Temperature and degradation

The rough rule

Reaction rates increase with temperature — as a rough guide, many degradation reactions roughly double in rate for each 10 °C rise. The corollary is more useful: each step down in storage temperature buys a disproportionate amount of stability.

This is why the same peptide is quoted with quite different shelf lives at room temperature, at refrigerator temperature and frozen.

Excursions are cumulative

Time above the intended temperature accumulates. An hour on a bench is negligible; a week is not. Degradation does not reverse when the vial goes back in the fridge — the damage already done is permanent.

This is why an expiry date describes material stored as specified. A vial that has spent a month at ambient temperature has not been.

Dry versus dissolved

Lyophilized material tolerates excursions far better than solution, because the reactions needing water are suppressed. The same excursion that is trivial for a dry vial can be significant for a reconstituted one.