Like many household chemicals, hydrogen peroxide (H2O2) has a shelf life. Over time, peroxide breaks down into water and oxygen. The shelf life of a bottle of unopened household peroxide is about 3 years, while it’s only good for 1 to 6 months after the seal is broken. Household peroxide is between 3% and 7% hydrogen peroxide in water. More concentrated peroxide solutions, such as the 30% and 35% peroxide used in labs and for hair developer, degrade more quickly. For these solutions, the shelf life is about 1 year unopened, but only 30 to 45 days after opening for peak effectiveness.
Factors That Affect Peroxide Shelf Life
Hydrogen peroxide is inherently unstable, so it degrades no matter what. However, the rate of decomposition depends on several factors. Light has the greatest effect on peroxide, which is why peroxide comes in brown or opaque white bottles. Temperature also affects how long peroxide lasts. Higher temperatures increase the rate of decomposition, while lower temperatures slow down the reaction. The third factor that impacts peroxide shelf life is pH. So, manufacturers include a stabilizer and adjust the pH of household peroxide so it’s slightly acidic. More concentrated solutions typically don’t include stabilizers, but the main reason they decompose more quickly is simply because the rate of decomposition increases with concentration. In other words, the more concentrated a peroxide solution is, the shorter its shelf life. Exposure to other chemicals may also increase peroxide degradation. Opening a bottle of peroxide exposes it to oxygen in air, which hastens the decomposition reaction.
An unopened bottle of 3% hydrogen peroxide solution decomposes at the rate of about 0.5% per year. The product tends to be bottled at a slightly higher concentration than what you see on the label to account for the time between bottling and purchase. Research indicates a sealed bottle of 4% hydrogen peroxide decomposes from 4.2% to 3.87% within three years, while a 7.5% solution degrades from 7.57% to 7.23% in three years.
How to Extend Hydrogen Peroxide Shelf Life
You can extend the shelf life of hydrogen peroxide solution by keeping it in its original dark-colored or opaque bottle and storing it in a dark, cool location. Refrigeration helps, especially for concentrated solutions.
Test Peroxide to See If It’s Still Good
It’s easy to test household hydrogen peroxide to see if it’s still good. Pour a bit into a sink. If it bubbles, the peroxide is still active. If no bubbles are seen, the liquid has turned into water and it’s time to get a fresh bottle.
Why Peroxide Bubbles
Hydrogen peroxide decomposes into water and oxygen, even in a sealed bottle. The chemical equation for the reaction is:
2 H2O2 → 2 H2O + O2(g)
In the bottle, the reaction is slow, but when you pour hydrogen peroxide onto a cut, it proceeds quickly. The bubbles that appear are oxygen gas. The reason a cut bubbles from peroxide is because blood contains hemoglobin, which in turn contains iron, and it also contains the enzyme catalase. Iron and catalase both catalyze the decomposition of peroxide.
2 H2O2 → 2 H2O + O2(g)
In the bottle, the reaction is slow, but when you pour hydrogen peroxide onto a cut, it proceeds quickly. The bubbles that appear are oxygen gas. The reason a cut bubbles from peroxide is because blood contains hemoglobin, which in turn contains iron, and it also contains the enzyme catalase. Iron and catalase both catalyze the decomposition of peroxide.
In fact, cells contain catalase to protect tissues from attack by peroxide. Cells naturally produce peroxide, which could cause oxidative damage. Catalase inactivates peroxide before it can do much harm.
While the activity of hydrogen peroxide makes it a great disinfectant, it’s actually not ideal for treating wounds because it kills healthy cells along with pathogens. Some studies indicate peroxide may inhibit healing and increase the likelihood of scar formation.
References
- Brauer, Georg. (ed.) (1963). Handbook of Preparative Inorganic Chemistry. 1. Translation editing by Reed F. (2nd ed.). New York, N.Y.: Academic Press. ISBN 978-0-12-126601-1.
- Postlewaite, J.; Taraban, L. (2015). “A Study Monitoring the Hydrogen Peroxide Stability for Shelf-Life Determination Using a Permanganate Titrate Test Method.” Technotes by Texwipe Vol. XIV, No. 9.
- PubChem (2004). “Hydrogen Peroxide.” U.S. National Library of Medicine: National Center for Biotechnology Information.
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