Preservative efficacy testing — also called challenge testing or PET — deliberately contaminates your cosmetic product with five specified microorganisms to prove the preservative system can kill them. In New Zealand and Australia it is tested to ISO 11930, takes 28 days, and costs from NZ$1,200 per formula.
It is one of the least glamorous line items in an indie beauty launch, and one of the most consequential. A formula that separates is embarrassing. A formula that grows Pseudomonas in a customer's bathroom is a recall.
What is preservative efficacy testing in cosmetics?
A challenge test inoculates your finished product with a high concentration of microorganisms and then measures, at set intervals, whether the preservative system reduces them. Under ISO 11930 the standard panel is:
- Escherichia coli — a faecal indicator organism
- Staphylococcus aureus — a common skin bacterium
- Pseudomonas aeruginosa — the water-loving bacterium that causes most cosmetic recalls
- Candida albicans — a yeast
- Aspergillus brasiliensis — a mould
Counts are taken at days 7, 14 and 28. The test asks a simple question: if a consumer dips a finger into this jar, does the product defend itself?
What counts as a pass under ISO 11930?
ISO 11930 sets two acceptance levels. Criteria A is the standard target: bacteria must show at least a 3-log reduction (99.9%) by day 7 and no regrowth through day 28, while yeast and mould must show at least a 1-log reduction with no increase thereafter.
Criteria B is a lower bar, permitted only where a documented safety assessment justifies it — for example, a formula where a stronger preservative load would create an unacceptable irritation risk. Criteria B is not a consolation prize you claim after failing Criteria A. It has to be reasoned in advance by a safety assessor and defended in your product information file.
Challenge testing is distinct from ISO 17516, which sets microbiological limits for the product as manufactured. One proves your preservative works over time; the other proves your batch was clean on the day it was made.
Does every product need a challenge test?
Not every one — but more than most founders expect. As a working rule:
- Always test: anything containing water. Creams, lotions, serums, gels, toners, cleansers, sheet mask essences, micellar waters.
- Usually test: anhydrous products packed in jars or likely to be used with wet hands — sugar scrubs, balms in open pots, cleansing balms.
- Often exempt: genuinely anhydrous, low-water-activity products — facial oils, waxy sticks, dry powders. This should be documented as a reasoned exemption, not assumed.
What do New Zealand and Australian rules require?
Neither market mandates a challenge test by name, but both make it very difficult to defend a product without one.
In New Zealand, cosmetics fall under the EPA's Cosmetic Products Group Standard, which was updated effective 1 January 2026 — tightening ingredient restrictions and lowering maximum concentrations for several preservatives. If your formula was preserved to older limits, the balance may need revisiting. The Group Standard requires products to be safe in normal and reasonably foreseeable use; microbiological safety is part of that duty.
In Australia, cosmetic ingredients are regulated through AICIS, which governs what you may put in the product rather than how you prove it stays safe. Consumer safety obligations under Australian Consumer Law fill the gap. In practice, retailers, insurers and contract manufacturers ask for challenge test data long before a regulator does.
For EU and UK markets a challenge test is effectively non-negotiable — your Safety Assessor will require it before signing the Cosmetic Product Safety Report.
How much does preservative efficacy testing cost and how long does it take?
Budget from NZ$1,200 per formula, and around four to five weeks from sample dispatch to report — the 28-day protocol plus handling. Costs rise if you test multiple pack formats or need a repeat after reformulating.
A realistic sequencing looks like this: complete your formula, run challenge testing and 12-week accelerated stability in parallel from the same batch, review both, adjust if needed, then commit to production packaging and your first manufacturing run. Building a single testing round into the schedule from the start is far cheaper than discovering a failure after you have paid for 500 units of filled stock.
What happens if a formula fails?
Failure is common on a first pass and is not a disaster — it is the test doing its job. Typical causes and fixes:
- pH drift. Many preservatives only work within a narrow pH band. Organic acids such as sodium benzoate and potassium sorbate lose most of their activity above roughly pH 5.5.
- Preservative binding. Non-ionic surfactants, high-oil emulsions and some polymers sequester preservative into the oil phase where microbes are not.
- Botanical load. Plant extracts, hydrosols and aloe bring their own bioburden and often their own nutrients. Natural and organic formulas usually need a more carefully engineered system, not simply a "gentler" one.
- Insufficient boosters. Chelators such as sodium phytate, and multifunctionals such as glyceryl caprylate or 1,2-hexanediol, materially improve performance without adding to the preservative declaration.
Most failures resolve with a pH correction, a chelator, or a rebalanced multifunctional blend — followed by a retest of the corrected batch.
How The INCI Lab handles this
Every water-containing formula we develop goes through preservative efficacy and stability testing before it is released for manufacturing. We coordinate accredited lab testing, interpret the report, and — if it fails — reformulate and retest as part of the development process, not as a surprise invoice.
Both development pathways include this work. The Accelerator (4–6 months, starting from $2,000) fast-tracks a semi-custom formula to launch. The Visionary (9–12 months, starting from $4,000) develops a bespoke formula with full IP transferred to you before manufacturing begins.
If you already have a formula and want to know whether it will survive a challenge test before you spend the money, Ask The Chemist is a 30-minute consult for $150.
Frequently asked questions
Is preservative efficacy testing legally required in New Zealand?
Not by name. The EPA's Cosmetic Products Group Standard requires cosmetics to be safe in normal and reasonably foreseeable use, and microbiological safety is part of that. A challenge test is the accepted evidence that you have met the obligation, and retailers and insurers routinely ask for it.
Do I need a challenge test for an Australian launch?
AICIS regulates cosmetic ingredients rather than testing protocols, so there is no explicit AICIS requirement. Your general safety obligations under Australian Consumer Law still apply, and most Australian retailers and contract manufacturers request ISO 11930 data before stocking or filling a product.
How long does a challenge test take?
The ISO 11930 protocol runs 28 days, so expect roughly four to five weeks from sending samples to receiving the report. Run it alongside 12-week accelerated stability testing rather than after it.
How much does preservative efficacy testing cost?
From NZ$1,200 per formula. That covers one formula in one pack format — testing additional packaging presentations, or retesting after a reformulation, is charged separately.
Can a preservative-free product pass?
Only if it is genuinely anhydrous or water-activity controlled — an oil, a wax stick, a dry powder. Any product containing water needs an antimicrobial system. "Preservative-free" marketing claims usually rest on multifunctional ingredients that are not classified as preservatives but still perform that function.
Does a natural or organic formula make passing harder?
Generally yes. Botanical extracts add bioburden and nutrients, and the approved natural preservative palette is narrower and more pH-sensitive. It is entirely achievable — it needs a system designed for it from the outset rather than added at the end.
If I change my packaging, do I need to retest?
Yes. Challenge test results are specific to the formula and the pack. Moving from an airless pump to an open jar changes the contamination risk profile, and the original report no longer supports the new presentation.
Next step
If you are planning a launch in New Zealand or Australia and want the microbiological side handled properly from the first batch, get in touch or explore our formulation pathways. We will tell you honestly what your formula needs — and what it does not.
