John Found Dip. Chem., C. Chem., MRACI, MAICD
What are Preservatives in Cosmetics?
Preservation is an essential part of our everyday life and it allows us to ensure products are safe and effective. We have all seen the effects that the growth of bacteria and mould can have on unpreserved liquid and cream products. Micro-organisms need at least three basic parameters to flourish:
- Correct temperature
If we remove one of those parameters, we can successfully inhibit microbial growth. Products with no water content, for example, do not need preservation. Similarly frozen products will last a very long time un-preserved
How Preservatives Work
Preservation for water-based products can take many forms. They can range from typical chemical actives to simply chilling or heating, adjusting the pH or even adding salt. Unfortunately, chemical active preservatives must work by either making life support for micro-organisms difficult (bacteriostatic) or by being cytotoxic (bactericidal). Essentially a good preservative system must be poisonous to bacterial and fungal cells. Fortunately, micro-organisms are much more susceptible to death or inactivity from chemical attack than humans.
What Makes A Good Preservative System?
It’s important to remember that the purpose of preservatives is not to act as a disinfectant. Bacteria laden creams and lotions may inactivate preservative systems by simply overwhelming the chemicals that are designed to control them. Preservative systems are designed to knock down any low bacteria numbers introduced by the end user. Effective preservation is quite complex because it depends on many parameters. For example, we may have an acne cream which naturally has a pH of about 3, common spoilage organisms very rarely flourish below a pH of about 4 so our product can be technically “preservative free” because we don’t have to add preservative chemicals .
A solution with few bacterial nutrients may require minimal preservation whereas those with large amounts of nutrients will need much more robust systems. In creams and lotions we need to consider the relative solubility of preservatives in the oil and water fractions and the presence of ingredients that may inactivate a chosen preservative such as ethoxylated surfactants.
Modern v Historical Preservation
Modern preservation techniques rely on a combination of chemicals as some ingredients are more active against certain organisms than others. Truly broad-spectrum single ingredient preservatives are rare.
Historically preservatives were selected from highly toxic chemicals that were used in low concentrations. They include arsenic, mercury, formaldehyde, and chloroform and were widely used many decades ago. The development of regulatory bodies around the world has ensured preservatives that carried a significant risk to human health were outlawed. To gain perspective on what is safe and what is not safe we need to have some understanding of toxicology.
Nature embodies decay and the primary pathway is by microbial action, without microorganisms our planet could not survive. Naturally occurring preservatives are therefore rare and often require chemical concentration and/or extraction to be effective. Many products and raw material suppliers tout the use of “natural preservatives” and although well intentioned some are simply not effective enough to be viable. A few of the natural combinations can be useful for systems with low nutrient levels but because of relatively low efficacy compared to their chemically active cousins they frequently fail. Preservative efficacy testing is strongly advised when venturing into natural preservation.
The toxicological pathway has a lot to do with how safe a product is, for example the human intravenous pathway is many orders of magnitude more sensitive to toxins than an oral pathway which, in turn, is many orders of magnitude more sensitive than applying them to the skin. This is simply because the amount of a toxin absorbed trans dermally needs to be very large for most chemicals compared to direct injection. Regulators take this into account when making determinations about the suitability of preservatives in products for human use.
Therefore, you can look at a Safety Data Sheet for a compound and find all sorts of alarming warnings and precautions but find the same chemical in your skin care products which has no such warnings. This does not mean that your shampoo or moisturiser is unsafe, it merely means that it is safe in the correct concentration for that application.
What’s Good and What’s Bad
Advertising would have you believe that the health effects of preservatives vary widely and are generally undesirable. Social media would have you believe that your life is at risk by using products with notorious preservatives. Neither of these positions are technically correct and unfortunately internet based false information is widespread especially for personal care ingredients. There has been a general move away from good preservative systems such as mixed hydroxybenzoates largely because of misinformation.
The modern trend is to utilise preservative systems that are used in food products, remembering the many orders of magnitude of safety that it implies. Ingredients generally accepted as being “good” include:
- Sodium or potassium salts of sorbic acid, salicylic acid and benzoic acid.
- Dehydroacetic acid
These compounds have found recent favour and have excellent safety profiles.
Those moving out of favour recently and considered “bad” are the formaldehyde donors, these additives are not toxic to bacteria in their own right but gradually break down to form small amounts of formaldehyde which is cytotoxic. Even though the amount of formaldehyde is exceedingly small and considered safe by most regulators for its purpose, its potentially carcinogenic profile in large regular doses would suggest that it is not the preferred ingredient. There are at least 42 of these compounds and they have almost unpronounceable names such as:
- Imidazolidinyl urea
- Diazolidinyl urea
- DMDM hydantoin or sodium hydroxymethyglycinate
Formulators need consider many attributes such as formulation type, pH, water content, potential bioburden, packaging type, indications for use, customer preference and many other parameters to ensure that the final product is safe and effective. At Wild Child, we are full-service contract cosmetic manufacturers that can support you at every stage, from product development to manufacturing and regulatory compliance. Contact us today if you need more assistance.