How to Read the PAO Symbol on Your Skincare Products

Flip almost any skincare or makeup container over and, somewhere among the ingredient list and manufacturing details, you'll find a small icon that looks like an open jar with a number and the letter "M" inside or beside it. Most people have seen it hundreds of times without knowing what it actually means. It's called the Period-After-Opening symbol, or PAO symbol, and once you know how to read it, it tells you something a printed expiration date never can.

What the Symbol Actually Says

The open-jar icon represents the product's container, and the number inside it — followed by an "M" — indicates how many months the product is considered good for once it's opened and in active use. A jar marked "12M" means the manufacturer estimates the formula remains stable and safe to use for twelve months after you first break the seal. A jar marked "6M" means six months from that same starting point. The symbol doesn't tell you when the product was manufactured or when it will go bad on a shelf while still sealed — it's specifically counting from the moment air, light, and repeated use start affecting the formula.

PAO vs. a Printed Expiration Date

These are two different pieces of information, and mixing them up is one of the most common skincare shelf-life mistakes. A printed expiration date (sometimes shown as a "best before" date near a manufacturing batch code) reflects how long an unopened, sealed product remains stable under normal storage conditions — it's a countdown that starts at manufacturing and keeps running whether or not you ever open the bottle. The PAO symbol is a separate countdown that only starts once you open the product, and it's typically a shorter window than the unopened shelf life, because an open container is exposed to air, bacteria, and light in a way a sealed one isn't.

In practice, this means a product could have years of unopened shelf life remaining and still be past its safe-use window if it's been open on your shelf for far longer than its PAO number suggests. The two numbers work independently, and PAO is the one that matters most for a product you're actively using.

The PAO Numbers by Product Type

PAO windows vary by category based on how a formula is built and how it's typically used, and the Expiry Date Tracker uses these standard industry windows to calculate an actual expiry date once you enter your open date:

• Mascara: 6 months — the shortest window, because the applicator moves in and out of the tube repeatedly, pumping air in and introducing whatever was on your lashes back into the formula.
• Eye cream: 6 months — small packaging, frequent application, and use near a sensitive area all shorten the safe window.
• Sunscreen: 12 months — a longer window, though the active ingredients that block UV can still degrade with repeated air and heat exposure.
• Moisturizer: 12 months — a fairly standard window for most water-and-oil emulsion formulas.
• Serum: 12 months — though some individual active ingredients inside a serum can be more sensitive than the base formula itself.
• Cleanser: 12 months — rinsed off quickly and often surfactant-based, cleansers tend to be fairly resilient.
• Foundation: 12 months — similar profile to moisturizer.
• Lipstick: 18 months — the longest window here, thanks to a largely wax-and-oil-based, low-water formula that's naturally less hospitable to bacterial growth.

Turning the Symbol Into an Actual Date

The PAO symbol only gives you a duration, not a date — which means it's only useful if you also know when you opened the product. This is the step people skip, and it's the one that actually makes the symbol usable. The moment you open something new, jot the date down: a strip of tape on the bottom of the container, a note in your phone, or an entry in the Expiry Date Tracker. From there, the math is simple addition — open date plus the PAO window from the symbol equals your expiry date. A moisturizer marked "12M" and opened on March 1st is due for replacement around March 1st the following year, regardless of how much product visibly remains in the jar.

Why Manufacturers Don't Just Print a Fixed Date Instead

A fixed printed expiration date would need to assume a specific opening date, which manufacturers obviously can't know in advance — the same tube of sunscreen might sit sealed in a drawer for eight months before you crack it open, or get used the day you buy it. The PAO symbol solves this by putting the countdown in the consumer's hands: it travels with the product regardless of purchase date, and it only starts counting once you actually start using it, which is a more accurate reflection of how the product is aging in real use.

Don't Confuse It With Nearby Symbols

The PAO icon usually sits among several other small symbols on packaging, and it's worth knowing which is which so you're reading the right one. A batch code — often a short string of letters and numbers, sometimes stamped rather than printed — identifies the specific production run and is mainly used by manufacturers for quality control and recalls; it's not a date you can read directly, though some brands' batch codes can be decoded into a manufacture date if you look it up. Symbols like a small leaping rabbit (cruelty-free testing status) or a recycling triangle (packaging material) are common neighbors of the PAO symbol but have nothing to do with shelf life at all. If you're scanning a label for the first time, look specifically for the open-jar outline — that's the one with the months-and-M format that matters for tracking expiry.

Two Products, Two Very Different Timelines

Seeing the difference play out side by side makes the symbol's purpose clearer. Say you open a lipstick and a mascara on the same day. The lipstick's "18M" symbol means it's good to use for a year and a half from that date — plenty of time for even light, occasional use to work through it completely. The mascara's "6M" symbol means it needs replacing a full year earlier, even though both products were opened on the same day and even if the mascara wand still looks like it has plenty of product left. Without checking each symbol individually, it would be easy to assume both products age at the same rate simply because they were opened together — which is exactly the assumption the PAO symbol exists to correct.

What to Do if You Can't Find the Symbol

Some products, particularly older formulations, smaller indie brands, or certain product categories, don't include a PAO symbol at all. In that case, the standard category windows above are a reasonable default to apply on your own — treat an unlabeled mascara as a 6-month product, an unlabeled serum as a 12-month product, and so on, based on how similar products in that category are typically formulated. It's an estimate rather than a manufacturer guarantee, but it's a far better anchor than guessing with no reference point at all.

The Bottom Line

The PAO symbol is one of the more useful pieces of information printed on a cosmetic product, and one of the least understood. It's not a manufacturing date, and it's not the same as a printed expiration date — it's a countdown that starts the moment you open the product and runs for however many months the icon specifies. Pair that number with a written record of your own open date, whether that's a piece of tape or a tool like the Expiry Date Tracker, and you have a genuinely accurate picture of when each product in your routine is due for replacement.