Storage is decided by the formula, not the headline ingredient
The studies behind our ingredient pages — for example, a four-week betaine cream study or a 28-day PDRN eye-cream study — were run under controlled conditions to measure skin outcomes, not shelf life. They do not support a per-ingredient temperature rule. Storage guidance belongs to the finished product's label and official page.
Read the open-jar symbol and the date
In the EU, cosmetics with a shelf life over 30 months carry the open-jar (period-after-opening) symbol instead of a best-before date — the number with “M” (for example, “12M”) shows how many months the product remains suitable after first opening. The regulation excepts cases where the concept does not apply, such as single-use products. In the US, the FDA notes no law requires expiration dates on cosmetics — but sunscreens and acne treatments are regulated as drugs (or both) and must meet stability requirements, so check the expiration date on those. For any product: note when you open it, and follow what its maker says about the symbol or date on that pack.
Cap closed, cool and dry
Keep the cap closed and avoid warm or damp storage — a steamy bathroom shelf is a common example when the label warns against heat or humidity. These are label-aligned basics, not ingredient-specific rules.
A finished product is not a raw ingredient
Some finished cosmetics foreground one extract, ferment, or filtrate. A “100%” or high-percentage front label still does not replace the complete ingredient list, the preservation system, pH, or directions. Treat it as a finished formula, not a raw material.
A few useful answers
Should I keep my serum in the fridge?
Start with the manufacturer’s storage directions — they take priority over any general tip. None of the ingredient studies cited here tested home refrigeration, so there is no evidence-based fridge rule from them. Refrigeration does not upgrade a product’s proven results; it is only worth doing when the maker directs it.
What does the open-jar symbol mean?
It shows the period after opening (PAO) — for example, “12M” means 12 months after opening, according to the manufacturer. It is not the date the product was made.
Does a high percentage mean it spoils faster?
Not necessarily. How long a product keeps depends on the preservation system and packaging of the finished formula, not the headline percentage alone. The full ingredient list and the PAO symbol are more informative than the front label.