Stability of cosmetic products: shelf life or PAO?


IDEA Microbio, the IDEA TESTS GROUP laboratory dedicated to microbiology, offers, with more than 25 years experience, all the services necessary to provide stability assessment of a cosmetic product required by the Cosmetics Regulation EU 1223/2009

Cosmetic products must be safe for human health and the Regulation requires that a Cosmetic Product Safety Report (CPSR) is set up that includes a section on the stability. The aim is to determine the shelf life of finished products or the Period After Opening (PAO).

The reasons for stability assessment of cosmetics are:

  • to maintain the intended quality and specifications (related to the aspect of the product but also to the skin tolerance)
  • to determine whether a shelf life or a PAO is required, and, if needed, to calculate the PAO value
  • to assess the microbial stability of the product and hence to ensure the safety for the consumers
  • and, finally, to preserve the image and the reputation of the companies

First the date of minimum durability or shelf life of the unopened product must be determined. Because of the very wide variety of cosmetics, there is no standard overall protocol and the study design is determined after consideration of the normal foreseeable conditions of storage and use of the product. In most cases accelerated stability studies are performed (specific temperature, hygrometry, light and duration conditions) over at least 5 months. During that period of time, at regular intervals, product samples are evaluated. The evaluated parameters vary depending on the product but generally include criteria such as colour, odour, appearance, pH, viscosity, density, weight, microbiology.

Particular attention should be also paid to the compatibility of the product with its packaging.

If any of these parameters is changing, this could be an indication of a modification of the quality of the product and hence of its safety.

According to the EU Regulation, if the shelf life is lower than 30 month, an expiration date must be indicated onto the packaging.

Conversely, if the shelf life is at least 30 months, no indication of expiration date is required on the packaging, but a PAO is mandatory.

The PAO correspond to the period during which the product is stable after opening and can be used without any risk for the human health. Therefore, it includes de facto an assessment of the stability of the product after opening toward the risk of microbial contamination.

Ideally, after this period of time, a microbial control of the product and new preservative efficacy test (challenge test) should be performed.

The same criteria as those studied for the shelf life will be evaluated but after simulating a real use of the product over a period of 3 months (unless otherwise specified by the manufacturer).

The PAO can also be evaluated theoretically on the basis of the same parameters of the product that are used for the microbial risk assessment (i.e. composition, packaging, target population, application area, frequency of use, special storage conditions, etc.)

Hence, the PAO determination also takes into account the type of product and its claim. Particularly, a reduced PAO should be required for cosmetics to be used on sensitive body parts (around the eyes, on mucous membranes, on damaged skin) and on specific populations (children under 3 years, elderly people, people with compromised immune responses).

The PAO is indicated onto the packaging with a symbol representing an open cream jar accompanied by an indication of the period of time shown as a number.

Stability studies and PAO determination are also available at IDEA Lab and whatever your project or your product, they are a critical element of the CPSR that should be evaluated as soon as possible after validation of the formulation.

For more information, please contact Frédéric NUNZI:
Head of IDEA Lab, Doctor in Cell Biology and Microbiology / Eurotox Expert (Regulatory and in vitro Toxicology)

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