Survey and health assessment of cosmetic products ... - Miljøstyrelsen

However, low water activity by itself may not be sufficient to kill
microorganisms. The survival of bacteria/microorganisms also depends on
other stresses imposed by the formula (acidic pH, lack of nutrients,
membrane-destabilising surfactants or chelating agents 4 , etc.) and storage
conditions including temperature. (Kabara & Orth, 1996)
3.4 pH control
Each organism has an optimum pH for growth. The growth rate of
microorganisms is generally favoured around neutral pH 7 and decreases at
acidic and alkaline conditions pH (Varvaresou et al., 2009).
The pH of a product may be lowered using inorganic or organic acids. Fatty
acids as e.g. lauric acid have an antimicrobial effect, and the free fatty acids in
a cosmetic product will contribute to the antimicrobial action of a formula,
especially at pH values < 4.5 (Kabara & Orth, 1996).
The ability of microorganisms to grow/survive also becomes increasingly
difficult as the pH increases. Products with pH values greater than pH 9 often
require little or no chemical preservatives. (Kabara & Orth, 1996)
3.5 Preservation of products with antimicrobial ingredients
3.5.1 Chelating agents
Removal of substrates and essential nutrients helps prevent the growth of
microorganisms. Chelating agents are used to bind metal ions that are
“unwanted” as they can cause deterioration in fragrance, colour, and
appearance of the cosmetic formulations. Binding of the metal ions interferes
with microbial growth as metal ions required for cell growth. (Kabara & Orth,
1996)
Chelating agents commonly used in cosmetic products are tetrasodium
EDTA, trisodium EDTA, and citric acid. EDTA is in itself an antimicrobial
agent, but also enhances the preservative action when combined with other
commonly used cosmetic preservatives such as parabens and quaternary
ammonium salts (Kabara & Orth, 1996).
3.5.2 Surfactants
A number of surfactants have antimicrobial action because they reduce the
surface tension and destabilise cell membranes. Different classes of
microorganisms appear to be affected differently by surfactants. The
following examples of surfactants have antimicrobial effects on different
microorganisms:
� Anionic surfactants (like sodium lauryl sulfate, ammonium lauryl
sulfate, sodium laureth sulfate).
� Nonionic surfactants (like polysorbate 80, sucrose laurate, or other
nonionic esters of fatty acids).
4
A chelating agent is defined as “Reacts and forms complexes with metal ions which
could affect the stability and/or appearance of cosmetics” according to the EU CosIng
database.
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