487 Evolution and Challenges of Sustainability
Wolven and Levenstein also performed challenge tests and concluded that “regardless of
the method employed to demonstrate preservative efficacy, no growth should occur after
seven days.”8 This is an important point because it means that preservative efficacy testing
should show a ≥6-log reduction in 7 days. The follow-up test conducted by Wolven and
Levenstein also revealed that liquid eyeliners were contaminated.
Surveys were performed to determine if eye-area cosmetics were contaminated. In 1975,
Wilson, Julian, and Ahearn found that eye-area cosmetics generally were not contaminated
when sold, but that they became contaminated during use by consumers.9 It was alarming
to find Pseudomonas spp. in eye-area products because these microorganisms may cause
serious eye infections. Ahearn et al. reported that mascaras containing only parabens or
imidazolidinyl urea appeared to be less effective in preventing microbial growth than
mascaras preserved with mercury-containing preservatives.10 These findings helped
provide support for regulatory approval of mercury-containing preservatives such as phenyl
mercuric acetate in eye-area cosmetics in the United States.11
The two decades after the report by Kallings and coworkers were designated as the “Golden
Age of Cosmetic Microbiology” because it was a time in which many microbiologists were
employed to conduct surveys of cosmetic and pharmaceutical products, improve compliance
with current good manufacturing practices (GMPs), perform preservative efficacy tests to
ensure that products were adequately preserved, and conduct studies in support of OTC
drugs. During this time, the United States Pharmacopoeia (USP) published methods for
assessing the adequacy of preservation12 and the CTFA Microbiological Committee (now
the Personal Care Product Council [PCPC] Microbiological Committee) recommended
preservative efficacy testing guidelines with samplings at 1 or 2 days, and at 7, 14, and 28
days.13 USP and PCPC methods of preservative efficacy testing are in use today.
Formulators learned what worked in their formulations by experience, and combinations of
preservatives—typically methylparaben (MP) and propylparaben (PP) with a formaldehyde
donor—were the most popular preservatives used in cosmetics. Preservatives that have been
used frequently in cosmetic and drug formulations from the 1970s to date are presented
in Table I.
When discussing preservatives, it often is helpful to consider their functionality in terms of
preservative class (e.g., organic acids and their salts, paraben esters, quaternary ammonium
compounds [QACs], formaldehyde donors, alcohols, organic mercurials, and miscellaneous),
because this is a way of relating chemical structure with the antimicrobial spectrum,
advantages, and disadvantages of the different types of preservatives.14 Classes of many
preservatives along with their advantages and disadvantages are presented in Table II.
Products marketed in the 1970s and after generally have been well-preserved. Creams,
lotions, and shampoos made by several major cosmetic companies were purchased, and
preservative efficacy tests were performed on them. The products tested were adequately
preserved because the preservative systems in these products killed the test bacteria quickly
(e.g., preservative systems killed 106–107 cfu/mL of some test bacteria within a couple of days
and all bacteria along with 105–106 cfu/mL yeasts and molds were killed within a week).15
These products met the preservative requirements set by Wolven and Levenstein8 because
they showed no growth of the test organisms after seven days. Frequently, P. aeruginosa was
not recovered at any time point during preservative efficacy testing—not even initially
at the time 0 sampling (i.e., within 5 minutes after inoculation). It was later learned that
MP and chelating agents including acrylic acid homopolymer/copolymers or EDTA, which
Wolven and Levenstein also performed challenge tests and concluded that “regardless of
the method employed to demonstrate preservative efficacy, no growth should occur after
seven days.”8 This is an important point because it means that preservative efficacy testing
should show a ≥6-log reduction in 7 days. The follow-up test conducted by Wolven and
Levenstein also revealed that liquid eyeliners were contaminated.
Surveys were performed to determine if eye-area cosmetics were contaminated. In 1975,
Wilson, Julian, and Ahearn found that eye-area cosmetics generally were not contaminated
when sold, but that they became contaminated during use by consumers.9 It was alarming
to find Pseudomonas spp. in eye-area products because these microorganisms may cause
serious eye infections. Ahearn et al. reported that mascaras containing only parabens or
imidazolidinyl urea appeared to be less effective in preventing microbial growth than
mascaras preserved with mercury-containing preservatives.10 These findings helped
provide support for regulatory approval of mercury-containing preservatives such as phenyl
mercuric acetate in eye-area cosmetics in the United States.11
The two decades after the report by Kallings and coworkers were designated as the “Golden
Age of Cosmetic Microbiology” because it was a time in which many microbiologists were
employed to conduct surveys of cosmetic and pharmaceutical products, improve compliance
with current good manufacturing practices (GMPs), perform preservative efficacy tests to
ensure that products were adequately preserved, and conduct studies in support of OTC
drugs. During this time, the United States Pharmacopoeia (USP) published methods for
assessing the adequacy of preservation12 and the CTFA Microbiological Committee (now
the Personal Care Product Council [PCPC] Microbiological Committee) recommended
preservative efficacy testing guidelines with samplings at 1 or 2 days, and at 7, 14, and 28
days.13 USP and PCPC methods of preservative efficacy testing are in use today.
Formulators learned what worked in their formulations by experience, and combinations of
preservatives—typically methylparaben (MP) and propylparaben (PP) with a formaldehyde
donor—were the most popular preservatives used in cosmetics. Preservatives that have been
used frequently in cosmetic and drug formulations from the 1970s to date are presented
in Table I.
When discussing preservatives, it often is helpful to consider their functionality in terms of
preservative class (e.g., organic acids and their salts, paraben esters, quaternary ammonium
compounds [QACs], formaldehyde donors, alcohols, organic mercurials, and miscellaneous),
because this is a way of relating chemical structure with the antimicrobial spectrum,
advantages, and disadvantages of the different types of preservatives.14 Classes of many
preservatives along with their advantages and disadvantages are presented in Table II.
Products marketed in the 1970s and after generally have been well-preserved. Creams,
lotions, and shampoos made by several major cosmetic companies were purchased, and
preservative efficacy tests were performed on them. The products tested were adequately
preserved because the preservative systems in these products killed the test bacteria quickly
(e.g., preservative systems killed 106–107 cfu/mL of some test bacteria within a couple of days
and all bacteria along with 105–106 cfu/mL yeasts and molds were killed within a week).15
These products met the preservative requirements set by Wolven and Levenstein8 because
they showed no growth of the test organisms after seven days. Frequently, P. aeruginosa was
not recovered at any time point during preservative efficacy testing—not even initially
at the time 0 sampling (i.e., within 5 minutes after inoculation). It was later learned that
MP and chelating agents including acrylic acid homopolymer/copolymers or EDTA, which
