PAO in Cosmetics: Period After Opening Explained
The PAO (Period After Opening) is more than just a pictogram on packaging.
It is a key regulatory indicator, based on a comprehensive toxicological assessment and binding on the manufacturer.
As experts in cosmetic regulations, Toxi Plan explains everything you need to know about cosmetic PAOs ⬇
A definition to start with: what is PAO?
The PAO (Period After Opening) is the period during which a cosmetic product can be safely used after its first opening, provided it is stored under normal conditions.
It is represented by the following symbol: (see photo below)
Example: 12M, 6M, 24M
This means that the product remains safe for 6, 12, or 24 months after opening, not from the date of manufacture.
PAO ≠ MDD
It is essential not to confuse the two:
Label | Meaning |
MDD (Minimum Durability Date)) | Before opening |
PAO (Period After Opening) | After opening |
If the MDD exceeds 30 months, the MDD becomes optional and the PAO becomes mandatory.
This is the case for most cosmetic products.
6-month cosmetic PAO, visible in the photo above.
Here is a 12-month cosmetic PAO (Period After Opening) which is visible in the photo above.
How is PAO defined?
The PAO (Period After Application) is never chosen arbitrarily. It is based on a scientific risk assessment, taking into account:
- the formula
- the preservative system
- the packaging
- the method of use
- the application area
- the consumer profile
What tests are performed?
🔬 1. The challenge test (preservation effectiveness test)
The cosmetic challenge test, also known as the preservation efficacy test, is the central test for evaluating the microbiological safety of a product. In practice, laboratories intentionally inoculate the product with microorganisms and then monitor their evolution over time. This allows them to verify the preservative system’s ability to control contamination and ensure product safety throughout its use.
Microorganisms tested (according to ISO 11930):
- Staphylococcus aureus
- Pseudomonas aeruginosa
- Candida albicans
- Aspergillus brasiliensis
- Escherichia coli
The objective is to verify that the preservative system effectively controls contamination.
🧪 2. Stability tests
Cosmetic stability tests assess how a product evolves over time by analyzing its physicochemical stability, as well as its sensory characteristics such as:
- odor
- color and texture
- pH
- and compatibility between the formula and the packaging.
To obtain reliable results, laboratories conduct these tests at room temperature, under accelerated conditions, and, in some cases, under real-world usage conditions.
🧴 3. The influence of packaging
Cosmetic packaging plays a major role in defining the product’s shelf life after opening (PAO), as it directly influences the risk of product contamination.
For example, an open jar exposes the formula more to microorganisms, while systems like pump bottles, airless pumps, or tubes limit this risk.
👉🏼 Thus, even with an identical formula, two products can have different shelf lives after opening, solely due to their packaging.
What is the role of the toxicologist?
The cosmetic toxicologist plays a key role in defining the PAO (Period After Opening) for cosmetics, as they analyze all available data to assess the level of risk to the consumer. They are involved at every stage, interpreting test results, taking into account usage conditions, and ensuring that the period after opening is based on sound scientific justification. Here are their three main roles:
✅ Analyze all data
- Challenge test
- Stability
- Raw material data
- History of similar formulas
✅ Assess the actual risk to the consumer
This takes into account:
- frequency of use
- application area (face, eyes, mucous membranes, etc.)
- target population (adults, children, sensitive skin)
- potential level of contamination after opening
✅ Determine the justified PAO (Period After Opening)
The PAO corresponds to the period during which the product remains safe under normal conditions of use.
This justification is included in the Cosmetic Product Safety Report (CPSR), a mandatory document according to European Cosmetic Regulation 1223/2009.
What PAO is not:
This is not a marketing estimate.
❌ This is not a “standard” duration (12M by default).
❌ This is not simply a consequence of the challenge test.
PAO is a scientifically sound decision, involving food safety, regulatory compliance and the manufacturer’s legal responsibility.
Why is this a strategic issue for manufacturers?
A poorly defined cosmetic PAO (Period After Application) can have significant consequences, as it exposes the manufacturer to regulatory non-compliance and can create inconsistencies in the product file. Furthermore, it can call into question the validity of the CPSR (Product Safety Record) and increase the risk to the consumer. Consequently, authorities or auditors may issue observations or even reject the product during an inspection.
The PAO (Period After Opening) for cosmetics refers to the period during which a product remains safe after opening; it therefore directly guarantees consumer safety. To define it, manufacturers rely on both rigorous testing (such as stability tests and challenge tests) and genuine toxicological expertise. Furthermore, this period depends heavily on the formula used and the packaging, which can influence the risk of contamination.
Consequently, the toxicologist must scientifically justify the PAO in the CPSR (Product Safety Report), in accordance with regulatory requirements.
Disclaimer:
The information provided in this article is for informational and educational purposes only. It does not constitute legal advice nor a personalized regulatory consultation. Despite the care taken in drafting this article and verifying its sources, regulations evolve regularly and may be subject to differing interpretations depending on the specific context of each company, product, or market.
Toxi Plan®, its directors, and its employees shall not be held liable for any use made of the information contained in this article without further analysis tailored to a specific situation. Any regulatory or strategic decision should be based on a specific assessment carried out by a qualified professional, with due regard to the applicable regulations, including any provisions or regulatory practices entering into force after the date of publication.