Preservatives play a vital role in product formulation. For the purpose of this review, personal care including cosmetics is defined as a chemical product having intended end uses primarily on the human body (products not intended for ingestion, with the exception of food supplements). In general, these products are designed to alter odor, appearance, touch or taste without displaying significant biochemical activity. Microbial contamination in cosmetics, toiletries and personal care products is very common and has been of great concern to the industry for many years. Bacteria, yeast or fungus all cause microbial spoilage. All of these are extremely diverse in their metabolic activities. The metabolic reactions of microorganisms can cause health hazards because of the degradation of the product that can be toxic, mutagenic and so on.1
Several microorganisms produce toxic waste products and render a product unfit and dangerous if they grow under conditions that support toxin production. Endotoxin, produced by gram-negative bacteria, is not necessarily deactivated by sterilization, because it is heat stable. In order to pick an appropriate preservative system for a cosmetic product, the chemist must be familiar with the composition, morphology, ecology and diversity of microorganisms and their influences on our daily life. This knowledge enables the chemist to interpret the mechanism of action of the organism involved and effectively deal with consequential contamination.
A bacterium is structurally the simplest and most abundant of organisms and can live in soil, water, organic matter or in plants and animals themselves. Bacteria are significant to man because of their chemical effects and the role they play in the spread of disease. In fact, life on earth would not exist without bacteria, which make possible many of the essential functions of ecosystems. A bacterium of typical size is about 1-2 microns long, making it completely invisible to the naked eye. Bacteria belong to the prokaryote class because their nuclear region is not surrounded by a membrane and consists of a single DNA molecule whose division is non-mitotic.
In contrast, algae, fungi and protozoa are eucaryotes, as their nuclei are bound by a nuclear membrane, contain several DNA molecules and undergo division by the well-known process of mitosis. The algae refer to a large and diverse assemblage of eucaryotic organisms that contain chlorophyll and carry out oxygenic photosynthesis. The fungi, which lack chlorophyll, are a large and diverse group of eucaryotic microorganisms. There are three groups of fungi, having major practical importance: molds, yeasts, and mushrooms. The habitats of fungi are quite different from each other. Some are aquatic, living primarily in fresh water, though a few marine fungi have been identified. Most fungi, however, have terrestrial habitats, in soil or on dead plant matter, and these types often play crucial roles in the mineralization of organic carbon in nature. A large number of fungi are parasites of terrestrial plants. Indeed, fungi cause the majority of economically significant diseases of crop plants. A few fungi are parasitic on animals, including humans, although in general fungi are less significant as animal pathogens than are bacteria and viruses.
Infectious diseases caused by fungi are called mycosis, and three kinds have been recognized: superficial, involving only the skin; subcutaneous, in which fungal growth occurs beneath the skin’s surface and systemic, which involves fungal growth in internal organs of the body. It has been estimated that only about 50 species cause human disease and many mycoses are due to infections caused by opportunistic fungi, which ordinarily are harmless. Therefore, the cosmetic chemist should not ignore their serious infectious threat while selecting a preservative that also covers fungus. Nail and skin infections are common among swimmers and beach goers, while bacteria are often maligned as the causes of human and animal diseases. A classic example is pseudomonas aeruginosa, a bacillus commonly found on human skin. While generally innocuous, it is dangerous when a person’s immune system is compromised, especially in patients with severe and widespread burns.
However, certain bacteria, including actinomycetes, produce antibiotics such as streptomycin. Similarly bacteria are immensely important because they convert nitrogen into a usable form on certain plant roots or provide the tang in yogurt. Bacteria are used in the production of acetic acid and vinegar, various amino acids and enzymes, and especially in the fermentation of lactose into lactic acid, which coagulates milk proteins and is used in the production of nearly all cheeses, yogurt and similar products. They also aid in the breakdown of dead organic matter. Today, genetic engineering methods are used to improve strains of bacteria for commercial use and hold enormous promise for the future. In cosmetics, many of the actives, such as low molecular weight proteins and peptides, anti-wrinkle ingredients and antioxidants, are being created with the use of improved specific bacterial strains.
Most bacteria may be placed into one of three groups based on their response to gaseous oxygen. Aerobic bacteria thrive in the presence of oxygen and require it for their continued growth and existence. Other bacteria are anaerobic, and cannot tolerate gaseous oxygen. The third group is the facultative anaerobes, which prefer growing in the presence of oxygen, but can grow without it. Bacteria are rod-shaped (bacilli), spherical (cocci) or spiral (spirilla) in form. Bacilli or cocci may adhere in small groups or chains.
A typical bacterium has a cell membrane surrounded by a cell wall. The lone exception to this is the mollicutes group, which includes pathogens such as the mycoplasms. The composition of the cell wall varies among species and is another important characteristic for identifying and classifying bacteria. Gram-positive bacteria have a fairly thick cell wall composed of peptidoglycan (carbohydrate polymers cross-linked by proteins) and retain a purple color when stained with a dye known as crystal violet. Gram-negative bacteria have double cell walls, consisting of a thinner wall of peptidoglycan and an outer wall of carbohydrates, proteins and lipids. They do not stain purple with crystal violet.
The most important difference between gram-positive and gram-negative organisms is the latter’s additional lipopolysaccharide and protein layer. The lipopolysaccharide layer makes gram-negative bacteria more resistant to the effects of preservatives than gram-positive bacteria. Therefore, it is not only the chemical constituents that determine susceptibility to lipophilic preservatives, but also the physical structure of the wall. In fact, the effect of preservative agents on a bacterial cell varies according to the microorganisms used. In this regard, yeast and fungi have also been found in gram-positive organisms. The cell walls of yeast and fungi are composed of two or more protein polysaccharide complexes held together by a variety of covalent bonds. The presence of mannan as a cell wall component distinguishes yeasts from other fungi.2
When healthy, internal tissues, blood, brain and muscle are normally free of harmful microorganisms. On the other hand, the surface tissue, skin and mucous membranes are constantly in contact with environmental organisms. Literally billions of bacterial cells are present in and on the human body and most play beneficial, indeed sometimes even essential, roles in the overall health of the person. These organisms are collectively referred to as the “normal” flora, and represent species that have developed an intimate relationship with certain tissues of the human body. This balance is extremely complex and consists of more than 200 species of bacteria. Many of the normal flora are either pathogens or opportunistic pathogens.
A Look at Skin
The skin, along with the respiratory tract, gastrointestinal tract and other body regions, provides a wide variety of chemical and physical conditions in which different microorganisms can grow selectively. Further, skin possesses a variety of defense mechanisms that act in concert to prevent or inhibit microbial invasion and growth. The microorganisms that have developed ways of circumventing these defense mechanisms ultimately colonize successfully. The majority of skin microorganisms are found in the most superficial layers of the epidermis and the upper parts of hair follicles. Most skin microorganisms are also associated directly or indirectly with the sweat glands, which are rather unevenly distributed over the body, with denser concentrations on the palms, finger pads and soles of the feet. They are the main glands responsible for the perspiration associated with cooling of the body.
Eccrine glands seem to be relatively devoid of microorganisms, perhaps because of the extensive flow of fluid, since when the flow of an eccrine gland is blocked, bacterial invasion and multiplication occur. The apocrine glands are more restricted in their distribution, being confined mainly to the underarm regions. Bacterial populations on the surface of the skin in these warm, humid places are relatively high, in contrast to the situation on the smooth surface of the skin. Underarm odor develops as a result of bacterial activity on the secretions of the apocrines; aseptically collected, apocrine secretion is odorless but develops odor upon inoculation with certain bacteria isolated from the skin.
Each hair follicle is associated with a sebaceous gland, which secretes a lubricant fluid. Hair follicles provide an attractive habitat for microorganisms. A variety of aerobic and anaerobic bacteria, yeasts and filamentous fungi inhabit these regions, mostly within the area just below the surface of the skin. The secretions of the skin glands are rich in microbial nutrients. Urea, amino acids, salts, lactic acid and lipids are present in considerable amounts. The pH of human secretions is always acidic, between 4 and 6.
The microorganisms of the normal flora of the skin can be classified as either transients or residents. The skin as an external organ is continually being inoculated with transient bacteria, virtually all of which are unable to multiply and usually die. Residents are organisms that are able to multiply, not merely survive, on the skin. The normal flora of the skin consists primarily of gram-positive bacteria restricted to a few groups. These include several species of staphylococcus and a variety of both aerobic and anaerobic corynebacteria. Of the latter, propionibactrium acnes is ordinarily a harmless resident but can incite or contribute to the condition known as acne. Gram-negative bacteria are almost always minor constituents of the normal flora, even though such intestinal organisms as escherichia coli are being continually inoculated onto the surface of the skin by fecal contamination. Acinetobacter is the only other gram-negative bacterium commonly found on the skin. It is thought that the lack of success of gram-negative bacteria is due to their inability to compete with gram-positive organisms that are better adapted to the skin. If the latter are eliminated by antibiotic treatment, the gram-negative bacteria can flourish. They consist largely of micrococci (staphylococcus epidermis and micrococcus sp.) and corynebacteria. Most bacterial infections of the skin can be accounted for by three pathogens, staphylococcus aureus, streptococcus and pseudomonas.
Yeasts are uncommon on the skin surface, but the lipophilic yeast pityrosporum is occasionally found on the scalp.
Although the resident microflora remains more or less constant, various factors such as weather, with an increase of temperature and humidity, increases the density of the skin micro- flora. Young children have a more varied microflora and carry more gram-negative bacteria and potential pathogens than adults. Similarly, hospitalized patients have greater numbers of pathogens and antibiotic-resistant organisms than healthy people. Personal hygienic habits influence the resident microflora and unclean individuals usually have higher population densities. Organisms introduced on to the skin that subsequently die, generally succumb from either the skin’s low moisture content or low pH. Organisms that survive and grow are able to resist these adverse chemical conditions. The most common contaminants in a cosmetic product include bacteria such as staphylococci, pseudomonas and other opportunistic bacteria. The corynebacteria, and certain related propionic acid bacteria, are consistent skin flora and some of them have been implicated as a cause of acne.3
The Use of Preservatives
In order to protect the cosmetic product from decay, discoloration or spoilage, we use preservatives. A preservative is a material that protects the product from the effects of microbiological contamination. The selection of a germicidal is critical and in many cases chemicals, which are highly active against microbes, also have similar effects against mammalian cells. Therefore, a balance needs to be established with the preservative of choice between killing organisms which may attack the cosmetic product and injure the cells of the consumer who use the product.
Over the years, the list of preservatives has grown continuously and concerns regarding safety and skin’s sensitization have become a big issue. Today’s cosmetics are complex and need to be preserved with efficient, safe microbial agents that perform continuously. To find the right type that fulfills all criteria such as safety and freedom from sensitivity and irritation to the skin has become quite a job. The ideal preservative system should carry the following parameters:
1. It should have a broad-spectrum antimicrobial activity against both gram-positive and gram-negative bacteria including fungi.
2. It should be effective over a wide pH range and remain active during the shelf life of the product.
3. It should be non-toxic and non-irritating.
4. It should not react with the other ingredients in the formula and should continuously provide activity during ambient temperature or storage conditions.
5. It should not react with the packaging or container.
6. It must have a suitable oil/water partition coefficient to be available in an effective concentration in the aqueous phase of the product.
7. It should not interfere with the color or the fragrance of the finished product.
8. It should be cost-effective.
No single antimicrobial agent can possibly meet all these criteria. Therefore, a mixture of more than one chemical is required to constitute an acceptable preservative system. Among the list of preservatives, parabens are widely supported by the majority of chemists. Besides preserving the product from deterioration, the preservative system should protect the product against contamination from outside exposure, which is inflicted through frequent product usage with fingertip application. As a result, the product should pass the challenge tests employing certain procedural artifices. The preservative should also control the proliferation of microbial growth that may adversely affect the health of the consumer.
The system should be free of toxicity with minimal irritation. A great many sensitivity problems in new product formulations arise because of chemical interactions between preservatives and substances added as stabilizers or bulking excipients to improve the product’s aesthetics. In fact, many interactions of preservatives were recognized years ago. The formation of preservative complexes with materials such as ethoxylated and propoxylated emulsifiers, resins and proteins are the classic examples in which the preservative activities, especially lipophilic germicides, have been drastically curtailed. Some interaction was also detected with polyethylene glycol, methylcellulose, polyvinyl pyrrolidone and gelatin, but this was considerably less than that observed with the nonionic, e.g., Tween 80. No significant interaction was observed with carboxymethylcellulose or tragacanth.4 Sorbic acid and boric acid did not complex with glycols.5 In reality, a compound that shows marked toxicity to microorganism cells is likely to exhibit toxicity to human cells. Selecting contaminant-free ingredients for the construction of the final product and providing bacteria-free processing equipment and environment can overcome this problem. Many of the raw materials such as certain color additives, gums, proteins, talcs and other materials from natural sources may contain indigenous microorganisms at significant levels. Similarly, many of the cosmetic products can promote microorganism growth because they are biodegradable. Therefore, cleanliness and the use of contaminant-free raw materials must be enforced strictly in manufacturing operations to achieve an adequately preserved product. Traditionally, there are eight major means of microbial control:
1. Chemical preservatives.
2. Manipulation of pH.
3. Limitation of water content.
4. Use of hostile materials.
5. Addition of preservative in suitable phase; e.g. oil or water
6. Addition of preservative at an appropriate temperature.
7. Aseptic manufacturing.
8. Tamper-proof packaging.
Experience has shown that a trio of preservatives works best in cosmetic products instead of singly or in pairs. Some common cosmetic ingredients are not considered preservatives but are included in the product to create an environment hostile to the microorganism to grow in a cosmetic product. These compounds include alcohol, propylene glycol and butylene glycol. Similarly, cationic and anionic surfactants, chelating agents (EDTA), aldehydes, phenolics other than parabens, essential oils and spices are excellent ingredients to discourage microbial growth in a product. At the appropriate concentration, glycol has preservative effects. While the inhibitory concentration of the agents would make them unacceptable in most products, at lower concentrations they do affect the favorable partition of the preservative into the aqueous phase.6 A product is traditionally preserved in many ways to control the microbial growth; among them, the addition of chemical preservatives is the most widely used practice. These chemicals constitute an important component of any formula and are usually included at levels of less than 1%.
Formaldehyde has always been one of the most effective. The two most familiar names among the formaldehyde donors include imidazole urea (Germall 115) and dimethyllol-5, 5-dimethylhydantoin (DMDMH).
DMDMH is said to be the most advanced, next generation chemical preservative that produces the lowest free formaldehyde with greater safety.7
Sorbates and benzoates are very effective preservatives and due to their water solubility are equally popular in cosmetics and food products. Dehydroacetic acid is another chemical which is also frequently used as an effective cosmetic preservative. The omnipresence of parabens (esters of parahydroxybenzoic acid) make them by far the most widely-used chemical in cosmetics and personal care products, although the acute toxicity of these compounds is very low. Routledge et al. reports that these compounds (methyl through butyl homologs) display weak estrogenic activity in several assays.8 Although the risk from dermal applications in humans is unknown, butylparaben showed the most competitive binding to rats’ estrogen receptors at concentrations one to two orders of magnitude higher than that of nonylphenol and showed estrogenic activity in yeast estrogen screen at 10--6M.
Organic mercurial currently finds a limited use only in eye products unless its need is absolutely necessary due to the failure of other preservatives. Another effective way to achieve product self-preservation has been by limiting the microbial growth at the extreme pH ranges. The pH between 3-4 (acidic) and pH 9 and above has been a continuous practice to keep the product clean. However, the biggest drawback is eye and skin irritation that occurs at extreme pH. Lowering the water content to a level that does not readily support microorganism growth is another technique to keep the product clean for a longer time period. In many instances microorganisms’ growth has been restricted with the inclusion of hostile materials such as alcohols, propylene glycol, 1,3-dibutylene glycol, chelating agents (EDTA) and antioxidant sodium bisulfite.
Some of the less traditional means—freeze-drying, freezing and sterilization that create the bacteria-free environment without utilizing preservatives—can also be considered for sophisticated cosmetic products. However, these techniques, while effective, are expensive. It is also well-known that certain essential oils and fragrances have shown good preservative activity but their presence at a certain level in the product is critical and needs to be monitored.
Triclosan (Irgasan DP 300, a chlorinated biphenyl ether: 2, 4, 4’- trichloro-2’–hydroxydiphenyl ether) is another antiseptic agent that has been used for nearly 30 years in a vast array of consumer products. Its use as a preservative and disinfectant continues to grow; for example, it is incorporated at <1% in Colgate toothpaste. While triclosan is registered with the U.S. Environ- mental Protection Agency as a pesticide, it is freely available for use in over-the-counter products. Triclosan’s use in personal care products such as hand soap, acne cream, foot deodorant cream and, rather recently, as a slow-release product called Microban, is noticeable. The only concern to cosmetic chemists is reports of bacteria becoming resistant to triclosan.
Phytosphingosine is one of the newest biotech entries that is perceived to mimic the skin’s own natural phytosphingosine to inhibit the growth of harmful skin microorganisms such as P. acnes, P. aeruginosa and S. aureus.9
The concept of self-preservation and the natural preservatives is a relatively new concept in the area of cosmetics and personal care products. Tea tree oil and grapefruit seed extract are the newest entries. Grapefruit seed extract10 is claimed to be effective on a broad spectrum of bacteria, fungi and viruses. For preservation purposes, grapefruit extract is usually recommended at 0.2 and 1.0% concentrations. However, self-preservation is a naïve term mostly used for natural cosmetics. The lack of preservatives in commercial cosmetics and self-mixed preparations creates the ideal breeding ground for bacteria and fungi. Microorganisms can very easily contaminate a product through repeated consumer use. Even if a cosmetic preparation contains exquisite substances, it can turn into an unhealthy product through the inadvertent introduction of undesirable microorganisms.
As a standard procedure, many cosmetic houses use the standard microbial challenge test. In this test, samples of cosmetics are inoculated with test organisms and then inspected visually and by use of a plate count to determine if bacteria reduction has been attained. The microorganisms have been made available from the American Type Culture Consumer (ATCC), but some in-house resistant microorganisms are also tested. The most notorious strains include pseudomonas and other gram-negative microorganisms, gram-positive staphylococcus and various yeasts and molds. The testing time may run from two to three weeks to several months. The method also follows the CTFA and ASTM recommendation of two challenges, several weeks apart. Another very reliable test procedure has been the multiple challenges, whereupon all formulas are challenged to extinction; i.e. until microorganisms are routinely recovered from the test samples. A judgment is made on the minimal number of challenges that gives no recovery. Three successive positives may be considered an indication of failure with the system. The number of successful challenges required must be determined by an assessment of the overall susceptibility of the formula. This test was found useful for comparing different formulas, competitive as well as in-house. Our philosophy at Coty has been to offer consumers a well-preserved and a very safe product. Therefore, the selection of a suitable preservative system is of paramount importance in the other ingredients of the formula as well as the tamper-proof packaging.
Household Product Preservation
In household cleaning products, the most common mild-to-moderate alkalis (such as baking soda and ammonia), acids, household bleaches and detergents are used to disinfect and to do many cleaning jobs around the home and workplaces. The latest product form on the market is the wipe. Leading marketers such as Procter & Gamble and Clorox have introduced these wipes to the market with great success. In fact, according to Information Resources, Inc., Chicago, wipe sales have soared more than 900% during the past year. Clorox disinfecting wipes are made up of 0.14% dimethyl benzyl ammonium chloride, 0.145% dimethyl ethyl benzyl ammonium chloride and 99.710% “other ingredients.” These wipes are used to kill staph. and salmonella without bleach, which can damage some surfaces.
The Most Popular Preservatives
Here is a look at some of the most frequently-used preservatives for personal care and household cleaning products. Parabens include the mixture of various esters of benzoic acid (methyl, ethyl, propyl and butyl). It is the most popular mixture that has been used successfully to combat fungi and gram-positive bacteria. However, it shows poor activity against pseudomonas. It is effective over a wide pH range, although the optimum pH is 8. The parabens can be complemented with another preservative having special effects against gram-negative organisms.
Phenoxyethanol is a phenolic derivative that is active against predominantly gram-negative bacteria. It has a wide pH tolerance. It is water and alcohol miscible. Recommended concentration levels are 0.5-2%.
Imidazolidinyl urea is water-soluble and has a wide pH range tolerance. It exhibits broad-spectrum, anti-microbial activity when combined with parabens. The use of this preservative is restricted because it yields low levels of formaldehyde.
Diazolidinyl urea belongs to the Germall family of preservatives. Although a broad spectrum preservative, it acts predominantly against gram-negative bacteria. It is water soluble and can perform preservation between pH 3-9. Recommended concentration levels are 0.03-0.3%. It is also a formaldehyde donor.
Ethyl alcohol has excellent anti-microbial activity against bacteria and fungi. As a preservative, 15-20% is the recommended concentration.
Benzyl alcohol is a local anesthetic and is sometimes added to relieve itching, especially in cosmetic eye products. It is an efficient bacteriostatic agent. A concentration of 1-3% is recommended as a preservative. It is water-soluble at 1g/30ml.
Dehydroacetic acid is an effective bacteriostat and fungistat. It is water-soluble and effective within a pH of 5-6.
A mixture of N-butyl, isobutyl and isopropyl parabens (Liquapar) is primarily active against yeast, molds and some bacteria. It can tolerate a wide pH range. The typical usage level is 0.5-0.3%.
Potassium sorbate is primarily active against molds and yeasts. It is water-soluble with an optimum pH of up to 6.5.
Methyl, chloromethyl isothiazolinone and methyl isothiazolinone (Kathon CG) are active against bacteria, yeast and fungi. They are supplied as an aqueous solution, but for usage concentrations please contact the supplier. It can tolerate the entire pH range. The preservative is designed for rinse-off products such as shampoos and body washes.
DMDM hydantoin (Glydant) is a broad spectrum preservative, but less effective against yeasts. It is water soluble with an optimum pH 4.5-9.5.
Benzoic acid and its salt (sodium benzoate) have been used as preservatives in the food industry. Both are water-soluble with a recommended concentration of 0.1-0.2%. Their activity spectrum includes yeasts, some molds and bacteria.
Benzalkonium chloride is a quaternary compound having primary activity against gram-positives and some gram-negatives. It is soluble in water and alcohol with an optimum pH of 4-10. The usage concentration is 0.1-0.3%.
Quaternium 15 (Dowicil 200) is another quaternary broad spectrum preservative. It is water-soluble with a wide pH range (4-10).
Phenyl mercuric acetate is used in cosmetics, especially in eye products such as mascaras, where other preservatives fail. It is poorly soluble in water and soluble in hot ethanol. It is active against bacteria and fungi. As a preservative it is used in concentrations of 0.002-0.125%.
Chloroxylenol (Ottasept) is a halogenated phenolic compound with antibacterial and antifungal actions. It is alcohol soluble and poorly soluble in water. It tolerates a wide pH range. Recommended concentration is 0.2-0.8%.
Glutral (Ucarcide) is chemically glutaraldehyde. It is a broad spectrum preservative and soluble in water. Use concentration ranges from 0.02-0.2% of a 50% solution. It can remain active through a broad pH range.
Phenyl ethyl alcohol has a pleasant floral rose odor and is water soluble up to 2%. It is primarily active against gram-negative bacteria.
Sorbic acid is a mold and yeast inhibitor. It is also used as a fungistatic agent in foods, especially cheeses. It is slightly soluble in water, and soluble in alcohol. It becomes inactive above pH 6.2 and the optimum pH range is 2.5-6. Use concentration ranges from 0.10-0.30%.
2-Bromo-2-nitropropane-1, 3-diol (Bronopol) is an efficient broad-spectrum preservative with only some activity against yeast. It is water-soluble and stable in acid environments with an optimum pH of 6. It has not been a popular preservative in the U.S., because it is pH sensitive and has been observed to impart color to the product. However, it is present in most of the cosmetic products outside the U.S.
Chlorhexidine gluconate is a cationic compound, which limits its use. It is active against bacteria. The optimum stability pH is neutral but remains active between pH 5-8. It is also unstable at high temperatures and is incompatible with anionics and many gums. Usage levels range from 0.01-0.1%.
Salicylic acid is effective against bacteria and fungi. It is poorly water-soluble and discolors products that contain traces of iron. It is used in cosmetics as a keratolytic at high concentrations. Its optimum pH is 4-6 with a usage concentration of 0.1-0.5%.
Formaldehyde is an efficient preservative with a broad-spectrum activity against bacteria and fungi. It has not been a popular preservative because of the aldehyde sensitizing reactions in some subjects. It is sometimes used in rinse-off products. It becomes inactive in the presence of proteins, especially gelatin. Optimum pH is 3-10, with use concentration ranging from 0.05-0.2%.
Creating well-preserved cosmetics is a complex process. Each cosmetic house is determined to offer the consumer the best, purest and safest product. In order to achieve these goals, each company follows the CTFA and ASTM guidelines as well as its own testing procedures in order to offer a better product. One of the most important tests is to ensure the stable presence of chemical preservation at a certain level so that the product resists the growth of microorganisms. This should guarantee a product life of at least two years.
The chemist must pick the best preservative system which will not form complexes with ingredients present in the formula. The chemist should also conduct preservative stability tests with the plastic containers at ambient storage conditions. It is also necessary for the chemist to observe any physical changes in the product due to the interaction with plastic polymer coatings. The chemist should also verify the laboratory test results by comparing field-testing and analyzing consumer complaints.11 It is also very important to distinguish between the various chemical preservatives that are ideal for leave-on and rinse-off products. For this, the supplier can provide guidelines regarding preservatives individually.
The chemist should also take into account the use of various preservatives present in the individual raw materials selected for the final formula, which can have cumulative or detrimental effects on overall product performance. The detrimental effects may be perceived as irritation or complex formation, inactivation of main preservatives of the finished formula or causing instability as a whole. In this respect, herbal extracts, bioactives and many of the cosmetic actives containing different preservatives other than in the final product are well known for their complexity.
Looking for a new preservative system? A directory of materials can be found in the print version of Happi.
1. Butler, N.J., The microbial deterioration of cosmetics and pharmaceutical products in biodeterioration of materials, Elsevier, Amsterdam, 1968.
2. Kabara, Jon J., “Composition and structure of microorganisms,” Cosmetic and drug preservation, vol 1, 21-27, Marcel Dekker, Inc., New York.
4. Miyawaki, G.M., Patel, N.K. and Kosten- bauder, H.B., J.A. Ph. A., Sc. Ed., 48,315, 1959.
5. Lach, J. L., et al., J. A. Ph.A., Sc. Ed., 46, 615, 1957.
6. Kabara, Jon J., “The medium is the preservative,” Cosmetic & Toiletries, 63-67, March, 1981.
8. Routledge E.J., Parker J., Odum J., Sumpter J.P., “Some alkyl hydroxy benzoate preservatives (parabens) are estrogenic.” Toxicol Appl. Pharmacol 153:12-19, 1996.
9. Cosmoferm c/o Centerchem, Inc., Clover Ave., Norwalk, CT.
10. Citricidal Australia Pty Ltd (Fax: 61 754940788).
11. Cowen, R.A., “Relative merits of in-use and laboratory methods for the evaluation of antimicrobial products,” J.S.C.C. 25, 307-323, 1974.