PAO - The Period After Opening

The PAO (Period After Opening) symbol is now commonly found on packages of creamy or liquid cosmetic formulations - it indicates how long the product is safe for use after opening. My question is, is there a good rule/method to determine that time? How different it is from the shelf life? I understand that it strongly depends on the type of packaging: for example, for a cream in a jar opening means that product is subjected to oxidization and microorganism attack, so PAO should somehow reflect the 'best before' time for the antioxidants and preservatives in the formula. But what about pump bottles? Airless bottles are even more interesting - what would PAO mean for those?


  • anaitanait Member
    edited August 2015
    Thanks a lot, ozgirl ! That second doc has actually answered all my questions ;)
  • PAO is a technically-invalid and ridiculous concept that has been exploited by some to justify marketing of unstable products.  Oxygen is present in the had space of every product as it's package and any chemical instability will begin the moment ingredients are combined - not when  package is opened.  PAO will be blind to degradation of the time from manufacturing to 1st use. Further, consumer contamination is episodic and based on specific actions of consumers - not the time of use.  
    Importantly, consumer pay little to no attention to such labeling.
  • MarkBroussardMarkBroussard Member, Professional Chemist
    PAO applies to products with a shelf life of 30 months or more ... if your product requires a shelf life of 30 months or more, you have a sales & marketing problem, not a product stability problem.  For most consumers, the PAO is when the container is completely empty after they have used all of the product.

    This reminds me of the expiration date on fresh food products ... it's an estimate of "peak" freshness, but supermarkets discard tons of perfectly good food products daily when this expiration date is hit.  Such a waste.    
    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details
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