Cosmetic stability testing: requirements, test plan and documentation

The obligation follows from Article 10 and Annex I. Part A, point 2 of the Annex lists, for the safety report, the physical and chemical characteristics of the substances or mixtures and of the cosmetic product, and the stability of the cosmetic product under reasonably foreseeable storage conditions. Part A, point 4 adds the relevant characteristics of the packaging material, in particular purity and stability.

The Regulation sets no temperatures, durations or acceptance criteria. It requires an assessment that fits the product and can be followed in the safety report.

The guidelines on Annex I (Implementing Decision 2013/674/EU) state the purpose: to assess whether stability affects the safety and quality of the product, and to use that information to determine the minimum durability and the period after opening.

The safety report should therefore contain the method used to determine minimum durability, all data used to justify the indicated durability, and the description and results of the tests. In addition: evidence that the composition of the tested product corresponds to the product actually placed on the market, the results of a challenge test where applicable, and the period after opening with its justification where applicable.

The guidelines quote the Scientific Committee on Consumer Safety (SCCS): stability tests should be adapted to the type of product and its intended use. To make sure the packaging causes no stability problems, physical stability tests are carried out with inert containers and with those intended to be used on the market.

Substances can also migrate from the packaging into the formula, which is why information on the packaging material is part of the assessment. A change of packaging supplier or material is a reason to reassess the data.

Article 19(1)(c) governs the label. Where minimum durability is 30 months or less, the date is given with “best used before the end of” or the symbol in Annex VII, as month and year or day, month and year, supplemented by storage conditions where necessary. Above 30 months the date is not mandatory; instead the label states how long the product can be used safely after opening.

Both particulars rest on the stability data. Whoever prints a date or a period after opening must be able to show in the safety report where it comes from.

A test plan defines which samples are tested under which conditions at which time points, and which characteristics are measured or observed. Typical characteristics are appearance, colour, odour, pH, viscosity and phase separation, as well as changes to the packaging. Which conditions make sense depends on the product, the packaging and the markets.

Guidance comes from the technical report ISO/TR 18811:2018. It expressly does not specify conditions, parameters or criteria; it reviews literature on stability assessment and covers, among other things, batch scale, test conditions, physical and chemical changes, microbiological aspects, packaging interaction and evaluation. Defining and justifying the protocol remains the manufacturer’s task.

In practice this requirement of the guidelines is the trickiest. Stability studies run for weeks or months, and the formula is often still being adjusted during that time. It then quickly becomes unclear which version was in the climate chamber and whether the results still apply to the product going to market.

Every sample should therefore be linked unambiguously to the formula version, the production batch and the packaging. If the formula changes afterwards, a professional judgement is needed on whether the existing data can be carried over.

Stability testing looks at whether the product keeps its physical, chemical and sensory properties. The preservation challenge test checks whether the preservation system controls a microbial challenge. Both results feed into the justification of shelf life, but they are separate tests with their own methods.

In VYVA the formula carries the product specification: target pH, viscosity range, appearance, colour and odour. These targets appear in the test protocols next to the measured values instead of being retyped in every protocol. A test protocol belongs to a formula and a batch number and has its own sections for stability, climate stress, packaging compatibility, storage conditions, sensory evaluation and microbiology, plus a summary with approval. Photos and reports hang off the test.

This keeps visible which formula and batch were tested, what was measured and which decision followed. The professional judgement remains with people, the safety assessment with the qualified person.