All cosmetic formulations require preservatives to protect them frommicroorganisms, even though they are potentially sensitising compounds. Logically, the more preservatives in the product, the more likely the formula will cause a sensitivity effect.

Why use presevatives?

Because of the potential infection of cosmetic ingredients by microorganisms, preservatives must be added to cosmetic formulations. Contamination of formulations can lead to the separation of emulsions, product discolouration, the formation of gasses and odours, as well as the infection of the skin of the user. 

Customer usage and storage of cosmetics and skin care is often lax, care is not taken in replacing lids and fingers are often used to remove the cream or foundation from the container. Storage could be the bottom of a handbag, the glovebox of the car or in a damp bathroom cupboard, these habits create a potential breeding ground for bacteria of all kinds. A variety of infections including yeasts, fungi and bacteria, including pseudomonas, staphylococci and streptococcus have been identified in cosmetic preparations.

In addition many problems with preservative failure in cosmetics have been related to expiry of usable shelf life and extreme temperature variation during storage.

The presence of preservatives in cosmetic products is obviously necessary, however, many preservatives have the potential to cause allergic reactions on sensitive skins.

At the present time, parabens, (methylparaben, ethylparaben and butylparaben etc) are the most commonly found cosmetic preservatives. Given the prevalence of parabens, there are relatively few allergic reactions (typically 3.6% of all adverse reactions) to these substances, and almost all problems occur on lipid dry, cracked or inflamed skins.

Quaternium-15 is a preservative found in many cosmetics. It is a water soluble anti-microbal agent that has proven active against bacteria, but less active against yeasts.

It was found to be responsible for over 12% of allergic reactions in the American study.

It is a formaldehyde releaser, and may be a major cause of dermatitis from preservatives. People who may be allergic to formaldehyde, can potentially have problems with this ingredient. It has also recently been found that quaternium-15 can react in the body with other chemicals to produce nitrosamines. (known carcinogens)

However, it is not known whether enough Q-15 can be absorbed through the skin for the carcinogen producing action to occur.

It is the knowledge that Q-15 can react with other chemicals that leads the therapist to the understanding of why it is not good practice to mix brands of cosmetics, or encourage the client to do so.

Cosmetic houses know that the substances within their line are compatible, but generally do not know of the compatibility of other skin care lines.

Formaldehyde is a inexpensive and effective preservative that is widely used in cosmetics as a disinfectant, germicide, fungicide and de-foamer. It has been estimated that between 4-8 % of the general population may be sensitized to this popular preservative.

More recently, serious questions about the safety of this substance have been raised, to the point that it is prohibited in cosmetics in both Japan and Sweden.

Individuals who are allergic to formaldehyde may also have adversity with Imadazolidinyl urea and diazolidinyl urea, as these substances can also release formaldehyde.

Persons allergic to formaldehyde may also have problems with 2-bromo-2-nitropropane-1-3 (more commonly known by the brand Bronopol) or DMDM hydratoin, 5-bromo-5-nitro-1,3 dioxane (also known as Bromidox), and tris (hydromethyl) nitromethane.

Sorbic acid is a common cosmetic preservative that occasionally causes allergic reactions, although it was found to be responsible for only 1.1% of allergic reactions in the study. People allergic to sorbic acid may also react to a related ingredient called potassium sorbate.

Two newer cosmetic preservatives that have been used in European products for some time are Methyl-chloroisthiazolinone and Methylisothiazolinone. (Kathon CG)

These ingredients have been responsible for numerous allergic reactions, however, when used in lower concentrations they have been found to cause fewer problems.

The newest preservative system found in cosmetics, Euxyl K 400, is a combination of Phenoxyethanol and Methyldibromoglutaronitrile. There has been some documented cases of allergic contact dermatitis related to this substance, but at this time there is insufficient data to determine significant problems.

Listed below are the most common preservatives you may encounter in cosmetic products. Antioxidants, although often listed under a separate title are also preservatives that help protect the formulation from deterioration from contact with oxygen.

Compounds listed in italics are known allergens or sensitisers.

Many cosmetic formulations that contain substances designed to penetrate the skin more rapidly than natural ingredients (such as water) are also potential sensitisers. They are generally part of the emollient or surfactant portion of the formulation.

Penetration enhancing substances have the ability to significantly alter the lipid barrier function of the stratum corneum, and should be considered a potential source of irritation. The use penetration enhancing substances to assist in the delivery of drugs in to the skin is accepted in prescription medications, as the contact time of the product is strictly controlled.

In the case of cosmetic formulations, the uncontrolled and prolonged use of products containing these substances may lead to allergic reactions on individuals with susceptible skins. In the American study, over 10% of the allergic reactions studied where due to penetration enhanced emollients.

Although penetration enhancing substances help the delivery of active ingredients into the skin, other irritating ingredients in the formulation such as fragrances, surfactants and preservatives are also absorbed more readily. Paradoxically, nature designed the lipid barrier of the stratum corneum to repel the potential aggression of such chemicals.

Below are some of the chemical agents reported to enhance the penetration of specific chemicals in to the stratum corneum.

Colouring agents

Even high profile and expensive domestic retail products can contain coal tar based colourings. The belief that price or labelling stating hypoallergenic will ensure a higher quality or refinement of ingredients is no guarantee in the case in colour cosmetics.

With the advent of product composition disclosure on packaging, the task of finding out what colourings are present is now far easier.

Colours used in food, drugs and cosmetics are classified by type with a letter code (F,D,C) which indicates the use for which it is approved. These letters will precede the number and description of the colour. An example is FD&C yellow No5.

When the letters FD&C precede a colour it means the colour can be used in food, drugs or cosmetics.

D&C signify that it can only be used in drugs and cosmetics, and not in food.

The code Ext D& C before a colour means that it is certified for use in drugs and cosmetics for external use only, and may not be used on the lips or mucous membranes.

No coal tar based colours are approved for use around the eyes. In fact, no colour additive should be applied around the area of the eye unless specifically approved for that purpose. There are too many colours to individually list, and many colours will have no adverse effects when used correctly. There are however, a number of colours used in food and cosmetics that have been the focus of legal action in the US over the past ten years.

The suitability of FD & C Red No3 and D & C colours Red 8, Red 9, Red 19, Red 33, Red 36 and Orange 17, have all been challenged by the US Public Citizens Health Research Group. Successful legal action has prevented some of these colours being permanently listed as safe by the US Food and Drug Administration.

Care must be taken when applying cosmetics that may contain coal tar derived colours, as these products are unsuitable for use on the lips or eye lids.

Consider the habit of many women to use make up on areas of the face that it was not originally intended for, examples of this are using lipsticks as a blushers, blushers as eye-shadows and powdered eye-shadows wetted for use as eyeliners on the inside of the lower lid. Long term misuse of products in this manner increase the risk of sensitivity and allergy reactions.

Be vigilant and take care when next you buy your colour cosmetics (makeup).