Creative Developments (Cosmetics) Limited

Preservatives SPC 2000

With today’s emphasis on cosmetic product safety and lack of irritation in use it is an anomaly that toxic substances are added to the majority of compositions. However these toxic substances are added to preserve the product from microbial contamination and a much greater potential for causing harm to the consumer. However the phrase “as much as necessary – as little as possible” is particularly pertinent to the subject of cosmetic preservation and great efforts are made to keep the amount necessary to the minimum.

This may be achieved in various ways; the formulating chemist can reduce the product potential for supporting microbial growth by reducing the amount of free water in the product; by including materials that have antimicrobial properties although not regarded as preservatives and by careful attention to the product pH. The manufacturer can apply rigorous standards of hygiene and use HACCP techniques for identifying critical points in plant design and stages in manufacture. The suppliers of preservatives have invested heavily in investigating potential synergy in mixtures of preservatives, which also contributes to a reduction in the quantities used. However, despite the use of these techniques, if the product contains water it is almost invariably going to require preservation and the materials used must comply with legislation in all the markets intended for its eventual sale.

Reducing a product’s potential for supporting microbial growth is termed hurdle technology and this technique was described by Kabara and Orth [REF 1] at Preservatech 1998. Limiting water availability is one of the most effective hurdles. This can be achieved by the addition of salts, polyols, sugars, protein hydrolysates and amino acids and is more effective in controlling gram negative bacteria than yeast and moulds. Reducing a product pH to less than 5.0 is effective against most bacteria but not against yeast and moulds. The use of surfactants can be a positive help or may be detrimental to product preservation. If surfactants are present at a level above their critical micelle concentration (CMC) they may enclose the preservative within the micelle. If at lesser level they may solubilise the preservative and also render the organism’s protective membrane more susceptible to attack. Anionic fatty acid soaps have a weak biocidal activity in alkaline conditions. Many cationic surfactants are very effective, however some are classified as preservatives and have very low permitted levels according to EU legislation. Kabara and Orth describe many other methods of erecting hurdles to microbial growth and although not every hurdle will be suitable for every product it is a worthwhile concept.

One well-known hurdle is propylene glycol. It reduces water-availability and is also a useful co-solvent for many preservatives that have low water-solubility. Lyondell has undertaken studies of the antimicrobial properties of all the major glycols to be found in cosmetic products and compared the results with those obtained for MP Diol, the Lyondell trade name for methyl propanediol. The minimum inhibitory concentration (MIC) and the minimum lethal concentration (MLC) of each glycol against nineteen species of bacteria and seven fungal species were determined. The full report is available from Lyondell. In summary it shows that MP Diol has comparable antimicrobial activity to 1,3-butylene glycol and is more effective than propylene glycol.

Dragoco has also introduced a glycol with antimicrobial properties. Trade named Hydrolite-5 chemically it is 1,3-pentanediol and its INCI name is pentylene glycol. It is both water and oil-soluble and is intended as a moisture-binding additive with antimicrobial properties. Dragoco also market Fungicide DA, an undecylenamide DEA with fungicidal properties and suitable for shampoos, foam baths and shower-gels. Fungicide UMA is undecylenamide MEA and is used against dandruff, acne and in foot care, and Dragocide Forte, a mixed preservative system - see table. Shulke & Mayr supply a glycerin-ether under the trade name Sensiva SC50; its INCI designation is octoxyglycerin and it is very effective against Gram-positive bacteria. The same company supplies a number of preservatives and preservative mixtures that are summarised in Table 1.

HACCP is the acronym for Hazard Analysis Critical Control Point and the concept is based on designing a thorough hazard analysis plan to build safety and quality into the process [REF. 2]. When applied to microbiology it should identify all critical control points that attract, encourage and protect microbial proliferation at every stage of the product design and manufacture. This excellent paper identifies the seven basic principles of HACCP and gives a step-by-step guide to its implementation. The first critical control point refers to the ingredients including water, surfactants and botanical extracts. Plant design, cleaning and sanitising, processing steps and packaging materials are all part of the first basic principle of identifying potential hazards and preventative measures. The last step is to verify that the HACCP system is working correctly.

Despite hurdle technology, HACCP and careful attention to manufacturing hygiene a preservative is still going to be necessary in the majority of cosmetic products. In the opening lecture at SCS Formulate 1999 [Ref. 3] Dene Godfrey listed the reasons why a preservative was necessary and what makes a good preservative.

Why do we need preservatives?

Microbial contamination can cause: -

· Loss of product viscosity

· Drop in pH

· Emulsion breakdown

· Cloudiness and visible growth

· Loss of colour

· Malodour

· Skin problems

What makes a good preservative?

The ideal preservative should have the following attributes; -

· Broad spectrum activity against bacteria, yeast and moulds

· Cidal rather than static activity

· Sufficient speed of kill to satisfy accepted challenge test criteria

· Be stable and effective over the anticipated shelf life of the product

· Be safe to handle and preferably liquid

· Be safe at use concentrations

· Be effective over the pH range of the product

· Not be deactivated by other ingredients

· Be odourless and colourless

· Be readily soluble with a partition coefficient favouring water

· Be heat stable at the mixing temperature of the product

· Be cost effective

· Have approval for use in all the intended product markets

With the expiry of many preservative patents and the introduction of new preservatives being so difficult, finding synergy in mixtures of existing preservatives has been the goal of many suppliers. If it includes a material on which the patent remains this is an obvious bonus. Mixtures can have the advantage of being broad-spectrum, of reducing inventory levels and of showing a cost saving. Also it is easier to handle one liquid in reasonable quantities rather than several small weights of powders. Phenonip, a mixture of parabens in phenoxyethanol is probably the best known of all mixtures and is often copied. Recently many others have been developed that contain iodopropynyl butylcarbamate (IPBC) and these have been the subject of a number of patents.

A paper [Ref. 4] given at Preservatech USA described the development of a preservative system based on a mixture of IPBC with DMDM Hydantoin and marketed as Glydant Plus by Lonza. A paper by Spiegelman [Ref. 5] at the same conference described a broad spectrum preservative mixture of chlorphenisin with phenoxyethanol, trade named Germazide by Collaborative Laboratories. Many other mixtures have been developed and the table shows a selection of popular propriety mixtures with their principal properties. It is not exhaustive but it does illustrate the dominance of parabens and phenoxyethanol in mixed systems.

Ref 1: Kabara J.J., Orth D., Hurdle technology: a new approach to cosmetic and drug preservation. Preservatech 1998, Paris.

Ref 2:Borovian G., HACCP application in the manufacturing of drugs and personal care products. Preservatech USA – 1999.

Ref. 3: Godfrey D., A guide to preservatives, SCS formulate, UK, 1999

Ref. 4: Lutz P.J., A novel broad spectrum preservative system based on DMDM hydantoin and iodopropynyl butylcarbamate. Preservatech USA – 1999

Ref.5: Spiegelman S., Efficacy and use of chlorphenesin and phenoxyethanol based preservative systems. Preservatech USA – 1999