A preservative is a natural or synthetic ingredient that is added to a cosmetic product to prevent microbial contamination (bacteria, mold, yeast, etc.), as well as to prevent degradation by environmental factors such as heat, light, and air. Cosmetics have a high potential for microbial contamination and growth. The most susceptible products are creams and lotions that are packaged in jars, opened frequently, and applied to the skin with the fingers. Inadvertent contamination may also occur after the use of makeup brushes around the eyes or other parts of the face that touch the skin and the cosmetic repeatedly. Each use increases the chance for contamination. Furthermore, contamination may occur if the consumer leaves a product container open for an extended period of time.
Another major cause of product contamination is storage conditions. Since the majority of products are stored at room temperature, the warm temperature can stimulate the growth of microorganisms. Plus, the ingredients used in cosmetic formulations, such as water, oils, peptides, and carbohydrates, create the perfect environment for microorganism growth. Microbial contamination can lead to many problems, such as skin irritation and infections.To avoid these problems, a strong yet non-irritating preservative must be added to the formulation of a product. Examples of commonly used preservatives in skin care include phenoxyethanol, chlorphenesin, sodium benzoate, and parabens.