Reviewed November 6, 2026

Your Moisturizer Expired Months Ago: The PAO Symbol and the Sniff Test

That moisturizer has a clock on it, printed as a tiny open-jar symbol with a number: 6M, 12M, 24M. That is the period after opening, and it is the date that matters, not the one stamped on the box. Once it passes, the preservatives are the first thing to go, and the formula is no longer the one that was tested.

Most people never notice the symbol, because it is small and printed near the barcode or the crimp of the tube. The date on the box is the unopened shelf life, usually two to three years. The jar symbol is the real deadline, and it starts the day you open the product, not the day you buy it.

How to read the jar symbol

The open-jar symbol shows a number followed by M, for months. 12M means the product is meant to be used within twelve months of opening. Vitamin C serums and retinoids often carry 6M, because their actives degrade faster. A moisturizer with 24M is a stable formula in a pump bottle, not a promise that it lasts forever.

Unopened products last longer, but they still expire. Heat and light degrade formulas on the shelf, and a serum bought on sale may already be a year into its life. Write the opening date on the bottom of the bottle with a marker. It takes five seconds and it is the only way the symbol means anything in practice.

The three signs it is done

Smell is the first sign. Oils go rancid, and a moisturizer that smells off, sharp, or different from when you opened it has turned. Texture is the second: a cream that has split, gone grainy, or thinned out has lost its emulsion, and the preservatives went with it. Color is the third, and it matters most for vitamin C: a clear serum that turns orange or brown has oxidized, and the L-ascorbic acid in it is spent.

Any one of those signs is enough. A product that smells wrong, looks wrong, or feels wrong is done, whatever the symbol says. The symbol is a guide. Your nose is the test.

Storage is half the expiry

Bathroom humidity and heat shorten every product's life. Vitamin C belongs away from light and air, in a dark bottle, closed tightly, ideally not in a steamy bathroom. Pump bottles beat jars, because a jar gets a finger in it twice a day and every dip is a new chance for contamination. If you love a jar product, use a clean spatula and keep the lid on.

Frequently asked questions

Can I use expired sunscreen?

You should not rely on it. Expired sunscreen may not deliver the SPF on the label, because the UV filters degrade over time. The risk is a burn you thought you were protected from. Replace it, and write the opening date on the next bottle.

Does unopened skincare expire?

Yes, more slowly. Unopened products typically last two to three years from manufacture, but heat and light shorten that. Check the printed expiry or batch date, and be suspicious of any product that smells off the first time you open it.

How do I know if my vitamin C serum has oxidized?

Color. A fresh L-ascorbic acid serum is clear or very pale yellow. When it turns orange, then brown, the vitamin C has oxidized and the product has lost most of its activity. An oxidized serum is not dangerous, but it is no longer doing the job you bought it for.

Is it safe to use a moisturizer past its PAO date?

It is usually not dangerous, but it is no longer the tested product. The preservatives weaken first, which raises the chance of contamination, and the actives fade. If it smells, looks, or feels different, throw it out. If it seems fine and it is a plain moisturizer a month past the date, the risk is low, but the benefit is fading.