You have a formula that passed its preservation test, and now you are choosing between a jar, a pump bottle and a tube. Does the pack matter? Questions about challenge test packaging come up in almost every launch, because the formula and its container reach the consumer together. This guide explains what a challenge test does and does not tell you about packaging, how pumps, jars and tubes differ, and when it is sensible to test again.
Contents
- The short answer
- What a challenge test actually measures
- How packaging influences preservation in real life
- Jars, pumps, airless pumps and tubes compared
- When a new pack means a new test
- What to test: product, pack, or both
- Common mistakes with packaging and challenge tests
- What goes into the CPSR and the product file
- A short checklist before you order
- Frequently asked questions
- Key takeaways
The short answer
A challenge test mainly evaluates the formula and its preservation system, not the container, so a pass does not automatically cover every pack. Packaging can still change the real-life outcome: it decides how much contamination gets in during use, and some materials can absorb or react with preservatives. When you change the pack material or the dispensing type, ask your safety assessor whether the existing result still applies, and consider repeating the test or adding a stability check in the new pack. There is no universal rule, so the decision should be documented rather than assumed.
What a challenge test actually measures
In a preservation efficacy test, the laboratory deliberately adds five reference microorganisms to the product and counts how many survive over 28 days. The result shows whether the preservative system can cope with the contamination load defined by the standard, such as ISO 11930:2019 or USP 51. It is a test of chemistry and formulation under controlled conditions.
Depending on the laboratory and protocol, the product is often inoculated in suitable test containers rather than in the finished pack, because the finished pack would have to be opened, filled with microorganisms and resealed. That is why the result is best read as “this formula is adequately preserved” and not as “this formula is adequately preserved in every container on the market”. Check your report to see exactly what container was used.
Read also What Is a Cosmetic Challenge Test? Preservative Efficacy Testing Explained
How packaging influences preservation in real life
Packaging affects the microbiological life of a product in four main ways:
- Exposure during use. A wide opening that fingers and spatulas touch brings in far more microorganisms than a closed dispensing system.
- Preservative loss. Some plastics and liners can absorb part of a preservative or fragrance, and some closures and seals can interact with the formula. This lowers the effective concentration over time.
- Changes in the formula. Water loss, oxygen and light can shift pH, texture or colour, which can in turn change how well preservatives work.
- Filling and closing. Residues, humidity and handling in the filling line can introduce contamination before the product reaches the consumer.
Standards such as ISO 11930 and ISO 29621 treat antimicrobial protection as the combined effect of formula, packaging, use and manufacturing, which is why packaging belongs in the safety discussion and not only in the design brief.
Jars, pumps, airless pumps and tubes compared
The comparison below is about relative risk, not a guarantee. A well-preserved formula can be fine in any of these, and a poorly preserved one can fail in all of them.
- Jars. Open access, fingers and tools. This is usually the most demanding pack for preservation and the one where a robust challenge test matters most.
- Pump bottles. Less direct contact, but the nozzle can stay wet and some pumps can draw air or residue back after dispensing. Preservative adsorption on the pump parts is worth checking.
- Airless pumps. Designed to limit air and backflow, which usually lowers the exposure. They do not replace preservation, because contamination can still enter at filling or at the nozzle.
- Tubes. The small orifice limits contact, though residue at the tip and the sealed end can be a factor. Metal and laminate tubes can have internal coatings that matter for compatibility.
- Droppers and pipette bottles. The dropper is repeatedly dipped in and out of the product and touches skin or eyes, so they are generally treated as demanding.
Treat “airless” or “sealed tube” as a risk-reduction measure and ask your assessor how much credit it deserves in your specific case.
When a new pack means a new test
Changing the formula normally calls for a new test. Changing only the pack is a judgement call. These situations usually deserve a conversation with your assessor:
- A different material, for example glass to plastic, or one polymer to another, especially when the formula contains preservatives known to interact with plastics.
- A different dispensing type, such as jar to pump, tube to dropper or standard pump to airless, in either direction.
- A different supplier or a new liner, seal or closure, because the contact materials may not be identical.
- A much larger or smaller fill volume, which changes headspace and use pattern.
- A move into a higher-risk use, such as an eye-area product or one for babies.
If the assessor concludes that a repeat test is not needed, write down why. If in doubt, a repeat challenge test on the new pack is usually the simplest way to remove the doubt.
Read also Challenge Test Cost: What Affects the Price
What to test: product, pack, or both
The challenge test answers one question, the stability and compatibility study answers another. A practical set looks like this:
- Challenge test on the final formula with the final preservative system.
- Stability and compatibility testing in the final pack, to see whether the pack changes the formula or the preservative level over the shelf life.
- Microbiological specifications on the filled product, to confirm that it leaves your line clean.
Some brands also run the challenge test on aged samples taken from the final pack near the end of the planned shelf life. This is optional practice, not a requirement, but it checks preservative performance when it is most likely to be reduced.
Common mistakes with packaging and challenge tests
- Testing the formula in a laboratory container and selling it in a different pack without any further consideration.
- Assuming an airless pump allows you to reduce the preservative system.
- Sending prototype packs that differ from the final ones, such as another material, closure or liner.
- Ignoring the consumer’s behaviour: a jar kept in a humid bathroom is not the same as a sealed tube in a drawer.
- Forgetting that refill, sample or travel sizes are separate packs with their own contact materials.
What goes into the CPSR and the product file
The EU Cosmetics Regulation (EC) No 1223/2009 requires the safety information in the product information file to cover the microbiological quality of the product and relevant characteristics of the packaging material, in particular its purity and stability. Challenge test data is usually included where relevant. A safety assessor therefore expects a clear link between the pack you will actually sell and the evidence you present. Our CPSR service looks at the formula, the data and the packaging information together.
Read also My Product Failed the Challenge Test: What to Do Next
A short checklist before you order
- Write down the final formula, preservative system and pack, including material, closure and liner.
- Note any later pack options you are considering.
- Ask your assessor which pack the result must cover.
- Choose the standard, usually ISO 11930:2019 or USP 51.
- Send finished product, ideally in the final pack, so the laboratory can choose the right test container.
Frequently asked questions
Do I need a separate challenge test for every pack size?
Not automatically. If the pack is made of the same material, has the same dispensing type and the formula is identical, many assessors accept one result for several sizes. Document the reasoning, and test again if the contact materials or dispensing type differ.
Does an airless pump or a sealed tube replace preservatives?
Generally not. Such packs reduce exposure during use, but contamination can still happen at filling, and the product is exposed once opened. Whether a reduced preservative system is acceptable is a risk assessment decision for your safety assessor and has to be supported by data.
Can packaging make a passing product fail?
It can in some cases, for example if a material absorbs a share of the preservative. A stability and compatibility study in the final pack helps to detect this before launch.
Key takeaways
- A challenge test mainly evaluates the formula and its preservation system, not every pack on the market.
- Jars, pumps, airless pumps and tubes expose the product to different amounts of contamination during use.
- A change of pack material or dispensing type should be assessed by your safety assessor, and the decision documented.
- Combine the challenge test with stability and compatibility testing in the final pack for the strongest evidence.