterilized (boiled for 20 minutes) and distilled water for your products
• Make your products in small batches only and not in family sizes that last forever
• Do not dip your fingers into your products (particularly creams). Use a spatula or
spoon
• Store your products in the refrigerator and label the product with the date of production. Keep products out of the sunlight and sunheat.

Loss of Effect of Preservatives
Besides a gray-green layer of mold on the surface of a product, there are several other factors indicating that a cosmetic product is severly contaminated with microbes:
• Loss of viscosity (product becomes thinner)
• Emulsion break (separation of water and oil)
• Cloudiness of previously clear products
• Loss or change of color or malodorousness
• Drop in pH (product becomes more acid)

In conclusion, it is strongly recommended to preserve your homemade products! Do not be afraid of using synthetic preservatives. They are truly effective and safe. But do not forget to work clean! If your product has spoiled though, throw it away. Adding preservatives will not make it usable again

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17.    Townsend Letter for Doctors and Patients, July 1, 2004.
18.    Rose Marie Williams, “Think before You Pink; Breast Cancer Awareness,” Townsend Letter for Doctors and Patients, October 1, 2005.
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23.    Critical Review of Toxicology Vol. 35, Jun 2005, pp. 435- nlm.nih.gov/pubmed/16097138.81 Ibid.

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