How is the expiry date of a cosmetic product determined?

Cosmetics: What does the expiration date signify?

Just like food, cosmetics can have harmful effects on the body if they are used beyond a certain period, ranging from simple redness to eye irritation or swelling. That's why it's important to adhere to a certain usage timeframe. There are two types of dates that can be found on a cosmetic product.

The Minimum Durability Date (MDD) or Best Before End Date (BBE) : This date is found on cosmetics with a lifespan of less than 30 months and is preceded by the phrase "to be used before" or "best before" in English. It indicates the date until which the product can be used without risk. The MDD is represented by an hourglass-shaped pictogram.
The Period After Opening (PAO): For cosmetics with a usage duration exceeding 30 months, it is more commonly a period of use after opening that is indicated. This specifies the length of time during which the product can be used from the moment it has been opened. This date is symbolised by an open cream jar, inside which there is a number and the letter M. For instance, if inside the cream jar there is the notation "6M", this means that the product can be used up to 6 months after its opening.

Even though each product is unique, there is an average usage duration after opening that is specific to each type of skincare product. These Period After Opening (PAO) are indicated in the table below.

Cosmetics	Average Period After Opening
Facial care (creams, serums, eye contours...)	8 months for products contained in jars and 12 months for those in pump bottles
Body Care	Between 9 and 12 months
Makeup Removers and Micellar Waters	Approximately 12 months
Shampoos and Shower Gels	Between 24 and 36 months
Sun Care	A season
Eyeliners and Mascaras	Between 1 and 3 months
Powder-based treatments (eyeshadows, blushes...)	Between 12 and 18 months

Les périodes d'utilisation moyennes après ouverture des cosmétiques.

Note : If you can't remember when you opened a product, you can examine its organoleptic properties to get an idea of its condition. A change in smell, texture, or colour indicates that it's time to part with it.

Pictogrammes indiquant respectivement la date de durabilité minimale (DDM) et la période après ouverture (PAO) — Pictograms indicating respectively the minimum durability date (MDD) and the period after opening (PAO).
Source: Regulation (EC) No 1223/2009 of the European Parliament and the Council.

How are the minimum durability date and the period after opening determined?

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).