Cosmetic product stability is essential to ensure safety, performance, and regulatory compliance. In this context, two concepts often raise questions: PAO in cosmetics and the expiry date (also referred to as the minimum durability date).
Although both indicators relate to product stability, they are not equivalent and cannot be used interchangeably. Each applies to a different stage of the cosmetic product lifecycle and must be supported by specific technical studies.
Understanding these differences is key for Quality, Microbiology, and Regulatory Affairs teams, as correct determination directly impacts consumer safety and legal compliance.
What Is PAO In Cosmetics And What Does It Really Indicate
PAO in cosmetics (Period After Opening) indicates the period during which a cosmetic product can be used safely after it has been opened for the first time.
It is shown using the open-jar symbol, followed by a number and the letter “M” (for example, 12M).
Unlike the expiry date, PAO does not assess the product in a closed state. It focuses on real-use conditions once the product has been exposed to external factors.
When Is PAO Mandatory To Declare (≥ 30 Months)
PAO must be declared when the product’s minimum durability exceeds 30 months. In these cases, it is not mandatory to indicate a specific expiry date. Instead, the label must state the safe period of use after opening.
This requirement is established under Regulation (EC) No 1223/2009 on cosmetic products.
Factors That Can Shorten PAO (Packaging, Use, Contamination)
PAO can be reduced by several factors, including:
- Air exposure and oxidation
- Repeated manual contact
- Applicator type
- Secondary contamination
- Temperature variations
- Light exposure
Jar packaging typically presents a higher contamination risk than airless systems, which reduce the entry of microorganisms and oxygen.
Expiry Date Vs PAO In Cosmetics: What “Minimum Durability” Really Means
The expiry date indicates the period during which the product maintains its properties when it remains unopened and stored under appropriate conditions.
It is indicated by the hourglass symbol, together with a date, or by wording such as “best used before”.
Unlike PAO in cosmetics, the product is assessed in a closed state.
When Is It Declared (Durability < 30 Months)
When the product’s minimum durability is less than 30 months, it is mandatory to declare a specific expiry date on the label.
This declaration must be supported by technical studies included in the Product Information File (PIF).
What Is Evaluated (Physical-Chemical and Microbiological)
To establish the expiry date, the following are typically assessed:
- Physical-chemical stability studies
- Evaluation of active ingredient degradation
- pH and viscosity monitoring
- Periodic microbiological testing
For products with an aqueous phase, microorganisms commonly monitored include:
- Staphylococcus aureus
- Pseudomonas aeruginosa
- Candida albicans
- Aspergillus brasiliensis
- Escherichia Coli
These studies help determine whether the product maintains its specifications over time.
In addition to basic parameters, certain products also require evaluation of the stability of UV filters, antioxidants, fragrances, or actives sensitive to oxidation. Variations in the concentration of these components may compromise not only sensory quality, but also functional efficacy and safety profile.
Physical-chemical stability should always be interpreted together with microbiological stability, especially for formulations with high water activity or complex preservative systems.
PAO In Cosmetics Vs Expiry Date: Key Differences
The key difference lies in the product state being evaluated and the type of risk considered.
| Criteria | Expiry date (minimum durability) | PAO in cosmetics |
| Evaluated state | Closed product | Opened product |
| Mandatory declaration | < 30 months | ≥ 30 months |
| Main risk | Internal degradation | Post-opening contamination |
| Key supporting studies | Accelerated + real-time stability | Post-opening assessment + preservative efficacy |
| Labelling symbol | Hourglass | Open jar |
Both concepts are complementary and must be technically justified.
PAO in Cosmetics and Expiry Date in the EU: Regulation (EC) No 1223/2009
Regulation (EC) No 1223/2009 establishes the requirements related to durability and labelling of cosmetic products placed on the EU market.
Labelling Requirements (Symbols And Cases)
- Hourglass → minimum durability date when < 30 months
- Open jar → PAO when ≥ 30 months
Incorrect use of these symbols constitutes a regulatory non-compliance.
What Must Be Supported In The PIF/CPSR
Both the expiry date and PAO in cosmetics must be supported by:
- Stability studies
- Microbiological evaluation
- Technical justification in the CPSR
- Complete documentation in the PIF
Arbitrary periods cannot be declared without experimental support.
Tests To Justify PAO In Cosmetics And Expiry Date (Stability + Microbiology)
Determining both indicators requires verifiable technical data.
Stability Studies (Accelerated And Real-Time)
These studies assess product evolution under different temperature and storage conditions.
ISO 11930 Challenge Test to justify PAO in Cosmetics (Preservative Efficacy)
ISO 11930 is fundamental to justify PAO in cosmetics, as it evaluates preservative system efficacy against inoculated microorganisms.
ISO 17516 (Microbiological Criteria)
ISO 17516 defines acceptable microbiological limits for cosmetic products, reinforcing safety throughout the product’s lifecycle.
The combination of stability studies, Challenge Test, and periodic microbiological controls enables a robust scientific justification. These tests should not be considered in isolation, but as part of an integrated risk assessment addressing product behaviour across its full lifecycle.
Critical Factors That Can Change The Outcome
Cosmetic stability does not depend only on the initial formulation. External and use-related variables can significantly alter product performance and therefore impact the declared PAO or expiry date.
Water Activity And Formulation Type (Aqueous Vs Anhydrous)
Aqueous formulations generally present a higher microbiological risk than anhydrous products.
Packaging Impact on PAO in Cosmetics (Airless vs Jar) and Secondary Contamination
Packaging design directly influences the level of risk after opening.
Common mistakes with PAO in cosmetics
Common issues include:
- Declaring a PAO without a Challenge Test
- Copying standard periods without technical justification
- Not reassessing stability after formulation changes
- Ignoring packaging influence
These errors typically stem from using standard periods without product-specific technical assessment or failing to review stability after changes in formulation or packaging. Any change in composition, preservative system, or packaging material may significantly affect stability outcomes.
SHAPYPRO Technical Approach
At SHAPYPRO, the assessment of expiry date and PAO in cosmetics is integrated within a global stability and product safety analysis. This approach combines physical-chemical testing, microbiological studies, preservative system evaluation, and packaging assessment, enabling coherent interpretation supported by documentation.
Correct differentiation between expiry date and PAO requires understanding not only regulatory requirements, but also degradation mechanisms and microbiological risks associated with each formulation type. This technical approach supports declared periods with solid data aligned with Regulation (EC) No 1223/2009.
It also enables the integration of stability, microbiology, and regulatory requirements into a single technical strategy, reducing regulatory risk and strengthening the robustness of the cosmetic product dossier.
Conclusion
PAO in cosmetics and the expiry date address different stability and risk scenarios. While the expiry date evaluates the product in a closed state, PAO assesses product behaviour after opening and under real-use conditions.
Correct determination requires robust technical studies, compliance with Regulation (EC) No 1223/2009, and an integrated evaluation of physical-chemical and microbiological factors. Only a documented scientific justification can ensure consumer safety and regulatory compliance.