Table
II
Classes
of
Preservatives
with
Advantages
and
Disadvantages
Preservative
class
Advantages
Disadvantages
Organic
Acids
Benzoic Dehydroacetic
Salicylic
Sorbic
Good
activity
at
acid
pH
More
active
against
yeasts
and
molds.
Some
activity
against
bacteria.
Benzoates
are
used
in
carbonated
beverages.
Salicylic
acid
is
an
antimicrobial
active
ingredient
in
dandruff
and
acne
treatment
products.
Activity
is
pH
dependent
with
better
function
acidic
of
the
pKa:
Benzoic
acid
pKa
=
4.2
Dehydroacetic
acid
pKa
=
5.26
Sorbic
acid
pKa
=
4.76
Salicylic
acid
is
more
effective
with
pH
below
pH
3.7
(pKa
=
2.97)
Paraben
Esters
Methylparaben
Ethylparaben
Propylparaben
Butylparaben
Isobutylparaben
Active
against
Gram
positive
bacteria,
yeast,
and
mold.
Relatively
nonirritating
at
use
levels.
Some
esters
used
in
foods.
Not
effective
against
Gram-negative
bacteria
without
a
chelating
agent.
Inactivated
by
surfactants
above
the
critical
micelle
concentration.
More
effective
at
acid
pH.
Endocrine
issues
Possible
cancer
issues
Quaternary
Ammonium
Compounds
Benzalkonium
chloride
Benzethonium
chloride
Cetylpyridinium
chloride
Primarily
active
against
Gram
positive
bacteria.
Some
activity
against
Gram-negative
bacteria.
Incompatible
with
anionics
and
proteins.
Poor
activity
against
pseudomonads
without
chelating
agents.
More
active
above
pH
7
Formaldehyde
Donors
2-bromo-2-
nitropane-
1,3-diol
(BNPD)
Diazolidinyl
urea
DMDM
hydantoin
Imidazolidinyl
urea
Quaternium-15
Sodium
hydroxy-
methylglycinate
Broad
spectrum
of
antimicrobial
activity.
Donors
retain
activity
in
the
presence
of
surfactants.
Wide
pH
range
of
activity,
except
for
BNPD
which
is
not
stable
at
pH
6
Relatively
inexpensive
Possible
incompatibility
with
proteins.
Irritation/sensitization
issues.
Cancer
issues.
BNPD
use
has
decreased
since
the
1980s
due
to
the
potential
to
form
nitrosamines.
Regulatory
issues
(not
permitted
or
require
product
labeling
in
some
countries).
Alcohols
Ethyl
alcohol
Isopropyl
alcohol
Benzyl
alcohol 2,4-Dichlorobenzyl
Alcohol
Ethyl
and
Isopropyl
alcohols
have
broad
spectrum
of
antimicrobial
activity
at
high
concentrations
moderate
concentrations
(5%)
may
contribute
to
preservative
system.
Benzy
alcohol
is
antibacterial
and
antifungal
at
low
concentrations.
2,4-Dichlorobenzyl
alcohol
is
active
against
bacteria
and
viruses
and
is
used
in
throat
lozenges.
High
concentrations
(15%)
of
ethyl
alcohol
are
required
for
antimicrobial
action
(depending
on
system).
Ethyl
alcohol
is
volatile
and
may
evaporate
from
products
unless
this
is
prevented
by
packaging.
Alcohols
may
be
inactivated
by
nonionics.
Moderate
and
high
concentrations
may
cause
stinging
when
applied
to
skin.
Organic
Mercurials
Phenyl
mercuric
salts
Broad
spectrum
of
antimicrobial
activity
at
very
low
concentrations.
High
toxicity
and
irritancy.
Regulatory
issues
(allowed
in
eye-area
cosmetics
in
the
USA).
Inactivated
by
proteins
and
anionics
may
be
inactivated
by
nonionics.
Miscellaneous
Chloromethyl-
isothiazolinone
and Methylisothiazolinone Chlorphenesin
Antimicrobial
against
bacteria,
yeasts,
and
molds.
Isothiazolinones
are
effective
at
very
low
concentrations.
Chlorphenesin
is
relatively
nontoxic
and
is
approved
for
use
in
the
European
Union
(up
to
0.3%).
Isothiazolinones
may
cause
contact
dermatitis
and
are
inactivated
by
proteins,
high
pH,
and
bleach.
Phenoxyethanol
Rose
ether
fragrance.
Active
against
Gram-negative
bacteria
less
active
against
Gram
positive
bacteria.
Compatible
with
anionic
and
cationic
detergents
Inactivated
by
highly
ethoxylated
compounds
*Table
adapted
from
Orth. 14
489 Evolution and Challenges of Sustainability

490 JOURNAL OF COSMETIC SCIENCE
In 2004, Darbre et al. reported that parabens were found in human breast tumors.20 The
implication was that parabens were linked with cancer. These workers indicated that MP
may have been at higher levels than other paraben esters due to its more widespread use
in consumer products or due to its greater ability to be absorbed and/or resist hydrolysis
in body tissues. Unfortunately, no normal tissues were sampled in the subjects tested to
provide reference levels of parabens present in noncancerous tissues.14
The estrogenic activity of MP was already known because Nakagawa and Maldeus had
reported that parabens had estrogenic activity in rat hepatocytes in 1998.21 These workers
found that butylparaben (BP) had the most estrogenic activity of the paraben esters tested.
BP was significantly more estrogenic than MP. Nevertheless, the publication by Darbre and
coworkers shocked the cosmetic industry because it raised a possible link between parabens
and cancer. This was unsettling because parabens had been in use for over 50 years and
were the most used preservative in the cosmetic industry.14
An editorial by Harvey and Everett provided excellent perspective on the report by Darbre
and coworkers, because it explained that parabens have inherent estrogenic activity, and
that estrogen is a major factor in the growth and development of human breast cancer.22
They noted that long-term exposures due to the use of products containing parabens may
contribute to the bioburden of estrogenic materials in the body. Even though the cause-
and-effect relationship between parabens and breast cancer was not established, Harvey and
Everett concluded that unlike environmental exposures that may not be avoidable, individual
use of consumer products with parabens is preventable, and that the removal of estrogenic
formula components would eliminate one potential source of estrogenic materials. Goon,
Leow, and Goh observed that this was unfortunate because perception often becomes reality
to consumers.23 Many companies reacted to this concern by replacing parabens in products
with other preservatives and with multifunctional ingredients that have antimicrobial
activity to meet the perceived consumer demand for products that are safe.
In 2020, The Cosmetic Ingredient Review Expert Panel for Cosmetic Ingredient Safety
reported on the safety of 21 parabens as preservatives in cosmetic products. It was
concluded that “20 of the 21 parabens included in this report are safe in cosmetics in
the present practices of use and concentration described in this safety assessment when
the sum of the total parabens in any given formulation does not exceed 0.8%.”24 They
reported that the available data are insufficient to support a conclusion of safety for BP
in cosmetics.24 Currently, the position of the FDA is that “At this time, we do not have
information showing that parabens as they are used in cosmetics have an effect on human
health.”25 Although MP and PP continue to be popular preservatives in cosmetics, many
manufacturers are formulating products without parabens to avoid consumer perception
that parabens in cosmetics are unsafe.
In 2016, The US FDA issued a final rule establishing that OTC consumer antiseptic wash
products, such as deodorant or medicated soaps, containing certain active ingredients (e.g.,
Triclosan, Triclocarban, etc.) could no longer be marketed.26
Hand and bodywash manufacturers were no longer able to sell antibacterial soap and
washes with antibacterial active ingredients because they did not demonstrate that the
active ingredients were both safe for long-term daily use and more effective than plain soap
and water in preventing illness and the spread of certain infections. Thus, manufacturers
failed to provide data, or the information submitted was not sufficient for the FDA to
determine that these active ingredients are generally recognized as safe and effective.