Mild Preservatives – Fact or Fiction?
Increasingly, there is a move within the personal care industry to seek out more “mild”, or “natural” ingredients, especially preservatives. This brief paper discusses the problems and myths associated with mild preservation.
By their very nature, preservatives are biologically active, as they are required to exert a killing effect against micro-organisms, which are living organisms. Whilst the activity of some preservatives may be highly specific, and target mostly microorganisms, as a generality, if a compound is biologically active, it has the capacity to harm other living cells. Preservatives, therefore, may cause adverse effects in human cells as a result of their inherent biological activity. Fortunately, as humans are much higher organisms, they are not likely to be killed at the concentrations required for preservation (!), but rather more mild effects such as skin irritation and sensitisation. Whilst these effects are relatively mild, they are certainly undesirable. For this reason, in the EU, all preservatives used in personal case are very carefully assessed for safety before being included on Annex VI of the Cosmetics Directive – the list of permitted preservatives. As part of the approval process, the risk of adverse reactions to the compound is assessed, and a maximum permitted concentration is assigned on the basis of providing an acceptable margin of safety. There are, however, always individuals who are more sensitive and susceptible to skin reactions, and it is not possible to totally remove the risk of an adverse response, although the vast majority of the population is at very little or no risk.
The concept of a “mild” preservative is based on the compound having a good toxicity profile, especially regarding skin irritation/sensitisation. In other words, a higher concentration of the “mild” preservative is required to elicit an adverse reaction. To illustrate this, parabens are considered to be relatively mild preservatives, whereas the isothiazolinones are not. This is reflected in the use concentrations; parabens are required at concentrations varying from 0.2 – 0.4%; isothiazolinones from 5 – 15 parts per million (0.0005 – 0.0015%). Because the parabens are relatively mild, they are not as effective as isothiazolinones and much higher concentrations are required to give the desired preservative effect. In the search for preservatives even more mild than parabens, the successful candidates for preservation will be required at still higher concentrations, as they will not be as effective on a weight for weight basis. Many of the compounds being introduced as new alternatives to traditional (and legal!) preservatives have relatively low antimicrobial activity, and will be required at concentrations in excess of 1% in many, if not most cases.
The difference in the margin of safety between an “aggressive” preservative at 0.0005% and a more “mild” preservative at 1% is very little, as the end result is a concentration high enough to exhibit biological activity – killing micro-organisms! If the search for increasingly “mild” preservatives continues, the successful candidates will be required to be used in increasingly higher concentrations in order to provide sufficient cidal activity to protect the end product. Some of the more recently introduced “natural” preservatives require concentrations a high as 5% to be effective!
So, generally speaking, “mild preservative” is a misnomer, as this simply means that higher concentrations must be used to achieve the desired protection against microbial contamination.
More about the author: Dene Godfrey has been involved with preservatives for cosmetics since 1981, from both technical and commercial angles and has a degree in chemistry. Read more from this author