Light
Light, especially ultraviolet, carries enough energy to start chemical reactions. In peptides and proteins the amino acids that undergo primary photo-oxidation include tryptophan, tyrosine, phenylalanine and cysteine/cystine. The products can differ in structure from the original molecule.
Regulators treat this seriously. ICH guideline Q1B sets out photostability testing to show whether light exposure causes unacceptable change, and stress testing under ICH Q1A includes photolysis.
Moisture
Freeze-dried powder is not free of reactions. A review of solid-state stability lists deamidation, peptide bond cleavage, oxidation, dimerisation and aggregation as reactions that can occur in dry peptides, and names moisture content and temperature as key factors that influence them.
That is why stability testing records the moisture level of powders and freeze-dried products, and why stress testing uses high humidity (75% relative humidity or more).
Containers do much of the work
ICH guidance notes that these products are usually supplied in containers that protect against humidity, and that labelling should state any need for protection from light or humidity. Keeping a vial sealed, dry and away from light follows the same logic.
For how long a particular material stays stable, the manufacturer's or the lab's own data is the guide. Research peptides are for laboratory research only and are not approved medicines.
Educational information only. Nothing here is medical advice, dosing guidance or a recommendation to use any substance. Research peptides are not approved medicines and are not for human or animal consumption. Speak to a qualified professional and follow the law where you are.
