Period After Opening (PAO)

The period after opening is the small open-jar symbol on a pack, with a number and the letter M — 6M, 12M, 24M. It states how many months the manufacturer expects the product to remain in good condition once it has been opened and exposed to air, skin and bathroom conditions.

It is a different claim from an expiry date. An unopened product has its own shelf life; the PAO clock only starts at first use. Products with a shelf life under thirty months carry a date instead, which is why some packs show one and not the other.

• The figure is the manufacturer's estimate under ordinary use, not a laboratory guarantee for any particular jar.
• Dipping fingers into an open pot introduces microbes that a pump or tube would not, so packaging affects real-world life as much as the number does.
• Water-free products such as balms and oils have different failure modes; they are more likely to go rancid than to grow microbes.

Trust the product over the symbol when they disagree. A change in smell, colour, or texture, or separation that was not there before, means a product has changed regardless of what month it is in — and a sunscreen or an eye product past its window is not worth the risk of using anyway.