Korean Sheet Mask Expiration Dates: How to Read the Stamp

You dig a foil sheet mask packet out of a drawer, leftover from an Olive Young sale you don't fully remember, and flip it over looking for a date, but none of it looks like anything printed on a Sephora shelf. Two lines of small print sit next to a tiny icon of an open jar, with a number beside it.

This one's for anyone with a backlog of half-forgotten sheet masks and serums from two sales ago. What do the numbers on the back actually mean?

The Three Numbers Korean Packaging Prints

Korean cosmetics labels run on a different system than most Western drugstore shelves, and it's not one number. It's up to three, and they don't mean the same thing.

• 사용기한, or a date followed by 까지 ("until"), is the use-by date, a hard stop, printed as YYYY.MM.DD. "2028.06.09까지" means stop using it after June 9, 2028.
• 제조일자 (or just 제조) is the manufacturing date, not an expiry. When a brand prints only this, ShopAtKorea explains, you're expected to add a standard shelf life yourself, typically three years for most products, five for pressed powders.
• The PAO symbol (an open-jar icon with a number like "12M") counts months from the day you first break the seal, not from purchase. Wikipedia's rundown of the mark is a decent plain-English reference if your product uses it.

Sheet masks mostly sidestep the third one. You crack the foil, use the whole thing, and the packet is empty, with no real "months after opening" window for something you finish in twenty minutes. The sealed 사용기한 is the number that matters on a mask, checked before the seal is ever broken.

Korea Tightened the Rules in February 2025

This isn't a static system. Multi-product sets got a small simplification in the same update. Instead of printing every item's own date, a set can list a single earliest expiration date and note "refer to individual product" for the rest. As of February 7, 2025, ChemLinked reported, Korean regulators require the manufacturing date to sit next to the PAO period wherever it's shown, with both printed clearly on the outer box of the set.

It's a smaller change than it sounds, but it closes a real gap. Before this, a boxed set could bury the actual date on packaging you'd have already thrown out. This wasn't the first tightening, either. Since February 2017, Korea has required an expiration date on sample-size cosmetics too, the little foil pouches that used to ship dateless.

Why Your CeraVe Doesn't Have Any of This

Cross the Pacific and the whole approach changes. In the US, a moisturizer's label can legally be nothing more than a batch code you'd need a decoder site to interpret. The FDA's own position, as Tangie summarizes it, is blunt: "there are no U.S. laws or regulations that require cosmetics to carry PAO symbols, expiration dates, or specific shelf lives on their labels."

Sunscreen is the exception, and the reason is regulatory, not scientific; the FDA classifies it as an over-the-counter drug rather than a cosmetic, requiring formal stability testing. Pavise's rundown of FDA sunscreen rules notes that records need to be kept "for one year after the product expiration date, or, if the product is exempt from expiration dating (most sunscreens are), for 3 years after distribution". That means most sunscreens end up testing stable enough to skip a printed date entirely. A Korean serum's label states the exact day to stop. An American one next to it might have no date on it at all.

So Is That Old Sheet Mask Still Good?

A dermatologist and an esthetician landed in different places on this when Beautytap asked them directly, answering slightly different questions rather than actually disagreeing. Dr. Ava Shamban's line was flat: "a sheet mask that appears dried out should be thrown away." Esthetician Gina Marí was more forgiving: "products typically last longer than their actual expiration dates," especially stored in a dark, cool spot.

For a single-use foil packet, the intact seal matters more than the printed calendar date. If the foil hasn't been punctured, the essence hasn't visibly dried at the edges, and it doesn't smell off, a mask a couple of months past its 사용기한 is a low-stakes gamble. A year or more past it, especially if the pack feels light or the essence has pooled unevenly, I'd skip it, and that's less about the ingredients going stale than about what a year of temperature swings in transit and storage does to the preservative system. For a jar or tube already past its PAO count, the math flips. Toss it regardless of how much is left, since contamination risk builds with every finger dip. Worth the gamble?

Check the printed date the moment the box lands, instead of waiting until it's spent another six months in your bathroom. Stock shipped by a reseller or sitting in a warehouse before reaching a buyer isn't dated from the day it arrives; it's dated from the day it was made, and it might be a year or more before the sale itself.

Go flip over whatever's actually sitting in your drawer right now. A sheet mask stamped with 사용기한 or a PAO icon already has its answer printed on it. A bare manufacturing date means doing the shelf-life math yourself.

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This is a running news series, not a one-off post — new stories go up twice a day, roughly 7am and 7pm Korea time.

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