Period after opening

Skincare carries a date that most other products do not: how long it remains good once the customer has opened it. Getting it right is a preservation decision and an honesty decision at the same time.

Two different dates

Shelf life is how long the unopened product remains within specification, and it comes from stability testing. Period after opening is how long it lasts once the seal is broken and the customer starts using it, and it comes from the preservation system and the package.

They are different numbers with different evidence behind them, and a product can have a long shelf life and a short period after opening.

What decides the number

How much the package exposes the product. An open jar is re-inoculated by fingers on every use and sits open to the air; a pump removes the fingers; an airless system removes the air as well.

And how much margin the challenge result showed. A comfortable pass supports a longer period; a marginal one is exactly the circumstance where a short declared period is part of how the product is kept safe.

Actives shorten it further

Preservation is not the only clock. L-ascorbic acid degrades in oxygen, light and heat, so an L-ascorbic acid serum commonly has a usable life of four to six months once opened, while a stable derivative such as MAP, ascorbyl glucoside or THDA holds for twelve months or more.

That is a formulation choice with a direct consequence for what you print and for what the customer experiences in month five.

What to print

A number you can stand behind rather than a number that looks generous. Twelve months on a product that is visibly oxidized at five is worse than six months honestly stated, because the customer meets the truth either way and only one version keeps your credibility.

And write the reasoning into the product record. A period after opening that nobody can explain is a number that will be quietly extended by somebody later.

References