How Long Does a 1% Methylene Blue Solution Last? Shelf Life & Stability
Mark Kemp · 22 June 2026
A 1% methylene blue solution is stable at room temperature: two years unopened, twelve months once opened, stored cool and out of light.
A 1% aqueous methylthioninium chloride solution is chemically stable at room temperature and does not require refrigeration; light is its main route of degradation, reducing it to a colourless leuco form, which is why it is kept in cobalt glass and out of direct light. Unopened, Blu Brain's solution has a two-year shelf life from the date of production, printed as a use-by date on every 30 ml box.
| Factor | Effect on the solution | Control |
|---|---|---|
| Light | Photoreduction to the colourless leuco form; the blue fades | Cobalt glass; store out of direct light |
| Heat | Accelerates degradation | Store 2–25 °C; never above 50 °C |
| Air | Oxidation alters the active compound | Keep tightly closed in the original bottle |
| Freezing | May affect the solution | Do not freeze |
Is a 1% methylene blue solution stable at room temperature?
Yes. A 1% (w/v) aqueous methylthioninium chloride solution is stable under normal storage conditions and needs no refrigeration. Blu Brain's solution is prepared in purified water with no added stabilisers; when stored cool, dry, and out of light, it maintains its specification throughout its shelf life. Unopened, that shelf life is two years from production, and every 30 ml box is printed with its use-by date — for batch 10023, produced 28 April 2025, that date is 28 April 2027. Once opened, use the solution within 12 months, stored as follows.
What degrades it — light, heat and air
Three things shorten the solution’s lifespan. Light is the main one: visible light reduces methylene blue to its colourless leuco form, so a fading of the deep blue is the clearest sign of photodegradation, which is why the solution is supplied in cobalt glass. Heat accelerates breakdown, so keep it at 2–25 °C and never above 50 °C. Air promotes oxidation, so keep the bottle tightly closed in its original container. Freezing should also be avoided.
How to store it and spot degradation
Store the bottle tightly closed in a cool, dry place between 2–25 °C, out of direct light and away from heat; do not freeze it. Inspect it from time to time: discard if the deep blue fades noticeably, if particulate or sediment appears, or if the seal is compromised. A clear, deep copper-blue liquid with no sediment is the solution in good condition.