Store lyophilized (dry) peptides sealed, dark and frozen, at -20 °C or colder for long-term storage. Once reconstituted, peptides degrade much faster: keep solutions cold, split them into single-use aliquots, and avoid repeated freeze-thaw cycles. Let any cold vial reach room temperature before opening it, so moisture doesn't condense on the powder.
Notice: Research peptides are sold for in-vitro laboratory research only. They are not FDA-approved, not for human or animal consumption, and this page is not medical advice.
The guidance below comes from the published handling guides of three peptide manufacturers: Sigma-Aldrich, Bachem and GenScript. Where they differ, we say so. Always follow the storage note on your vial or COA if it is more specific.
Quick reference
| Form | Short term | Long term | Key risks |
|---|---|---|---|
| Lyophilized (dry) | 4 °C or colder on receipt; stable at room temperature for days to weeks | -20 °C, or -80 °C preferred | Moisture, light |
| Reconstituted (solution) | About 1 week at 4 °C (general figure) | Frozen aliquots at -20 °C or colder | Freeze-thaw, oxidation, microbial growth |
Sources: Sigma-Aldrich guide (PDF), Sigma-Aldrich technical article.
Storing lyophilized peptides
Temperature
- Sigma-Aldrich: for long-term storage, "–20 °C or preferably at –80 °C" (Sigma-Aldrich). On receipt, "store at 4°C or colder" (PDF guide).
- Bachem: "in a tightly closed container at less than −15 °C, although lower temperatures are preferred" (Bachem).
- GenScript: "Lyophilized peptides should be stored at -20℃, away from bright light" (GenScript).
The three agree: frozen is the standard for anything you won't use soon.
Shipping at room temperature
Research peptides often arrive without ice packs. That is consistent with Sigma-Aldrich's statement that "lyophilized peptides are stable at room temperature for days to weeks, but for longer-term storage, it is safer to store at -20 °C or colder" (PDF guide). Days to weeks is not months. Put vials in cold storage when they arrive. For transit times by vendor, see fastest shipping peptide vendors.
Moisture
Moisture is the main threat to a dry peptide. Sigma-Aldrich warns that "exposure to moisture will greatly decrease the long-term stability" (Sigma-Aldrich). Bachem notes that peptides are hygroscopic and advises that the container "be allowed to reach ambient temperature in a desiccator prior to opening" (Bachem).
GenScript adds that sequences containing Asp, Glu, Lys, Arg or His "are prone to moisture absorption from the air" and should be kept "in a dessicator in a tightly capped vial" (GenScript).
In practice: keep the cap on, store with a desiccant if you can, and never open a vial straight out of the freezer.
Light
All three guides say to store peptides away from bright light. An amber box or an opaque container in the freezer is enough.
Storing reconstituted peptides
Once dissolved, a peptide's clock speeds up. Sigma-Aldrich says "the shelf life of peptide solutions is limited" (Sigma-Aldrich).
Refrigerated
Sigma-Aldrich's general figure is that "peptide solutions are stable for up to a week at 4 °C" (Sigma-Aldrich). That is a rule of thumb, not a guarantee for any specific compound. Some sequences degrade faster.
Frozen
For longer storage, Sigma-Aldrich says "storage at –20 °C or colder is optimal" and that sterile buffers at pH 5 to 6 and frozen aliquots prolong storage life (PDF guide). Bachem recommends that "peptide solutions should be aliquoted and kept frozen below −15 °C," adding that frozen solutions "may be kept for a few weeks" and that extended storage calls for the lyophilized form (Bachem).
Sigma-Aldrich also says solutions at pH above 8 "should also be frozen when not in use."
Sequences that need extra care
Some amino acids make a peptide less stable:
| Residues | Problem | Source |
|---|---|---|
| Cys (C), Met (M), Trp (W) | Air oxidation | Sigma-Aldrich, Bachem |
| Asn (N), Gln (Q), Cys, Met, Trp | Unstable in solution; limited shelf life | Sigma-Aldrich, Bachem |
| Asp, Glu, Lys, Arg, His | Absorb moisture as a dry powder | GenScript |
Check the sequence on the COA. If it contains these residues, keep solutions for shorter periods.
Freeze-thaw cycles and aliquoting
Every source agrees on this one. Sigma-Aldrich: "Repeated freeze-thaw cycles should be avoided for both lyophilized peptides and peptide solutions" (Sigma-Aldrich). GenScript: peptides "that undergo freeze-thaw cycles are susceptible to degradation" (GenScript).
The fix is aliquoting: splitting a stock solution into several small tubes so you only thaw what you need. GenScript notes that aliquoting "reduces the number of freeze-thaw cycles, and reduces the amount of air exposure to the peptide."
A simple aliquoting workflow:
- Reconstitute the vial and record the concentration (calculator).
- Work out how much you need per experiment.
- Divide the stock into tubes of that volume.
- Label each tube with peptide, lot, concentration and date.
- Freeze all but the one you are using now.
- Thaw one tube at a time and don't refreeze leftovers.
If you used bacteriostatic water
Bacteriostatic water contains benzyl alcohol to limit microbial growth in a multi-use vial. CDC says an opened multi-dose vial should be discarded within 28 days unless the manufacturer states otherwise (CDC). That rule is about the diluent vial. It says nothing about how long a peptide stays stable once dissolved. See bacteriostatic water vs sterile water.
A storage checklist for when a vial arrives
- Check the package. Note if it arrived damaged, wet or unusually warm, and photograph anything odd before you open further.
- Inspect the cake through the glass. It should look like a dry solid, not a liquid or a sticky film.
- Match the lot number to the COA. Do this now, while the vendor's page and your order email are easy to find.
- Label the box with the arrival date. Room-temperature stability is measured in days to weeks, so the date matters.
- Move it to cold storage. Freeze anything you won't reconstitute soon; keep it sealed, dry and dark.
- Log it. Record peptide, lot, vial mass, arrival date and storage location in your notebook.
Signs a vial may be compromised
- The dry cake looks melted, shrunken or sticky before reconstitution (what that can mean).
- The solution is cloudy or has particles after it was clear.
- The vial was left warm for an unknown time.
- The label or storage date is missing.
None of these tells you exactly what went wrong. They are reasons to set the vial aside rather than trust it.
Storage can't fix a bad vial
Good storage preserves what is in the vial. It can't correct a mislabeled or low-purity product. Check a vendor's lot-level testing before you buy; see how to read a peptide COA and our ranking of the best place to buy peptides online, which is an editors' ranking, not a sort by score (how we rank).
For how long a vial keeps once water is added, see how long reconstituted peptides last.
Sources are linked inline. Last reviewed September 26, 2026.