The Period After Opening is a key element of cosmetic safety information. It tells consumers how long they can safely use a cosmetic product after opening its primary packaging for the first time. Unlike a fixed expiry date, which applies whether the product is opened or not, the PAO countdown starts at the moment the product comes into contact with air and potential contaminants.
The PAO helps consumers understand how long the product maintains its safety, stability, and performance during real-life use.
Visual Representation and PAO Marking on Packaging
Cosmetic packaging displays the Period After Opening using the recognizable open jar symbol. This symbol resembles an opened container and appears on the label when a product requires PAO information.
Inside or next to the symbol, manufacturers indicate a number followed by the letter “M,” such as 6M, 12M, or 24M. The letter “M” stands for months. For example, a 12M symbol means the product remains safe and effective for 12 months after first opening.
In the European Union and many other markets, PAO marking is mandatory for cosmetic products with a minimum durability of more than 30 months.
The Scientific Basis of PAO and Cosmetic Stability
The PAO directly reflects the microbiological and physical stability of a cosmetic product after opening. Once the protective seal breaks, the product faces several risk factors that can affect safety and quality.
Microbial contamination occurs when microorganisms enter the product from air exposure, fingers, or applicators. Over time, this contamination can overwhelm the preservative system, reduce product quality, and increase the risk of consumer infection. The Period After Opening defines the period during which the product remains microbiologically safe under normal conditions of use.
Physical and chemical degradation also influence PAO determination. Exposure to oxygen and light can trigger oxidation of active ingredients, fragrances, and oils. These changes may alter the product’s color, odor, texture, and effectiveness. The PAO reflects the point at which such degradation may compromise product performance.
Difference Between PAO and Expiry Date
Consumers often confuse the PAO with the expiry date, but these two markings serve different purposes and apply to different product lifecycles.
A fixed expiry date, also known as the “Best Before End” date, applies to cosmetic products with a shelf life of 30 months or less. This date indicates when the product should no longer be used, regardless of whether it has been opened.
The Period After Opening applies to products with a shelf life longer than 30 months. Once the consumer opens the product, the PAO becomes the controlling safety reference. Even if the product is newly manufactured, the user must stop using it after the indicated Period After Opening period, such as 6 or 12 months after opening.
Why PAO Is Essential for Consumer Safety
The Period After Opening serves as a practical consumer safety guideline. It protects users from risks linked to microbial growth, ingredient degradation, and reduced preservative effectiveness after opening. By following the PAO, consumers help ensure that cosmetic products remain safe, stable, and effective throughout their intended period of use.
PAO or date of minimum durability: which one applies
Cosmetic labels carry one of two durability indications, and the choice between them is determined by the product’s shelf life rather than by preference.
Where the minimum durability of the product exceeds 30 months, the label must show the Period After Opening — the open-jar symbol followed by a figure in months, such as 12M. This tells the consumer how long the product stays safe once it has been opened and exposed to air, skin and applicators.
Where minimum durability is 30 months or less, the PAO is not used. Instead the label carries a date of minimum durability, expressed as “best used before the end of” followed by the date, or the hourglass symbol alongside it. Using both indications on the same product is a common labelling error — they answer different questions and only one of them applies.
How the PAO figure is determined
The number inside the open-jar symbol is not chosen for marketing reasons and cannot simply be copied from a similar product. It must be justified by evidence held in the Product Information File, and the safety assessor confirms it as part of the safety assessment.
Three inputs normally support the figure. Stability testing shows that the formulation remains physically and chemically stable over the claimed period. Preservative efficacy testing under ISO 11930 demonstrates that the preservative system continues to control microbial growth after repeated opening and use. Packaging compatibility data confirms that the container itself protects the product and does not interact with it.
Packaging format matters more than brands often expect. The same formulation in an airless pump and in an open jar will not necessarily justify the same PAO, because the jar exposes the product to far more contamination during normal use. Where a product is sold in several formats, the evidence has to support each one.
Products that do not need a PAO
The PAO is not universal. It may be omitted where the concept is meaningless for the product in question:
- Single-use products, such as sachets and single-application ampoules, which are not stored after opening
- Products in packaging that prevents contact with the outside environment, such as sealed pressurised aerosols
- Products where there is no meaningful risk of deterioration after opening, which in practice covers many anhydrous and high-alcohol formulations
Where the PAO is omitted on this basis, the reasoning belongs in the Product Information File. An authority reviewing the file will expect to see why the omission is justified, and “the product does not deteriorate” is only persuasive when the stability and packaging data support it.
Frequently asked questions
Can I choose 12M just because competitors use it?
No. The figure must be supported by stability, preservative efficacy and packaging data in your own Product Information File. Copying a competitor’s PAO gives you a number you cannot defend if an authority asks for the evidence behind it.
What happens if the PAO is shorter than the shelf life?
That is normal and expected. Shelf life describes the unopened product; the PAO describes it after opening, when it is exposed to air and skin contact. A product can be stable for 36 months unopened and safe for 6 months once opened.
Does the PAO symbol have a minimum size?
The Regulation does not prescribe exact dimensions, but all mandatory label information must be indelible, easily legible and clearly visible. A symbol too small to read in normal conditions does not meet that standard.
Do anhydrous products need a PAO?
Often not, because there is no realistic risk of microbial deterioration after opening. The exemption still has to be justified in the Product Information File rather than assumed, and oxidative stability of oils should be considered separately.
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