How to Read Expiry Dates, PAO Symbols, and Batch Codes on Skincare
The little open jar symbol, the printed date, and the unexplained code on the crimp all mean different things. Which one governs when a product should be thrown away.
Turn a moisturiser over and you may find three different messages about time: a date printed on the crimp, a small open jar with 12M inside it, and a string of letters and numbers that means nothing to you at all. They are not three versions of the same information. One is a shelf life, one is a period after opening, and one is a traceability code that was never meant for you, though it is often the only one people try to decode.
Knowing which is which settles a practical question every bathroom shelf raises: is this still all right to use? The answer depends on the product type, and for sunscreen it is stricter than for anything else in the cabinet, because an expired sunscreen fails silently at the one job it exists to do.
The open jar is a clock that starts when you do
The PAO symbol, period after opening, is the open jar icon with a number of months inside it, such as 6M, 12M, or 24M. It states how long the product remains suitable after it is first opened, assuming normal storage. It appears widely on products sold in Europe and on many sold elsewhere, and it pairs with a habit almost nobody has: writing the opening date on the bottle with a marker. Without that, a 12M symbol on a product opened at an unknown time is decorative.
PAO matters most for products whose preservative system and active ingredients degrade or whose contamination risk rises with use: eye creams in jars, mascara adjacent skincare, natural positioned formulas with gentler preservation. A pump bottle of a stable moisturiser is forgiving. A jar you have dipped fingers into for a year is a different calculation, and it is why brands favour pumps for more than their appearance.
Printed dates and the sunscreen rule
Some products carry an explicit expiry date, and where one is printed it takes precedence over guesswork, whether the product is opened or not. Sunscreens sold in the United States are treated as drugs and carry expiry dates, and an out of date sunscreen should be replaced rather than used up. Its filters degrade and the tested protection can no longer be assumed. Using it because the texture looks fine mistakes a cosmetic judgement for a performance one.
Vitamin C serums and retinoids have their own version of expiry that arrives before any date. A vitamin C serum that has turned dark orange has oxidised, and its benefit has largely gone with the colour change. A retinoid that has been open, warm, and lit for a year may be well inside its printed life and well past its useful one. Storage, cool, dark, and closed, is not fussiness for these actives. It is the condition their shelf life was calculated under.
Batch codes are traceability, not a puzzle for consumers
The long code stamped on a bottle is a lot or batch code. Its purpose is manufacturing traceability, so a brand can identify a production run if a problem is reported. Brands use different formats, websites claim to decode them into manufacture dates, and those decodings are unreliable enough that they should not be the basis for throwing away an in date product or trusting an old one.
If you genuinely need to know, ask the brand with the code in hand. They can read their own system, and a reputable one will. Otherwise, work from the evidence you control: the printed expiry where there is one, the PAO from a date you recorded, and the product's own smell, colour, and texture. A change in any of those three is a reason to stop using a product even inside its dates, particularly anything applied near the eyes.
Related reading: How to Store Vitamin C Serum So It Actually Lasts, What Is Squalane and Who Should Use It, What Is Micellar Water For, and Should You Rinse It Off?.
Frequently asked questions
What does 12M in an open jar symbol mean?
It is the period after opening: the product is intended to be used within 12 months of first opening, under normal storage. Writing the date you opened it on the bottle is the only reliable way to use the symbol.
Which takes priority, the PAO or a printed expiry date?
A printed expiry date governs the product whether opened or not. The PAO governs the period after opening. Use whichever point arrives first, and treat changes in smell, colour, or texture as a separate reason to stop.
Can you use sunscreen after its expiry date?
It should be replaced. Sunscreen protection is tested to that date and filters degrade over time, so an expired product cannot be assumed to deliver its labelled protection even if it looks and smells normal.
Can a batch code tell you when a product was made?
Not reliably for a consumer. Batch codes are manufacturer traceability codes in brand specific formats. Online decoders are inconsistent. If the date matters, ask the brand directly with the code.