PAO stands for Period After Opening. The symbol looks like a small open cosmetic jar with a number and the letter M inside — 6M, 12M, 24M. It tells you how many months the manufacturer expects the formula to stay stable and safe once air, fingers and bathroom humidity reach it.
The clock starts at first use
A 12M product that has sat sealed in a drawer for two years has, in principle, not started its PAO countdown. But sealed does not mean frozen in time — heat, sunlight and the natural instability of certain ingredients still age a formula. PAO and shelf life are two separate clocks, and both matter.
Typical PAO by product type
- Mascara and liquid liner: 3M to 6M — the highest-risk category for eye infections
- Liquid foundation and concealer: 6M to 12M
- Cream blush, cream shadow and lip gloss: 12M
- Powder products (pressed and loose): 18M to 24M or longer
- Lipstick and lip liner: 12M to 24M
- Water-based serums and moisturisers in jars: 6M to 12M
- Airless pump skincare: 12M and often longer thanks to reduced air exposure
- Sunscreen: follow the printed expiration date, not just PAO
- Fragrance: usually no PAO; well-stored juice lasts years
What PAO does not cover
PAO assumes reasonable storage: room temperature, out of direct sun, cap closed, clean applicators. A foundation left in a hot car for a summer is past its useful life regardless of the number on the label. Conversely, an unopened, cool-stored powder can outlive its PAO comfortably.
Signs to stop using a product now
- Smell change — rancid, sour, or a sudden loss of fragrance
- Separation that does not re-mix when shaken
- Colour shift, especially darkening in vitamin C or retinol products
- Texture change: grainy, tacky, or unusually thin
- Any visible mould or a dry film on the surface of a cream
- Stinging or irritation from a product you previously tolerated
Reading PAO as a reseller or buyer
In a listing, state whether the product is sealed, swatched once, or gently used, and pair it with the PAO number and the batch code estimate. Buyers overwhelmingly prefer an honest "opened, roughly 3 months into a 12M PAO" over a vague "like new".