A lotion can look unchanged after storage while its pump becomes harder to use. A useful stability study makes room for both observations, then gives the team a way to decide what they mean.
Before samples go into storage, define the study objective, identify the samples, and agree how changes will be measured and assessed.
Decide whether you are screening, comparing, or supporting shelf life
Early prototype screening, package comparison, and support for a proposed product life are different projects. State which one this study addresses. ISO/TR 18811 provides a framework for cosmetic stability work but does not prescribe universal conditions, parameters, or acceptance criteria; the manufacturer must justify the protocol for the product.1
For example, a hypothetical study might compare formula F-218 in two proposed pumps. Select samples and observations that can reveal differences between those packs. Assess the relevance to other packaging separately.
Cosmetics Europe’s guidance considers product and packaging together, discusses manufacturing scale, and recommends real-time follow-up to support predictions from accelerated work.2
Identify the units going into the study
Label each sample so it leads back to the formula version, prepared batch, package specification, storage condition, and planned assessment point. State any differences between the prototype and intended commercial product.
Work out quantities before starting. Some assessments consume or disturb a sample, so one repeatedly opened container may not serve every purpose. Record replacements, moves, and storage excursions against the affected units.
Define how a change will be measured
Select observations relevant to the product, potentially including appearance, odour, pH, viscosity, package condition, and appropriate analytical or microbiological measures.2 Define the method and acceptance basis for each. “Viscosity acceptable” needs a method, units, and criteria before it can be reviewed.
Take a baseline. Keep comparison conditions consistent, and explain changes to methods or instruments during the study. Set criteria before seeing the results; preserve the justification and earlier version if a criterion is subsequently revised.
| At each assessment | Record |
|---|---|
| Identity and timing | Sample reference, planned point and actual date |
| Storage history | Location, relevant conditions and excursions |
| Observation | Method, equipment, result and units |
| Supporting material | Original data or photograph reference |
| Responsibility | Observer and required review |
| Exception | What happened, its effect and follow-up |
“Not measured” and “no change observed” must remain distinguishable.
Investigate the package as well as the contents
If one pump in that comparison starts dispensing unevenly, record which unit failed and how. Record the condition of the lotion separately. Examine the pump and compare other units while retaining the original finding.
Apply the same approach to late assessments and storage excursions: identify the affected samples, assess the effect, and explain whether more work is needed.
State what the completed work supports
The report should summarise trends, deviations, remaining work, and the conclusion for the tested combination. Distinguish observations from predictions. A fixed short accelerated study does not have a universal conversion into years of shelf life.12 FDA also describes shelf life as dependent on product, use, and storage.3
Attach the protocol and results to the conclusion. Identify any follow-up still due, including the planned real-time assessments.
Sources
International Organization for Standardization. ISO/TR 18811:2018: Guidelines on the stability testing of cosmetic products. Public scope and available preview. ↩︎ ↩︎
Cosmetics Europe and CTFA. Guidelines on Stability Testing of Cosmetic Products, March 2004. Industry guidance published in March 2004. ↩︎ ↩︎ ↩︎
US Food and Drug Administration. Shelf Life and Expiration Dating of Cosmetics. ↩︎
