The serum that stopped working may not have stopped working — it may have expired. Skincare has a shelf life that most people never check, and an oxidised product does not just do nothing: some of them actively work against you.
Where to find the real date
Look for a small open-jar symbol on the back, with a number and the letter M: 6M, 12M, 24M. That is how many months the product lasts after you open it, and it is the number that matters. The printed expiry date refers to an unopened product sitting in a warehouse.
Which means the date is only useful if you know when you opened it. Write the month on the bottom of the bottle with a marker when you start it. This takes four seconds and settles the question permanently.
Realistic lifespans once opened
- Vitamin C (L-ascorbic) — three months, and less in a dropper bottle you open daily. The shortest-lived thing on your shelf.
- Retinoids — six months to a year, kept away from light.
- Sunscreen — the printed date, and that one is not negotiable: degraded filters give less protection than the label claims.
- Moisturisers and cleansers — six to twelve months.
- Oils — six months to a year. Rosehip oxidises fastest.
- Anything in a jar you put fingers into — shorter than the label says, because you reinoculate it every morning.
How to tell without a date
Colour change is the clearest signal: vitamin C going yellow then amber then brown, a white cream turning cream-coloured, an oil darkening. Then smell — a sharp, waxy or crayon-like note in something that used to smell of nothing. Then texture: separation, grittiness, a cream that has gone watery.
Any one of those means it goes. A product that has separated has not just aged — its preservative system may no longer be distributed through it.
Storage buys you months
The bathroom is the worst place in the house for skincare: heat and humidity shorten everything, especially actives. A bedroom drawer costs nothing and genuinely extends shelf life.
Close lids properly, keep products out of direct light, and prefer a pump or tube over a jar when you have the choice. Do not decant into prettier containers — you lose the packaging that was protecting the formula.
And buy the size you will actually finish. A large bottle of vitamin C is cheaper per millilitre and more expensive in practice, because the last third of it was doing nothing by the time you got there.