Preservatives: The Villain in the Bottle

Preservatives are certainly the villain in the bottle when examining recommendations from consumer watchdog groups, such as the Environmental Working Group, and internet product evaluation apps, such as Yuka. Why are preservatives so controversial? The role of preservatives is to kill bacteria, yeast, fungi, and mold. The typical unpreserved cosmetic will last about 1 week after opening before contamination occurs. Most consumers would not wish to purchase cosmetics weekly as they do for milk products. They are also unlikely to enjoy refrigerating their cosmetics, like meat products, only to have them spoil in a matter of weeks. Any cosmetic that contains water is especially prone to contamination. Water-free products, such as petroleum jelly, do not require preservation and are not loaded with preservatives. Most cosmetics contain water, however.

MORE AESTHETICS

It is hard to develop a cosmetically elegant preservative; however, there are ways to minimize the need for higher preservative concentrations. One method for preservative reduction is to carefully design the product container. Open-mouthed jars, which are the least expensive form of packaging, allow consumers to put their fingers in the jar, introducing contamination. A 1-way bag nozzle delivery system is the best but the most expensive. Here, the product is encased in a sealed bag, and once the top is pressed, a metered amount of product exits through a 1-way nozzle, prohibiting air from entering the bag. This 1-way system does not expose the product to the environment, oxygen, or consumer manipulation. Packaging is the first step to lowering preservative concentrations.

A second technique for enhancing preservation is the use of substances that function as preservatives but are not classified as preservatives. For example, adding ethanol to a formulation will increase its shelf life, functioning as a preservative, but ethanol is damaging to the stratum corneum as a potent solvent and may not be appropriate in products for diseased skin or skin with a damaged barrier. Benzyl alcohol is also used for this purpose. Some plant-derived essential oils can be used for product preservation, thus avoiding classification as preservatives. Examples include rosemary (Rosmarinus officinalis), lavender (Lavandula officinalis), tea tree (Melaleuca alternifolia), salvia (Salvia officinalis), and eucalyptus (Eucalyptus globulus), to name a few. There are several challenges with using plant-derived essential oils as preservatives. First, the plant materials have a smell, which may or may not be desirable. Sometimes lower concentrations can be used in conjunction with more traditional preservatives, but this may defeat the purpose. Finally, if all products used plant materials for preservation, sustainability would be an issue with depletion of the environment.

A third preservation technique is to formulate at an acidic pH. There are limitations here also, as highly acidic products are not skin-compatible. Lowering the pH can reduce preservative concentration, but it does not eliminate it.

We are then back to the fact that preservatives are a necessary villain in most topical cosmetics. Kathon CG, also known as methylchloroisothiazolinone and methylisothiazolinone, was introduced to reduce the need to use parabens. After it entered the marketplace, it was found to be a source of allergic contact dermatitis. Now, it is no longer allowed in leave-on formulations in the European Union. Parabens, usually used in combination as methylparaben, ethylparaben, propylparaben, and butylparaben, can be endocrine disruptors because they mimic estrogen, but remain the safest preservatives in the marketplace today. They are commonly used in combination with phenoxyethanol, which is sometimes identified as a fragrance because it smells like roses.

What is the take-home message regarding topical application of preservative-containing cosmetics? I would recommend the following suggestions:

• Wash off all skin care products when not needed on the skin.
• Remove sunscreen when no longer in the sun.
• Wash all cosmetics off prior to bedtime.
• Choose cosmetic products with low contamination potential due to packaging.
• Do not eat skin care products.

Zoe Diana Draelos, MD, is a clinical faculty member in the Department of Dermatology at Duke University School of Medicine in Durham, North Carolina; president of Dermatology Consulting Services in High Point, North Carolina; and Dermatology Times’ editor in chief emeritus.

MORE FROM DRAELOS