Did you know chlorine bleach has a shelf life? Whether the container has been opened or not, bleach loses its activity over time. Using bleach past its shelf life results in reduced bleaching and disinfecting capacity.
How Long Is Bleach Good?
How long bleach lasts depends mainly on temperature. So, Clorox™ adds a different amount of hypochlorite to bleach depending on the season when it is manufactured. Bleach manufactured and sold in summer starts out with more hypochlorite than bleach manufactured and sold in winter. Clorox adjusts the composition of its products so the bleach maintains a 6% sodium hypochlorite concentration for at least six months after the manufacturing date. It takes around 4 to 8 weeks for chlorine bleach to make it from the manufacturer to the store shelf, so bleach maintains peak effectiveness for about 3 to 5 months after its purchase date.
Bleach shelf life is affected by temperature. Bleach should be stored at room temperature or cooler (around 70°F). If it is stored in a warmer location (like a hot garage, around 90°F), it is effective about 3 months. At room temperature, it maintains 6% hypochlorite about 5 months after purchase.
Does this mean you need to replace bleach every 5 months? Not necessarily. Bleach at 6% hypochlorite level is the EPA disinfection standard. If you are using bleach as a disinfectant, it’s a good idea to replace it at least once every six months. On the other hand, if you are using the product to bleach clothes or surfaces, you can expect good results for about 9 months. Clorox recommends replacing bleach at least once a year. It’s reasonable to expect chlorine bleach made by other manufacturers has about the same shelf life.
What Does Bleach Turn Into?
The active ingredient in chlorine bleach is sodium hypochlorite (NaOCl), although at a low pH value, it also contains hypochlorous acid. Sodium hypochlorite decomposes via two mechanisms. One is into sodium chlorate and salt (sodium chloride), while the other is into oxygen and salt:
3 NaOCl → NaClO3 + 2 NaCl
2 NaOCl → O2 + 2 NaCl
The first reaction is the primary decomposition mode. It is affected by temperature and concentration. The second reaction is catalyzed by light and the presence of trace amounts of metals. Over time, sodium chlorate also decomposes, so a bottle of bleach becomes a bottle of salt water.
How to Tell When Bleach Has Expired
One way to tell whether or not bleach is effective is to smell it. No, don’t open the bottle and take a whiff! You could get a chemical burn. Instead, pour the bleach from its container. The human nose is highly sensitive to the odor of chlorine, so if you smell it as soon as you pour the bleach, it still has some activity. On the other hand, if you don’t smell bleach it has probably decomposed into salt and water. It’s time to replace it with a fresh bottle.
How to Maximize Bleach Shelf Life
The factors that affect bleach shelf life are temperature, exposure to light, the presence of contaminants like metals, the pH of the solution, and the initial hypochlorite concentration. Knowing this, here are the steps to take to maximize bleach shelf life:
- Store bleach at room temperature and not in a place where it will experience freezing or hot conditions. Usually, this means bleach should be stored indoors rather than a garage or storage shed. Be sure to store it away from access by children or pets.
- Keep the bleach in its original container. This container is opaque, so it minimizes any reaction with light. Using the original container also minimizes the risk of contamination.
- Keep the cap tightly sealed on the container.
References
- Oxy Occidental Chemical Corportation (2014). OxyChem Sodium Hypochlorite Handbook.
- Robertson, G.L. (2010). Food Packaging and Shelf Life: A Practical Guide. CRC Press. ISBN 978-1-4200-7844-2.
- Soroka, W. (2002). Fundamentals of Packaging Technology. Institute of Packaging Professionals. ISBN 1-930268-25-4.
- The Chlorine Institute (September 2017). Pamphlet 96: Sodium Hypochlorite Manual.