Cosmetics are essential components of our grooming routine. Moisturizers, shampoos, and other products which are required to maintain quality and limit microbial growth typically consist of a mixture of numerous ingredients. Among these, preservatives are essential to maintain the safety and quality of cosmetics. Hence, the present paper discusses the types of preservatives used in cosmetics, their importance and preservative efficacy tests in relation to product safety.

Preservatives are the ingredients added to cosmetics to prevent the growth of microorganisms such as bacteria, fungi, and yeast. Such microorganisms may grow naturally in the cosmetics over time, resulting in decomposition and odors, or may have the potential of inflicting damage on the user’s skin. Preservatives help prolong the shelf life of products and hence maintain their quality thus making them safe and effective personal care products.

Significance of the Preservative Efficacy Test

The preservative efficacy test is done to determine whether a preservative incorporated in a formulated product functions to prevent the growth of the microorganisms. They are employed to simulate in-use challenges and verify the adequacy of a preservative formulation against microbial contamination. Manufactures should conduct cosmetics test to ensure that their products are up to the standard and safe for the customers.

Types of Preservatives Used in Cosmetics

There are mainly three types of preservatives used in cosmetics: natural preservatives, synthetic preservatives, and organic preservatives. The three variants have their unique characteristics and applications. The selection of any of them depends on the product formulation and subsequently its application.

Natural Preservatives

Natural preservatives are substances that are produced from natural sources such as plants, animals, and minerals. They are believed to be the best choice by philosophical minds who believe in safe and green concoctions for beauty care. Some common natural preservatives include:

• Essential oils: Naturally derived essential oils such as tea tree oil, lavender oil, and rosemary oil are characterized by their antimicrobial activity against pathogenic bacteria and fungi. Although they generally cause skin irritation, especially among the population having sensitive skin, they are used in combination with other preservatives.
• Extracts: Plant extracts such as grapefruit seed extract and rosemary extract are antimicrobial and show antioxidant properties. These natural active ingredients are often blended with other chemical preservatives to make them more potent.
• Honey and bee propolis: Honey and bee propolis are naturally antibacterial. They are widely used in the cosmetic industry, particularly in formulations designed for the population having sensitive skin.
• Alcohol: Ethanol and other alcohols are employed as chemical preservatives in cosmetic products. They act as protein denaturants and cell membrane dissolvents for the microbial content of the products. However, high concentrations can cause skin drying.

Synthetic Preservatives:

These are some of the most common and widely used preservatives, which are synthesized for the cosmetics industry due to their enhanced effectiveness and stability. The most commonly found synthetic preservatives are:

• Parabens: Methylparaben, ethylparaben, propylparaben, and butylparaben are the most common parabens used due to their broad-spectrum antimicrobial activity. They are active against bacteria, molds, and yeasts. However, parabens have shown controversy due to suspicions regarding their being endocrine disruptors.
• Phenoxyethanol: Phenoxyethanol is a glycol ether effective against a wide range of bacteria and yeast. It majorly finds use in combinations with other preservatives as it helps them become more effective.
• Formaldehyde Releasers: These include diazolidinyl urea, imidazolidinyl urea, and DMDM hydantoin and release the biocide formaldehyde over time. Although they are very effective, questions regarding their safety have been raised in their use, such as potential skin sensitization and carcinogenicity.
• Isothiazolinones: Methylisothiazolinone (MIT) and methylchloroisothiazolinone (CMIT) are potent biocides that are used in most cosmetic products. They are very active against bacteria, molds, and yeasts but can cause contact dermatitis and contact dermal allergies.

Organic Preservatives:

Organic preservatives are those that are certified for being organic and are used in products that intend to meet organic certification standards. These include:

• Benzyl Alcohol: It is an organic compound with microbicidal and antifungal properties. It shows activity over a broad range of microorganisms and is widely used in organic as well as natural cosmetic formulations.
• Potassium Sorbate: It is used as a preservative owing to the fact that it is effective against mold, yeast, and some bacteria. Sorbic acid, along with its potassium salt, is quite as widely used in natural and organic products.
• Sodium Benzoate: It is a salt of benzoic acid and is effective against both yeast and bacteria. This preservative is often used in combination with other preservatives to broaden its action.

Efficacy Determination of Preservatives in Cosmetics:

Determination of preservative efficacy is done to demonstrate the capability of the products to protect cosmetic articles against microbial contamination. Proof of its efficacy in cosmetic products is required for the safety of the general public. The test methods include:

Challenge Test:

The term challenge test is popularly recognized as a preservative efficacy test. The challenge test is the process of deliberate contamination of the cosmetic formulation with a cocktail of microorganisms and determination of the microbial load over time. The most popular method in a challenge test is the ISO 11930, as it determines the product’s antimicrobial protection.

Microbial Enumeration Test:

Microbial enumeration tests are the tests to quantify the live microbes in the cosmetics during its shelf life. The most commonly used methods include the plate count test, membrane filtration, and most probable number.

Antimicrobial Susceptibility Tests:

Antimicrobial susceptibility testing is done to assess the activity of preservatives for specific microorganisms. The commonly used methods for determining antimicrobial susceptibility are disk diffusion, broth dilution, and agar dilution. These tests determine the Minimum Inhibitory Concentration (MIC) of the preservative for target microorganisms.

Stability Testing:

Stability testing is performed to assess the physical, chemical, and microbiological stability of a cosmetic preparation under diverse environmental conditions. It is performed so that preservative efficacy could be ensured over the shelf life. It includes the following studies: accelerated aging studies, real-time aging studies, and compatibility studies with packing materials.

Testing Methods for Cosmetics Available at MIS:

Preservatives are included in cosmetics to preserve it and save the consumer from the fatal effects of microbial contaminants. Several international standards and regulatory bodies govern the use of preservatives in cosmetics. Each country and region has its standards and regulations. Some of the cosmetics tests carried out at MIS include:

ISO 16212 – Enumeration of yeast and mold

ISO 21149 – Enumeration and detection of aerobic mesophilic bacteria

ISO 21322 – Testing of impregnated or coated wipes and masks

ISO 14730 – Antimicrobial preservative efficacy testing and guidance on determining discard date

PCPC M-5 – Preservation Testing of Nonwoven Substrate Personal Care Products

PCPC M-6 – Preservation Testing of Atypical Personal Care Products

PCPC M-7 – Preservation Testing of Water-Miscible Personal Care Products

At Microbe Investigations Switzerland, we provide detailed testing services to evaluate the efficacy and safety of preservatives used in cosmetic products. Our expert microbiologists utilize cutting-edge techniques to ensure that your cosmetics meet regulatory standards and remain safe for consumer use. By testing a wide range of preservatives, we help you maintain the quality and longevity of your products, protecting both your brand and your customers.

To learn more about our preservative testing services or to schedule a consultation, please contact our specialists today.