A cosmetic's shelf life is the time it stays safe, stable and performing as intended in its unopened pack. It is set by stability and preservative testing, not by guesswork. The period after opening (PAO) is how long it stays safe once the consumer starts using it. Both numbers must be backed by data before they go on your label.
Shelf life is one of the questions indie founders ask us last and regret most. A number on a label feels like a formality, but it is a claim about your product, and it needs evidence behind it. This guide explains the difference between the terms, how a chemist arrives at each figure, and what to plan for if you sell in NZ, Australia, the EU or the US.
What is the difference between shelf life, expiry date and PAO?
Shelf life (called date of minimum durability in the EU) is how long an unopened product in its final pack remains stable. The expiry or best-before date is that shelf life written on the pack as a date. The PAO is shown as an open-jar symbol with a number of months, for example 12M, and covers the time after first opening, when air, fingers and water introduce contamination risk.
They answer different questions. Shelf life asks whether the formula and pack hold together over time. PAO asks whether the preservative system keeps the product safe under real-world use.
How do you work out a cosmetic's shelf life?
Shelf life comes from stability testing: samples are held at several temperatures, typically including elevated conditions, and checked for changes in appearance, colour, odour, pH and viscosity. Accelerated results give an early indication, and real-time stability confirms the claim. A common approach is to launch with a conservative figure and extend it as real-time data builds up.
The pack matters as much as the formula. A formula that is stable in glass can behave differently in a pump bottle or a tube, which is why packaging compatibility testing belongs in the same conversation.
How do you set a PAO?
PAO is driven by the preservative system and the way the product is used. A pump serum that never touches fingers carries a different risk from a jar of cream scooped with a fingertip. Preservative efficacy testing (challenge testing) shows whether your preservatives hold up when the formula is deliberately contaminated. We quote preservative efficacy testing at NZ$1,200 per formula. Your chemist then recommends a PAO that the data and the pack design can support.
Packaging choices can lengthen a PAO. Airless pumps and tubes limit contamination, so they often support longer PAOs than open jars.
Do NZ and Australian brands have to print an expiry date?
The EU has a clear rule: products with a minimum durability of less than 30 months need a date, and products above that use the PAO symbol instead. For NZ and Australia, we could not find a blanket, mandatory expiry-date rule in the sources we checked, and the recent NZ Cosmetic Products Group Standard update focused on ingredient restrictions rather than date marking. Consumer guidance in Australia also says there is no general legal requirement for an expiry date on cosmetics.
That does not mean you can skip the work. Your product information file should document the shelf life basis, retailers often ask for dates or batch codes, and a batch number with a date is what makes a recall manageable. Always confirm current requirements for your product type with your chemist before printing labels, because therapeutic and sunscreen products follow different rules.
What changes if you export to the EU or US?
If you plan to export, design your labelling to the strictest market from the start. The EU requires either a date or the PAO symbol depending on the 30-month threshold, and only one of the two is shown. Our guide to exporting to the EU and UK covers the wider requirements. Reformatting labels later costs far more than getting the shelf life data right now.
What can shorten a product's shelf life?
Several things, and most are within your control: heat during shipping and storage, sunlight through clear packs, oxidation-prone oils and actives such as vitamin C, weak or incompatible preservatives, and packaging that lets in air or moisture. Natural and waterless formulas each have their own risks, so the testing plan should match the formula, not a template.
How does this fit into working with The INCI Lab?
Stability and preservative testing sit inside the R&D stage of every pathway. On The Accelerator (4 to 6 months, starting from NZ$2,000 to NZ$5,000) and The Visionary (9 to 12 months, starting from NZ$4,000), we plan the testing so that your shelf life and PAO are supported by data before manufacturing. MOQs start at 100 to 500 units, and on The Visionary you own the full IP. Not sure what your current formula needs? Ask The Chemist for a 30-minute consult at NZ$150.
Frequently asked questions
What is a normal shelf life for skincare?
Many water-based creams and lotions are designed for around 24 to 36 months unopened, but the real figure depends on the formula, preservative system and pack. It should come from your stability data.
Can I use the same PAO as another brand?
No. A PAO belongs to your formula and your packaging. Copying a competitor's number without testing leaves you without evidence if a product is ever questioned.
Does a natural or preservative-free product have a shorter shelf life?
Often, yes. Waterless formulas can last well, but anything containing water needs an effective preservative system, and the testing should prove it.
Do I need stability testing before I sell?
Yes. Stability data is the basis for your shelf life and is a core part of the safety documentation for NZ, Australian, EU and US markets.
Can I extend my shelf life after launch?
Yes, if real-time stability data supports it. Many brands launch conservatively and extend later.
Who sets the expiry date on my batches?
You do, as the brand owner, based on the shelf life established for that formula and pack, counted from the manufacture date of each batch.
This article is general information, not legal advice. Check current requirements for your product type and markets.