Developing a robust preservation system is critical to maintaining the long term stability and safety of a formulation. This is especially difficult when developing global formulations due to the limited number of personal care preservatives that are globally approved. Currently there are only approximately 16 preservatives that are globally approved with unrestricted use (EU, USA, Japan).
What’s a preservative? It’s any chemical used to kill or prevent the growth of micro-organisms, preventing contamination or spoilage of a product (or raw material).
Properties of the ideal preservative:
- Global approval, particularly in the EU, USA and Japan
- Stable and effective over product shelf life
- Easy to use and handle
- Effective at target pH of product
- Raw material & formulation compatibility
- Readily soluble in water
- Heat Stable
- Non irritating
Classes of globally approved preservatives:
Problem Ingredients in Cosmetic Formulations
- Microbial nutrients: aloe, dipropylene glycol, plant extracts, sodium hyaluronate, vitamins
EU: aloe | dipropylene glycol | plant extracts | sodium hyaluronate | vitamins
- Preservative absorbers: Silica, kaolin, talc, titanium dioxide
EU: silica | kaolin | talc | titanium dioxide
- Preservative inactivators: lecithin, ethoxylated surfactants, xanthan gum, cellulose gum, polar oils (sunscreens)
EU: lecithin | xanthan gum | cellulose gum | polar oils
Recommended globally approved preservatives:
- Methylparaben, propylparaben, ethylparaben
EU: methylparaben | propylparaben | ethylparaben
- Phenoxyethanol, benzyl alcohol
EU: phenoxyethanol | benzyl alcohol
- Dehydroacetic, sorbic, benzoic and salicylic acids and their salts
EU: dehydroacetic acid | sorbic acid | benzoic acid | salicylic acid
- Isopropyl methyl phenol
Preservative potentiators are essential materials needed to boost the activity of globally approved preservatives. These materials significantly increase the antimicrobial activity of preservatives, but they normally have little or no activity when used alone. Classes of potentiators include chelators, acids, alcohols, diols, monoglycerides, ethers, metals, and peptides.
Chelators work by binding trace metals needed by micro-organisms to survive.
Recommended chelators include:
- Disodium EDTA – Edeta® BD by BASF (EU)
- Sodium Hexametaphosphate
- Sodium Citrate – Trisodium Citrate Dihydrate by Jungbunzlauer (EU)
- Sodium Phytate by Ankang Shi Mao Biotec/Deckner Consulting Services LLC (EU)
Diols work by increasing the penetration of preservatives into cell membranes of micro-organisms. Diols up to 6 carbons are water soluble and antimicrobial activity peaks around 8 carbons.
Recommended diols include:
- MP Diol by DuPont
- Pentylene Glycol – Hydrolite 5 by Symrise (EU)
- 1,2 Hexanediol – Hydrolite 6 by Symrise (EU)
- Caprylyl Glycol – Purolan OD by Lanxess Distribution (EU)
- 1,2 Hexanediol and Caprylyl Glycol – Symdiol 68 by Symrise. Synergism is claimed. (EU)
- 1,2 Decylene – SymClariol by Symrise (EU)
- 1, 2 Hexanediol, Caprylyl Glycol, Tropolone – Symdiol 68T by Symrise. Claimed synergistic blend. (EU)
- Glyceryl Monolaurate, 90% mono – Colonial Monolaurin by Colonial Chemical
- Propylene Glycol Heptanoate – Capmul 907P by Abitec
- Propylene Glycol Caprylate – Capmul 908P by Abitec
- Glyceryl Caprylate – Capmul 708G by Abitec
- Lactic acid (EU)
- Citric acid (EU)
- Usnic acid – EVOSINA® 100% (Sodium Usnate-MMP) by MMP International is a naturally occurring dibenzofuran derivative found in several lichen species. It is effective against gram positive organisms.
- Ethylhexylglycerin – Sensiva SC 50 by Schulke and Mayr (EU)
- Ethylhexylglycerin, Caprylyl Glycol – Sensiva SC 10 by Schulke and Mayr (EU). Better antimicrobial activity is claimed versus Symdiol 68.
- Copper, zinc, and silver salts
- Polylysine (JNC America) is a water soluble cationic peptide with a MW of 4700 produced by fermentation. It is a GRAS material that has been used for 20 years in foods.
- Nisaplin (Nisin-Danisco) is a polycyclic antibacterial peptide with 34 amino acid residues used as a food preservative. It is produced by fermentation and is effective against most gram positive organisms.
- Use combinations of materials that work by different mechanisms.
- All water based formulations should contain a chelator and diol.
- Don’t use metals with chelants.
- Use acids at or below their PKas for maximum activity.
- Use low PH to reduce preservative level.
- Cationic emulsions are significantly easier to preserve.
- Use multifunctional materials to help boost activity. Examples include chelants to improve product stability and Glyceryl Monolaurate as an emulsifier.
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