Lumiere
Somewhere on your moisturiser there's a small icon of an open jar with a number inside it: 6M, 12M, 24M. That's the PAO — period after opening — and it's the manufacturer's own statement of how long the product stays safe and effective once air first reaches it.
It's the most actionable number on the whole package, and it's useless unless you know when you opened the thing.
The PAO symbol, decoded
Two dates govern every product you own, and they're not the same:
| Expiry / best before | PAO | |
|---|---|---|
| Clock starts | At manufacture | The day you break the seal |
| Shown as | A printed date, or an hourglass icon | Open-jar icon with 6M, 12M, 24M |
| Applies when | Products with a shelf life under 30 months | Products stable for 30+ months unopened |
| What ends it | Chemical degradation on the shelf | Oxidation and microbial load after opening |
Both matter. An unopened serum bought three years ago can be past it before you ever use it. A sunscreen opened last summer is past it even if the printed date is next year.
The full shelf life chart
These are typical manufacturer PAOs. The number printed on your bottle always wins — but when the packaging has worn off or you bought a decant, this is the sensible default.
| Product | Typical PAO | Notes |
|---|---|---|
| Vitamin C serum (L-ascorbic acid) | 1–3 months | The shortest life in skincare. Oxidises on contact with air and light; turns yellow then orange then brown. Derivatives such as ascorbyl glucoside or THD ascorbate last far longer. |
| Eye cream (jar) | 6 months | Small opening, repeated finger contact, delicate area. Be strict with this one. |
| Micellar water | 6 months | Water-based with a light preservative system. |
| Face oil | 6–12 months | Unsaturated oils go rancid. Rosehip and grapeseed are fastest; squalane and jojoba are very stable. |
| Retinol / retinal serum | 6–12 months | Degrades with light and air. Opaque, airless packaging roughly doubles the useful life. |
| Moisturiser (jar) | 6–12 months | Every dip introduces microbes. Use a clean spatula and you'll get the upper end. |
| AHA / BHA exfoliant | 6–12 months | Acids are fairly stable but pH can drift over time. |
| Sunscreen | 12 months | Or the printed expiry, whichever is sooner. Heat exposure shortens it sharply. Full detail here. |
| Moisturiser (pump / tube) | 12 months | No finger contact, minimal air — meaningfully longer than the same formula in a jar. |
| Niacinamide serum | 12 months | Niacinamide is one of the most stable actives available. |
| Hyaluronic acid serum | 12 months | Stable, but water-based and preservative-dependent. |
| Cleanser | 12 months | Rinse-off and heavily preserved. Generous life. |
| Toner / essence | 6–12 months | Shorter if it contains alcohol that can evaporate and shift the formula. |
| Clay mask | 12–24 months | Low water content, very stable. Discard if it dries out and cracks. |
| Sheet mask | Use printed date | Individually sealed, so PAO barely applies. Discard immediately after opening. |
| Lip balm (stick) | 12–24 months | Anhydrous and waxy. Discard sooner after any cold sore. |
| Anything prescription (tretinoin, azelaic) | Pharmacy date | Follow the dispensing label, not a cosmetic PAO. |
Why packaging changes everything
Two identical formulas can have very different real-world lives depending on what they're sitting in. Packaging controls the two things that kill products: air and fingers.
| Packaging | Air exposure | Contamination | Effect on life |
|---|---|---|---|
| Airless pump | Minimal | None | Best case — the full stated PAO, often more |
| Tube | Low | Low | Very good |
| Standard pump bottle | Some (air replaces product) | None | Good |
| Dropper bottle | High — a full air exchange every use | Moderate if the tip touches skin | Reduced, especially for vitamin C and retinol |
| Open jar | High | High | Worst case — assume the low end of the range |
This is why a vitamin C serum in a clear glass dropper bottle on a sunny bathroom shelf may be spent in six weeks, while the same actives in an opaque airless pump in a drawer are still working at four months.
Storage, briefly
- Away from the shower. Bathroom humidity and heat swings are the standard enemy. A bedroom drawer is a better home for actives than a steamy shelf.
- Out of direct light. Especially retinoids and vitamin C.
- Fridge: sometimes. It genuinely helps vitamin C and face oils. It can destabilise emulsions and oil-based products, which may separate or go grainy. Don't refrigerate by default.
- Lids on, tightly. Unglamorous, and the single highest-impact habit on this list.
How to tell something has turned
The dates are guidance. Your senses override them in both directions.
- Colour. Vitamin C going yellow → orange → brown is the clearest signal in skincare. White creams turning beige is another.
- Smell. Rancid, sour, metallic or simply "not how it smelled". Oils in particular announce their death by smell.
- Texture. Separation, graininess, thinning, clumping, or sudden pilling under makeup.
- Behaviour. A product that used to sink in and now sits on top, or that starts stinging when it never did.
- Anything visibly growing. Discard immediately, no judgement call needed.
The breakout nobody diagnoses
If a routine that worked suddenly stops working — new congestion, unexplained irritation, products that won't absorb — check the dates before you change the routine. An expired product in an otherwise good lineup is a common and completely invisible cause, because nothing in the bathroom tells you it happened.
A ten-second tracking system
You only need to solve one problem: knowing when you opened something.
- Marker on the bottle. Write the date on the base the day you open it. Free, reliable, ugly.
- Dot stickers. Slightly less ugly, same idea.
- An app. Log the product and the opening date once; get a countdown for each item and a notification before it lapses. This is exactly what Lumiere's shelf-life tracker does, and why it exists — the PAO number is only useful paired with a start date, and nobody remembers start dates.
Want to check a single product right now without installing anything? Use the free skincare expiry calculator.
Frequently asked questions
What does 12M mean on skincare packaging?
It's the period-after-opening symbol: the product stays safe and effective for 12 months from the day you first open it. The clock starts at opening, not at purchase, and it runs alongside any printed expiry date — whichever runs out first is your real limit.
How long does vitamin C serum last after opening?
Usually one to three months for pure L-ascorbic acid, which is the shortest life of anything in a typical routine. It oxidises on contact with air and light, turning yellow, then orange, then brown. More stable derivatives such as ascorbyl glucoside or tetrahexyldecyl ascorbate last considerably longer.
Can I still use skincare after the PAO date?
For a rinse-off cleanser, probably without incident. For an active such as vitamin C or retinol it will have lost potency, so you're applying an expensive placebo. For sunscreen and anything used near the eyes, replace it — the downside is real. If it has changed colour, smell or texture, discard it regardless of dates.
Does skincare last longer in the fridge?
For some products, yes. Vitamin C serums and face oils genuinely benefit from cold, dark storage. But refrigeration can destabilise emulsions and thicker oil-based creams, causing separation or graininess, so it isn't a universal rule. Don't refrigerate by default.
Why does the same cream last longer in a pump than a jar?
Air and fingers. A jar exposes the whole surface to oxygen every time you open it and introduces microbes with every dip, which is why the same formula typically carries a shorter effective life in a jar than in an airless pump or tube.
What happens if I use expired skincare?
Most often nothing dramatic — the product simply stops working, because the actives have degraded. The two real risks are irritation from oxidised ingredients, and microbial contamination in a product whose preservative system is exhausted, which matters most around the eyes and on broken skin.