Does skincare expire, and what the PAO symbol means

Updated: 2 October 2026

Yes, and the package says so in one of two ways. Either it carries a best-before date — the date until which the product, stored properly, will go on doing what it was sold to do — or it carries an open jar with a number and the letter M, which is a span counted from the day you first opened it rather than from the day you bought it.

The two marks, and why a package carries only one

European rules give a package two ways to say this, and most packages use only one of them. The first is a date, introduced either by the small hourglass the rule sets out in its annex of symbols, or by the words “best used before the end of”. The rule defines that date precisely: it is the date until which the product, stored under appropriate conditions, will continue to fulfil its initial function. A month and a year is enough, and the rule allows either month and year, or day, month and year.

The second is an open jar with its lid lifted off, followed by a number and the letter M. That one is not a date but a span. The rule describes it as the period of time after opening for which the product is safe and can be used without any harm to the consumer, and it is given as that symbol followed by the period in months, or in years.

One threshold decides which mark a package needs. Where the minimum durability is more than thirty months, the date stops being mandatory and the open jar stands in its place. So a product the maker expects to keep for years tends to show you the open jar, and one with a shorter life tends to show you a date. A package carrying both is being more generous than it has to be.

Some packages carry neither, and that is in the rule rather than a slip: the open jar is not required where durability after opening is not a relevant concept. A single-use sachet is the easy example, because there is no after-opening to measure.

How to read the open jar

Read the letter as well as the number. M stands for months, in English and in several other European languages at once, which is why the symbol travels without translation. And because the rule permits the period in months or in years, the letter is the part that tells you which unit you are holding.

Where the symbol trips people up is the start. The clock starts when you open the product. Two identical tubes bought on the same afternoon, one opened that evening and one left in a drawer until spring, sit at completely different points on the same open jar, and nothing printed on either tube tells them apart.

So the open jar is half a fact. The package gives you the span; the start date is yours, and the package has nowhere to keep it. That makes this a memory problem rather than a reading problem, which is worth knowing before you go looking for an app that solves it by reading.

It is also often not printed where you look first. Frequently it is on the outer carton rather than on the bottle inside it, which is a good reason to read the carton before it goes in the bin. On jars and lids it is often moulded into the plastic in the same colour as the plastic, legible only when you tilt it against the light. On a tube, look at the flattened crimp at the sealed end.

The batch code is not a date

Near the marks there is usually a short run of letters and numbers with no symbol in front of it. The same labelling rule asks for that too, as the batch number of manufacture or the reference for identifying the cosmetic product. Its job is to point at one production run, so that run can be identified later.

It is not a date, and nothing in the rule asks it to be one. Sites that offer to turn a batch code into a date of manufacture are reading a scheme they were never handed, maker by maker. The date a maker will stand behind is the one printed as a date; where no date is printed, the package is telling you a period after opening instead, on purpose.

What the United States requires, and what it does not

Far less. The FDA states it without qualification: there are no US laws or regulations that require cosmetics to have specific shelf lives or expiration dates on their labels. Working out a shelf life is something the FDA considers part of the maker's own responsibility, rather than something the label is compelled to publish.

The FDA's definition of the term is worth having in its own words, because it is wider than people assume. A product's shelf life “generally means the length of time you can expect a product to look and act as expected and to stay safe for use”. That is a statement about the product, and a European mark is a boundary drawn on exactly that statement.

Sunscreen is the real exception, because in the United States it is regulated as an over-the-counter medicine and not only as a cosmetic. Products in that category must carry an expiration date unless the maker's stability testing has shown the product stays stable for at least three years, and where a sunscreen carries no date at all, the FDA's own advice is to count it as expired three years after purchase.

What the date is actually a promise about

Look again at what the European definition promises, because the wording is narrow: the product will continue to fulfil its initial function. Function. The mark is the outer edge of the maker's own claim about what the product does, and past that edge the maker has stopped making it.

The same sentence carries its own condition: stored under appropriate conditions. Storage sits inside the promise rather than in a footnote beside it. The rule even lets a maker spell out the conditions that have to be met for the stated durability to hold, which tells you how much work that clause is doing.

What happens after the date is not printed on the package, and this page is not going to print it on the maker's behalf. The two things a package genuinely hands you are a span and a condition, and both beat any general rule about how long skincare lasts, because both were written for the one formula in your hand. Where a carton or a leaflet names a period, that period wins over anything a page like this one could say.

Where Glossa fits on this

Glossa keeps the list of what is actually on your shelf: every product you use, each one a thing you can see rather than a line you typed once and forgot. Holding that list is the tedious part of this job, and it is the part a phone is good at.

Products get onto the shelf from one photo of them. What the photo reads is matched against a catalog of 19,550 products from 6,006 brands, and if something is not in there you add it by hand. Typing your shelf in works exactly as well as the photo.

Dates are a different job, and Glossa leaves them with you. It holds the list of your products; the marks on their packaging stay on the packaging, and reading them is yours. An app that offered to count the months since you opened a bottle would be offering to know a date nobody ever wrote down.

What it does instead is put you in front of your shelf twice a day. Your products stand on an illustrated shelf with a mirror above it, and each step of your routine plays as a small scene in that mirror. The morning you reach for a bottle is the morning you are holding it, and that is when the open jar on its base is actually readable.

What Glossa does not do

Glossa is not a health product. It does not look at your skin, and it does not tell you what to put on it.

Glossa shows the routine you built. It does not build one for you.

Dates and periods after opening live on your packaging. Glossa holds the list of what stands on your shelf.

iPhone only, and Android is not planned.

Glossa at a glance

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