Determining PAO

Can someone advise what factors are considered when determing a PAO of a product or at least point me in the direction where I can find this information?

Thank you for your time and responses.


  • johnbjohnb Member, Professional Chemist
    Is my brain failing me?

    I don't have a clue as to what PAO is, and Goooogle is unable to give me a reasoned explanation.
  • MakingSkincareMakingSkincare Member, Professional formulator
    John it means "period after opening" (EU Cosmetic Regs).  befremovska: You will need to conduct stability and PET tests to determine the shelf life.  If the shelf life is less than 30 months it must be labelled with a best before date (date of minimum durability). If the shelf life is greater than 30 months best before is not required, and the Period After Opening (PAO) is indicated using the “open jar” symbol. But PAO is not applicable to certain product eg anhydrous, single use packs.

    Jane Barber (free online course)
    Formulation discussion forum (18,000 members):
  • johnbjohnb Member, Professional Chemist
    Jane, thanks for that.

    Shows how easy it is to lose track with all of these EU regs!

    Obviously, I am unable to help.
  • Bill_TogeBill_Toge Member, Professional Chemist
    the main factors determining PAO are how well the product keeps once the pack has been opened (e.g. does it dry out over time), and the risk of microbial contamination from normal use

    for instance, if the consumer has to put their finger in the pack to dispense the product, it will have a shorter PAO than the same product in a tube, which is essentially a one-way dispenser and much harder to contaminate

    there are no rigorous rules to determine it: it is essentially an educated estimate

    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
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