What changes force a retest

A challenge test certifies one formula, in one package, made one way. The useful question is what breaks that certification, and the answer is a longer list than most brands act on.

The rule

If it changes the preservation system, retest. The preservation system is water activity, preservative blend, pH, chelators and the package, so anything touching those is in scope.

Changes that always force it

A different preservative, obviously, or a different level of it. A change in pH, because preservatives have ranges in which they are active and outside which they are present but useless. A new package, especially from a jar to a pump or the reverse. A change in water content or anything that moves water activity.

And a new raw material supplier for anything in the water phase, because trace impurities, different water content and different particle size can all move pH, emulsion behavior or preservative efficacy in ways that pass an initial quality check and surface later.

Changes people wrongly think are safe

Fragrance. It is usually oil soluble and frequently interacts with the emulsifier and the preservative.

Color. Same reasoning, and some pigments carry metal ions that consume chelator.

Scaling the batch. Mixing energy, cooling rate and time at temperature all change, and all affect the emulsion the preservation is protecting.

A botanical extract swap. Extracts carry their own microbial load and their own preservative demand.

Building it into the process

Write the certified configuration down: formula version, package, pH range, and the date and laboratory of the test. Attach it to the product record rather than filing it separately.

Then make a retest a required step in any change, the way a reformulation is. The failure mode is not a brand deciding to skip a test; it is a brand making four small changes over two years and never noticing that the tested configuration no longer exists.

References