Does bleach go bad, and how long does diluted bleach last?

Yes. Bleach does not spoil, but it loses strength from the day it is made, faster when it is warm, exposed to light, or diluted in an open or clear bottle. For diluted bleach, follow CDC: make a new solution every day, because bleach solutions "will not be as effective after being mixed with water for over 24 hours." For the bottle as sold, the only manufacturer figure found is old: in 2003 Clorox told Weill Cornell's safety office that its bleach kept for about 6 months at 50 to 70°F and then lost about 20 percent a year. Two laboratory studies found diluted bleach lasting far longer in the right container; below is why this page still follows CDC.

Diluted bleach: what the sources say

For scale: CDC's dilution of 1/3 cup of bleach per gallon of water is roughly 1 part bleach to 48 parts water (our arithmetic: 1/3 cup is about 2.7 fluid ounces, a gallon is 128), close to Rutala's 1:50. The full CDC method is on making a bleach disinfecting solution.

Why this page follows CDC anyway

The studies and CDC disagree, and both studies say so directly: Rutala's authors concluded that chlorine solutions "do not need to be prepared fresh daily, as is recommended currently" [3], and Gow's concluded solutions "can be prepared on a weekly, biweekly, or monthly basis" [4]. This page follows CDC's daily rule for home use, for four reasons:

1. Container decides the result. Rutala's diluted bleach kept nearly all its chlorine only in closed brown containers; in the others, half was gone in a month [3]. A kitchen spray bottle is rarely a closed brown container.
2. The studies measured; you cannot. Gow's team checked chlorine with a spectrophotometer and test strips [4]. At home you have no way to know whether yesterday's bottle is at 100 or 50 percent.
3. The studies were narrow. Gow tested one bleach brand at one starting strength, with three bottles per group, and did not test germ killing [4].
4. CDC is the federal public health source and its daily rule needs no equipment.

If you work in a facility with a written protocol and a way to test chlorine, the studies show a longer interval can be justified there. That decision belongs in the facility's own written procedure.

Undiluted bleach in the bottle

The only manufacturer statement found on bottle shelf life is the 2003 Clorox reply quoted by Weill Cornell Medicine's Environmental Health and Safety office [2]:

• The bottle carries "no expiration date, only a production date."
• It keeps "about 6 months at temperatures between 50 and 70 degrees Fahrenheit."
• After that it degrades at about 20 percent a year "until it becomes salt and water."
• Storing it well above 70°F reduces effectiveness and speeds the breakdown.

That reply concerned Clorox's 2003 "Ultra" bleach. The product may have changed since, and no current Clorox shelf-life statement was reached for this page, so treat the figures as a dated manufacturer estimate. Clorox's current SDS gives its regular bleach as 5 to 10 percent sodium hypochlorite, says to "Keep containers tightly closed in a dry, cool and well-ventilated place," and lists "Exposure to air or moisture over prolonged periods" as a condition to avoid [5].

One real-world data point: Gow's team bought a bleach product they expected to be 6 percent and found it was 4.5 percent when they tested it [4]. The paper does not say how old the bottle was. It shows that the strength on a shelf can be well below what you assume.

What speeds the breakdown

What the gas does to people is covered on bleach and vinegar.

Reading the date on the bottle

Clorox's 2003 reply says the bottle shows a production date rather than an expiry date [2]. How to read the code is not explained in any source reached for this page. If you cannot read it, call the consumer number on the label, or write the purchase date on the bottle when you bring it home. A bottle bought in summer and kept in a hot garage is the one most likely to have lost strength.

What to do with old bleach

• For disinfecting, CDC tells you not to use a bleach product "if the percentage is not in this range or is not specified" [1]. An old bottle's real strength is unknown, so for jobs where germ killing matters, buy a fresh bottle with the percentage and an EPA registration number on the label.
• For laundry or general cleaning, an older bottle still works, more weakly. The dose on the label assumes full strength.
• To get rid of it, NMSU says to flush leftover bleach "down the toilet or a drain followed with plenty of water" and to rinse the container before recycling [7]; Clorox's SDS says to dispose of it according to federal, state and local rules [5]. Never pour it into a drain where you have just used an acid cleaner or ammonia. Getting rid of old cleaners covers local rules and septic systems.

Keeping the next bottle at full strength

Buy a size you will finish well inside the roughly 6 months Clorox gave in 2003, store it cool and closed in its own bottle, away from acids and ammonia, and mix dilutions fresh each day. Where to put it is on storing cleaners at home.

References

1. Centers for Disease Control and Prevention, *Cleaning and Disinfecting with Bleach*, last reviewed April 24, 2024. https://www.cdc.gov/hygiene/about/cleaning-and-disinfecting-with-bleach.html
2. Weill Cornell Medicine, Environmental Health and Safety, *How Long Does Diluted Bleach Last?* (FAQ quoting a February 6, 2003 reply from Clorox consumer services), read October 2026. https://ehs.weill.cornell.edu/faq/how-long-does-diluted-bleach-last
3. Rutala W.A., Cole E.C., Thomann C.A., Weber D.J., *Stability and Bactericidal Activity of Chlorine Solutions*, Infection Control and Hospital Epidemiology 1998;19(5):323-327, doi:10.1086/647822 (abstract read). https://www.cambridge.org/core/journals/infection-control-and-hospital-epidemiology/article/abs/stability-and-bactericidal-activity-of-chlorine-solutions/49E6D38F740178FA86A8D8EF23103CFB
4. Gow C.K., Weinhouse C., O'Brien Johnson G., Saunders K.E., *Stability of Free Available Chlorine Levels in Dilute Sodium Hypochlorite Solutions over a 6-Week Period*, Journal of the American Association for Laboratory Animal Science 2022;61(2):181-187, doi:10.30802/AALAS-JAALAS-21-000080. https://aalas.kglmeridian.com/downloadpdf/view/journals/72010024/61/2/article-p181.pdf
5. The Clorox Company, *Safety Data Sheet: Clorox Regular Bleach2*, revised December 9, 2020. https://www.thecloroxcompany.com/wp-content/uploads/2020/12/US001153-Clorox-Regular-Bleach2_3.pdf
6. Olin Chlor Alkali, *Sodium Hypochlorite: Properties and Hazards Information* (Sodium Hypochlorite Safe Handling), April 2025 upload, read October 2026. https://olinchloralkali.com/wp-content/uploads/2025/04/Olin-Sodium-Hypochlorite-Safe-Handling.pdf
7. New Mexico State University Cooperative Extension Service (revised by Rick Griffiths and Sonja Koukel), *Green Alternatives to Toxic Household Products and Hazardous Waste*, G-313, revised February 2019. https://pubs.nmsu.edu/_g/G313/index.html