How is the expiry date of a cosmetic product defined?

The determination of the minimum durability date (MDD) and the period after opening (PAO) is carried out by the formulator following the development of the product. For this, several criteria are taken into account, allowing for the calculation of a date.

• Microbiology.

  The Challenge Test, conducted in accordance with the European Pharmacopoeia, is the primary criterion to consider when establishing an expiry date. This mandatory test to be carried out before a cosmetic product is launched on the market, allows for the control of the product's sensitivity to bacterial contamination. For the product to successfully pass the test, its preservation system must be sufficiently effective to reduce the level of microorganisms to the microbial limits authorised and predefined by Cosmetic Regulation. The results obtained by the cosmetic during the Challenge Test partly determine its Best Before Date (BBD) and Period After Opening (PAO).

• The composition and pH of the product.

  The percentage of water contained in the cosmetic also plays a significant role in determining the Best Before Date (BBD) and Period After Opening (PAO). Indeed, the presence of water in a product facilitates the proliferation of microorganisms, such as bacteria, yeasts, and moulds, which not only degrade the quality of the product but can also pose health risks to users. Thus, a product containing little or no water will tend to have a longer BBD and PAO.

  The pH of the skincare product can also influence the risks of bacterial contamination and therefore determine the Period After Opening (PAO). Indeed, most microorganisms preferentially thrive in a neutral environment. A more acidic or more basic pH level thus creates an unfavourable environment for the majority of pathogens.

• The product packaging.

  The packaging of the cosmetic product is also a factor to consider when assessing its Best Before Date (BBD) and Period After Opening (PAO). Thus, products in jars generally have a lower PAO than others as they are more susceptible to bacterial proliferation due to contact with fingers and air. Cosmetics preserved with a pump bottle, on the other hand, are generally more stable over time.

• The function and usage instructions of the product.

  Depending on the product's mode of use, for example, whether it is rinse-off or not, and the targeted consumers (children, pregnant women...), the Period After Opening (PAO) and the Expiry Date (DDL) can slightly vary. Rinse-off products, by definition, stay in contact with the user's skin for a shorter period, often have a longer PAO. On the other hand, those intended for pregnant women or children, who are more at risk populations, tend to have shorter usage durations.

• The existence of specific risks.

  Finally, the unique characteristics of each cosmetic product are studied. If it is likely to be mixed with others, as can be the case with stick-form products, its Period After Opening (PAO) should be relatively short. The same applies to portable products, such as sun creams or lip balms, which may be exposed to significant temperature variations.

Note : Consumer behaviour can influence the period after opening. Using products without washing hands beforehand, not closing them properly, or storing them in very hot places can accelerate the growth of microorganisms and reduce the PAO (Period After Opening).