Delivering Sustainable Solutions to Improve Wellbeing

493 Evolution and Challenges of Sustainability
• It should be stable for the expected shelf-life/expiration date of the product.
• It should be compatible with other ingredients in the formulation and with packaging
materials.
• It should not affect the physical properties of the product (i.e., color, clarity, flavor, odor,
viscosity, texture, etc.)
• It should have a suitable oil/water (o/w) partition coefficient to ensure that an effective
concentration remains in the water phase because biochemical reactions and microbial
growth take place in aqueous systems or at the interface of o/w systems.
• It should inactivate microorganisms fast enough to prevent microbial adaptation.
• It should be safe to use. This applies to workers handling the preservative chemical
during manufacturing and to consumers using products with the preservative over a
period of months or years. Safe to use means that the preservative has no adverse effects
systemically or locally on skin.
• It should not induce cross-resistance with other antimicrobial agents or antibiotics.
• It should comply with governmental regulations.
• It should be sustainable and not have adverse environmental effects.
• It should not adversely affect the healthy skin microbiome.
• It should be cost-effective to use.
It may be difficult, or even impossible, to have a preservative or a multifunctional ingredient
with antimicrobial action that is effective against all types of microorganisms (to protect
formulations) and that does not adversely affect the healthy skin microbiome. Nevertheless,
knowing the characteristics of an ideal preservative may help provide the basis for selection
of the most suitable antimicrobials to meet preservation requirements for products that are
natural/organic, consumer friendly, environmentally friendly, and sustainable.
THE PRESERVATIVE SYSTEM CONCEPT
The antimicrobial action of a formulation generally is thought to be due solely to the
preservative chemicals used however, preservatives do not act independently of other
ingredients in the formula. The “preservative system” of a product includes specific
chemical preservatives (if present) and the physicochemical composition of the product,
which includes factors such as the pH, a
w ,redox potential, alcohols, surfactant type, and
concentration, chelating agents, antioxidants, lack of nutrients, and interfering materials
(e.g., talc and bentonite) that may affect the preservative efficacy of a formulation, and
protective packaging.33
All ingredients may have more than one function in product formulations. For example,
organic acids may reduce the pH, affect viscosity, change fragrance character, and exert
antimicrobial action QACs may contribute to skin feel or hair conditioning and provide
antimicrobial activity alcohols may help solubilize ingredients and contribute to the
preservative system antioxidants may help preserve fragrance character and product color
and may alsp have antimicrobial action. Types of ingredients that may contribute to the
preservative system of cosmetic and drug products are presented in Table III and are
discussed more fully in sections below.
Adequate protective packaging is an essential part of a product’s preservative system.
Products with conventional preservatives and preservative-free products require protective
packaging to help prevent microbial contamination during consumer use. Different

494 JOURNAL OF COSMETIC SCIENCE
closures (i.e., screwcap, flip top, pump, etc.) allow different amounts of human contact with
the product and allow different amounts of contamination/water intrusion during use of
shampoos, conditioners, and body washes when bathing/showering. In addition, packaging
for low a
w -based preservative systems must be designed to prevent moisture entry that
could increase the a
w to a level that may allow microbial growth. Stability studies must
be done under humid conditions to demonstrate that the packaging is capable of resisting
moisture so that the formula remains at the desired low a
w .34 Additional information on
cosmetic packaging may be found in the book chapter on “The role of packaging in product
preservation” by Brannan.35
PRESERVATIVE-FREE PRODUCTS
The cosmetic industry has been transitioning from traditional preservative systems to
preservative-free formulations for several decades. The term “preservative-free” means
without preservative chemicals. It is possible to make preservative-free cosmetics and
drugs if they are sterilized, packaged, and stored properly. Examples include a sterilized
Table III
Formula Ingredients That may be Part of the Preservative System of a Product
Ingredient Function
Preservatives Kill susceptible MO rapidly when used at adequate levels.
Acids and Alkalis Reduce growth of many microorganisms at pH 5 or pH 9.
Alcohols (ethyl alcohol, isopropyl alcohol) May increase membrane permeability, precipitate proteins and
inactivate enzymes 25% will prevent growth of bacteria,
yeasts, and molds.
Quaternary Ammonium Compounds
(benzalkonium chloride, benzethonium
chloride, cetylpyridinium chloride)
Effective against many Gram-positive bacteria at 0.1%
Gram-negative bacteria are more resistant than Gram
positive bacteria.
Anionic Surfactants (ammonium lauryl
sulfate, sodium lauryl ether sulfate)
Many Gram-positive bacteria are more susceptible than
Gram-negative bacteria. Micellular solubilization lowers
effective concentration of lipophilic preservatives.
Fatty Acids and Glyceryl Esters (glyceryl
monolaurate)
Antibacterial at 0.5%–2.0%, potentiated by chelating agents.
Polyols (glycerin, propylene glycol, butylene
glycol, sorbitol, pentylene glycol)
Lower aw to make it difficult for microorganisms to maintain
homeostasis.
Water-soluble solutes (sugars, salts, amino
acids, small peptides)
Lower aw to make it difficult for microorganisms to maintain
homeostasis.
Chelating agents (tetrasodium EDTA,
Citric acid)
0.1%–0.3% EDTA potentiates antimicrobial action against
Gram-negative bacteria by permeabilization synergy.
Phenolic antioxidants MIC values of 70 ppm for Staphylococcus aureus, 150 ppm for
Escherichia coli and Candida albicans. Antibacterial action
may be eliminated by 1.5%–3% vegetable oil.
Fragrances and aroma chemicals 0.1%–1% may have additive or synergistic killing effect with
other preservative system ingredients.
Botanicals (green tea, rosemary, willow
bark)
Flavonoids, terpenoids, and phenolic compounds effective
against many microorganisms.
Enzymes and Microbial Ferments Glucose oxidase and lactoperoxidase enzymes. Lactobacillus,
Leuconostoc, and Saccharomyces ferments.
Combinations of ingredients Experimentation needed to show which combinations work
best in a formulation.
*Table adapted from Orth.14

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493 Evolution and Challenges of Sustainability
• It should be stable for the expected shelf-life/expiration date of the product.
• It should be compatible with other ingredients in the formulation and with packaging
materials.
• It should not affect the physical properties of the product (i.e., color, clarity, flavor, odor,
viscosity, texture, etc.)
• It should have a suitable oil/water (o/w) partition coefficient to ensure that an effective
concentration remains in the water phase because biochemical reactions and microbial
growth take place in aqueous systems or at the interface of o/w systems.
• It should inactivate microorganisms fast enough to prevent microbial adaptation.
• It should be safe to use. This applies to workers handling the preservative chemical
during manufacturing and to consumers using products with the preservative over a
period of months or years. Safe to use means that the preservative has no adverse effects
systemically or locally on skin.
• It should not induce cross-resistance with other antimicrobial agents or antibiotics.
• It should comply with governmental regulations.
• It should be sustainable and not have adverse environmental effects.
• It should not adversely affect the healthy skin microbiome.
• It should be cost-effective to use.
It may be difficult, or even impossible, to have a preservative or a multifunctional ingredient
with antimicrobial action that is effective against all types of microorganisms (to protect
formulations) and that does not adversely affect the healthy skin microbiome. Nevertheless,
knowing the characteristics of an ideal preservative may help provide the basis for selection
of the most suitable antimicrobials to meet preservation requirements for products that are
natural/organic, consumer friendly, environmentally friendly, and sustainable.
THE PRESERVATIVE SYSTEM CONCEPT
The antimicrobial action of a formulation generally is thought to be due solely to the
preservative chemicals used however, preservatives do not act independently of other
ingredients in the formula. The “preservative system” of a product includes specific
chemical preservatives (if present) and the physicochemical composition of the product,
which includes factors such as the pH, a
w ,redox potential, alcohols, surfactant type, and
concentration, chelating agents, antioxidants, lack of nutrients, and interfering materials
(e.g., talc and bentonite) that may affect the preservative efficacy of a formulation, and
protective packaging.33
All ingredients may have more than one function in product formulations. For example,
organic acids may reduce the pH, affect viscosity, change fragrance character, and exert
antimicrobial action QACs may contribute to skin feel or hair conditioning and provide
antimicrobial activity alcohols may help solubilize ingredients and contribute to the
preservative system antioxidants may help preserve fragrance character and product color
and may alsp have antimicrobial action. Types of ingredients that may contribute to the
preservative system of cosmetic and drug products are presented in Table III and are
discussed more fully in sections below.
Adequate protective packaging is an essential part of a product’s preservative system.
Products with conventional preservatives and preservative-free products require protective
packaging to help prevent microbial contamination during consumer use. Different

494 JOURNAL OF COSMETIC SCIENCE
closures (i.e., screwcap, flip top, pump, etc.) allow different amounts of human contact with
the product and allow different amounts of contamination/water intrusion during use of
shampoos, conditioners, and body washes when bathing/showering. In addition, packaging
for low a
w -based preservative systems must be designed to prevent moisture entry that
could increase the a
w to a level that may allow microbial growth. Stability studies must
be done under humid conditions to demonstrate that the packaging is capable of resisting
moisture so that the formula remains at the desired low a
w .34 Additional information on
cosmetic packaging may be found in the book chapter on “The role of packaging in product
preservation” by Brannan.35
PRESERVATIVE-FREE PRODUCTS
The cosmetic industry has been transitioning from traditional preservative systems to
preservative-free formulations for several decades. The term “preservative-free” means
without preservative chemicals. It is possible to make preservative-free cosmetics and
drugs if they are sterilized, packaged, and stored properly. Examples include a sterilized
Table III
Formula Ingredients That may be Part of the Preservative System of a Product
Ingredient Function
Preservatives Kill susceptible MO rapidly when used at adequate levels.
Acids and Alkalis Reduce growth of many microorganisms at pH 5 or pH 9.
Alcohols (ethyl alcohol, isopropyl alcohol) May increase membrane permeability, precipitate proteins and
inactivate enzymes 25% will prevent growth of bacteria,
yeasts, and molds.
Quaternary Ammonium Compounds
(benzalkonium chloride, benzethonium
chloride, cetylpyridinium chloride)
Effective against many Gram-positive bacteria at 0.1%
Gram-negative bacteria are more resistant than Gram
positive bacteria.
Anionic Surfactants (ammonium lauryl
sulfate, sodium lauryl ether sulfate)
Many Gram-positive bacteria are more susceptible than
Gram-negative bacteria. Micellular solubilization lowers
effective concentration of lipophilic preservatives.
Fatty Acids and Glyceryl Esters (glyceryl
monolaurate)
Antibacterial at 0.5%–2.0%, potentiated by chelating agents.
Polyols (glycerin, propylene glycol, butylene
glycol, sorbitol, pentylene glycol)
Lower aw to make it difficult for microorganisms to maintain
homeostasis.
Water-soluble solutes (sugars, salts, amino
acids, small peptides)
Lower aw to make it difficult for microorganisms to maintain
homeostasis.
Chelating agents (tetrasodium EDTA,
Citric acid)
0.1%–0.3% EDTA potentiates antimicrobial action against
Gram-negative bacteria by permeabilization synergy.
Phenolic antioxidants MIC values of 70 ppm for Staphylococcus aureus, 150 ppm for
Escherichia coli and Candida albicans. Antibacterial action
may be eliminated by 1.5%–3% vegetable oil.
Fragrances and aroma chemicals 0.1%–1% may have additive or synergistic killing effect with
other preservative system ingredients.
Botanicals (green tea, rosemary, willow
bark)
Flavonoids, terpenoids, and phenolic compounds effective
against many microorganisms.
Enzymes and Microbial Ferments Glucose oxidase and lactoperoxidase enzymes. Lactobacillus,
Leuconostoc, and Saccharomyces ferments.
Combinations of ingredients Experimentation needed to show which combinations work
best in a formulation.
*Table adapted from Orth.14

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495 Evolution and Challenges of Sustainability
preservative-free lotion in a unit-dose package and a 500 mL bottle of sterile dextrose for
infusion. Preservative-free cosmetics and drugs are not new and have been sold for many
years, often without the manufacturer knowing why they did not require use of traditional
preservatives. Antidandruff shampoos with salicylic acid around pH 3.5, sterile eye-drop
solutions in protective packaging, antibiotic ointments, and anhydrous/low a
w products,
including powders (i.e., baby powder and pressed powder), oils, and waxes (i.e., lipsticks and
stick deodorants) may not require preservatives. These products are satisfactorily preserved
because of their physicochemical composition and/or packaging.31
Although cosmetics and many topical drug products are not intended to be sterile, adequately
preserved aqueous products in multiple-use containers have a preservative system that
makes them self-sterilizing36 or bacteriostatic/fungistatic for low a
w formulations in which
the physicochemical environment (e.g., lack of water availability) will not allow growth.
It has not been easy to replace parabens with alternative preservatives or multifunctional
ingredients and retain the same level of preservative efficacy in some formulations. Self-
preserving products may be developed by understanding the principles of preservation and
the use of hurdle technology37 to meet adequate preservative efficacy test acceptance criteria.
HURDLE TECHNOLOGY
“Hurdle technology” involves the application of the principles of preservation to reduce or
eliminate the use of traditional preservatives to achieve “mild preservation” of products.37
Hurdle technology is commonly used to reduce preservative requirements or to create
preservative-free cosmetic products by use of low or high pH, low a
w ,surfactants, phenolic
antioxidants, chelating agents, aroma chemicals, alcohols, lack of readily fermentable
carbohydrates (e.g., nutrients), multifunctional ingredients that have antimicrobial activity,
and combinations of these elements to achieve a mild preservative system along with
protective packaging, as follows.
HURDLE TECHNOLOGY: USE OF LOW OR HIGH PH
Microorganisms that can grow in aqueous ingredients and cosmetic products and which
cause infections generally grow best around neutrality (i.e., pH 7). The rate of growth of
microorganisms usually decreases as the pH departs from the optimum pH for growth for
each type of microorganism because they must expend energy to maintain homeostasis as
the pH becomes more acid or more alkaline. Many yeasts and molds and some bacteria (e.g.,
lactic acid bacteria) can tolerate acidic pH conditions, with a pH 4.0.38 The microorganisms
that often cause problems in consumer products may be metabolically injured (stressed) by
extreme pH conditions in which the pH is less than pH 4 or greater than pH 10. The pH
requirements of some types of microorganisms are listed in Table IV.
Formulas with a low pH may be achieved by addition of naturally occurring organic
acids as is done with alpha-hydroxy acid exfoliants (i.e., glycolic acid), facial washes/acne
treatment products with beta-hydroxy acids (i.e., salicylic acid), and athlete’s foot products
(i.e., undecylenic acid), as well as with products containing microbial ferments (i.e., lactic
acid), acidulants (i.e., gluconolactone), and pH lowering chemicals (i.e., citric acid). pH
values around pH 3.5–4.0 may be obtained with aluminum salts used in antiperspirants.
Low pH products may be adequately preserved without traditional preservative chemicals.

496 JOURNAL OF COSMETIC SCIENCE
Formulas with a high pH (e.g., pH 9) may be achieved by the addition of sodium
thioglycolate, as is done for permanent wave products and hair relaxers. Alkaline agents
such as NaOH or triethanolamine may be used to increase the pH to pH 9, and this
makes it more difficult for bacteria to survive because they need to expend energy to
maintain their intracellular pH/homeostasis. For example, liquid soaps with an alkaline
pH (pH 9.5–10.5) present a hostile environment for growth of microorganisms due to the
chaotropic (i.e., membrane destabilizing) effect of ionized fatty acids and the free alkalinity
due to NaOH.11 High pH products such as liquid soaps may be adequately preserved
without added preservative chemicals.
HURDLE TECHNOLOGY: USE OF LOW WATER ACTIVITY
Water is a requirement for the growth of all known living organisms. Formulations that
limit the availability of water help prevent microbial growth because each type of bacteria,
yeast, and mold has an optimal a
w and a range of a
w values for growth under any given set
of environmental conditions (e.g., nutrients available, temperature, pH, etc.).39 Formulators
may lower the a
w in a formulation by adding polyols (i.e., glycerin, sorbitol, propylene
glycol, butylene glycol, and pentylene glycol) and water-soluble solutes (i.e., salts, protein
hydrolysates/ammino acids, short-chain fatty acids, sugars, etc.) to achieve the desired a
w .
Unfortunately, use of effective levels of these solutes often interferes with the aesthetics of the
product (e.g., skin feel, rub-in time, tackiness, etc.). One does not need to add enough polyols
or water-soluble solutes to reach the minimum a
w values for specific microorganisms because
just adding enough to lower the a
w to 0.97 will prevent growth of pseudomonads—a major
problem in aqueous products—and this reduced a
w hurdle will work with the other hurdles
in the preservative system to prevent growth of bacteria, yeasts, and molds. The minimum
a
w values for several types of microorganisms are presented in Table V.
Low a
w products may interfere with the ability of microorganisms to grow, and the low
water availability may slow metabolism to decrease the rate of killing action by some
preservatives. Such low a
w products include eyeliners, face powders, lip rouge, lip gloss,
lipstick, and mascaras and were termed “atypical products” because different methods of
preservative efficacy testing (e.g., the use of reduced numbers of microorganisms in the
inoculum, reduced volume of inoculum, surface sampling—as opposed to taking an aliquot
from an evenly dispersed/mixed aqueous sample—and use of different sample diluents),
and different acceptance criteria may be required.40 Even if such makeup products require
“relaxed” acceptance criteria, they should be bacteriostatic/fungistatic (e.g., they should
not allow microbial growth) or be slowly bactericidal/fungicidal, and they must have an
acceptable microbial load—an aerobic plate count (APC) 100 cfu/g (10 cfu/g preferred),
or PCPC limits of 1,000 cfu/g for topical products and an APC 500 cfu/g for eye-area
and baby products,41 and no objectionable microorganisms.
Table IV
pH Requirements for Types of Microorganisms.
Type of microorganism Typical pH range for growth
Many common bacteria pH 5–9
Lactic acid bacteria pH 3.5–8.5
Many yeasts and molds pH 4.5–9
*Table adapted from Orth.31

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491 Evolution and Challenges of Sustainability
In recent years, there has been a trend by many manufacturers to introduce products into
international markets. The US has fewer regulations for the use of preservatives in finished
consumer products than many other countries however, the FDA does require that
manufacturers substantiate that cosmetic products are safe, and that drug products are safe and
effective. The European Union, Health Canada, and Japan’s Ministry of Health and Welfare
have published directives/lists of preservatives, with allowed concentrations and restrictions
with respect to use on children, oral use, and leave-on or rinse-off products. Websites for the
European Union (Annex V), Health Canada, and Japan Ministry of Health provide up-to-date
information on levels of preservatives that may be used and restrictions that may apply to specific
product categories. These resources may be used to develop a list of “global preservatives” and
the allowed concentrations that may be used in products marketed internationally.14
Additional information on historical developments in product preservation and cosmetic
microbiology may be found in publications by Curry,27 Garrett and Orth,3 and Orth11 for
the United States, by Russell28 for the United Kingdom, and by Fukubayashi29 for Japan.
CHANGING USE OF PRESERVATIVES IN COSMETICS
The evolution of cosmetic preservation over the past 75 years has involved transitioning
from traditional preservative systems containing combinations of preservatives in aqueous
formulas to application of the principles of preservation to use ingredients that may replace
some or all the traditional preservatives in many formulas. Preservative-free products are
consumer and environmentally friendly because they have no issues due to preservatives
such as irritation, sensitization, endocrine modulation, cross-resistance with antibiotics,
carcinogenicity, and effects on the environment. Also, preservative-free products have no
restrictions or regulatory requirements for preservatives that limit marketing in any country.
Over the past several decades, ingredient suppliers have worked with manufacturers to
develop reduced preservative or preservative-free formulations by providing multifunctional
ingredients—chemicals that are not classified as preservatives, but which have antimicrobial
action that adds to the preservative system. Such multifunctional ingredients include glyceryl
monoesters (e.g., glyceryl monolaurate, glyceryl monocaprylate, and glyceryl caprylate)
that aid emulsification, humectants (e.g., ethylhexylglycerin and capryl glycol) that help
moisturize skin, polyols (e.g., butylene glycol, glycerin, propylene glycol, pentylene glycol,
and sorbitol) that moisturize skin and lower the water activity (a
w ),botanicals (e.g., willow
bark extract, turmeric, and sage), phenolic antioxidants that stabilize formulas by scavenging
free radicals, aroma chemicals (e.g., essential oils and phenoxyethanol) that contribute to the
fragrance, ferments (e.g., Lactobacillus ferments) and enzymes. Multifunctional ingredients
and the physicochemical composition of the formula comprise the “invisible preservative
system” that can reduce preservative requirements in conventional formulations that
contain preservatives, or that may be able to replace preservatives in preservative-free (self-
preserving) formulations.30 Formulation of preservative-free products may be accomplished
with an understanding of the principles of preservation.
PRINCIPLES OF PRESERVATION
Bacteria, yeasts, and molds are ubiquitous in nature, and they will grow in any environment
that provides sufficient moisture, appropriate nutrients, and suitable conditions for growth.

492 JOURNAL OF COSMETIC SCIENCE
The physical and chemical requirements for microbial growth include suitable temperature,
pH, a
w ,substrates/nutrients, oxygen (or the proper oxidation/reduction potential), organic
growth factors (which are needed by some bacteria), and freedom from harmful radiation
and chemicals (e.g., preservatives and antibiotics). Cosmetic ingredients and finished
products provide a wide range of organic and inorganic compounds that will support
microbial growth when water is present. Interestingly, the principles of preservation are
just the opposite of the requirements for microbial growth, which means that application
of these principles prevents bacteria from having access to the things they need, and use of
inhibitory agents (i.e., preservatives/biocides) causes their death.11 Use of these principles to
develop adequately preserved products helps manufacturers meet environmental concerns
and consumer demands for products that are free of chemicals recognized as preservatives.31
Preventing unnecessary microbial load, or bioburden, of the process stream is an
important consideration for making products in accordance with GMPs. This is the reason
manufacturers have microbial specifications (i.e., limits) for raw materials—to minimize
the microbial load in order to maintain microbiological control of the process, because
smaller populations of any specific microorganism require shorter times to kill than
larger populations with any given killing treatment (e.g., heat, chlorination, preservatives,
etc.).11Suppliers of cosmetic ingredients control the microbial load by removal of “bad”
components and avoiding contamination of raw materials obtained from natural sources,
including botanicals and materials obtained in mining operations (e.g., talc, clays, and salts).
The time/temperature parameters involved in preparing raw materials that have aqueous
steps in preparation (e.g., plant extracts and protein powders) are controlled to prevent
microbial growth. Finished product manufacturers prevent microbial growth by use of
adequate preservative systems in products and use of validated manufacturing procedures,
often using Hazard Analysis Critical Control Point (HACCP),32 to ensure microbiological
control of each step in manufacturing from receipt and storage of raw materials, cleaning
and sanitization of equipment, production of the product, packaging, product testing,
and storage prior to shipment to the trade.33 Selection of the proper antimicrobials and
concentrations needed are critical for adequate product preservation, and understanding the
characteristics of the ideal preservative provides the basis for this.
THE IDEAL PRESERVATIVE
There has been an evolution of the characteristics of the “ideal preservative” that have been
identified over the past 75 years to incorporate both positive and negative characteristics,
including inactivating microorganisms quickly enough to prevent adaptation, no cross-
resistance with other preservatives or antibiotics, no negative environmental issues, no
adverse effects on the skin microbiome, and sustainability. The ideal preservative is one that
is both safe and effective for killing all types of microorganisms in all types of formulations,
but it has never been found.14 The reason for this is that no single preservative meets all the
characteristics of the ideal preservative, which are:
• It should have a broad spectrum of activity, which means that it would be effective
against all types of microorganisms so that it could be used as the only preservative in
a formulation.
• It should be effective at low concentrations and be active over the range of pH values
used in cosmetics and drugs.

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