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The Bleach Niche

Is the old standby, sodium hypochlorite, still the gold standard?

by Nancy Lawson

Reach for the bleach—that’s the first thing most shelters do when facing an outbreak, and the instinct is not unfounded. Sodium hypochlorite is still the biggest bang for your buck, and it’s still the best tried-and-true solution in shelter disease control.

“Hypochlorite is really still the kind of gold standard that people are using,” says Colin Parrish, a Cornell University virologist who studies parvoviruses. “The big problem is that it’s corrosive on steel and metal. ... Chlorine isn’t that great either in terms of breathing it, except that we’re all used to that.”

Though bleach may be the closest thing to disinfection’s golden child, its reputation is a bit tarnished by its bad-boy qualities—qualities that might make you think twice before you pledge your undying allegiance to it. Chris Quinlan of Animal Health Technology thought about it for years, in fact, before finally breaching his ban on bleach and deciding to sell a sodium hypochlorite product.

“If you asked me two years ago, we wouldn’t even sell bleach,” he says. “We do now.”

It was veterinarian Kate Hurley, director of the Maddie’s Shelter Medicine Program at the University of California, Davis, who convinced Quinlan of the benefits of bleach. It’s not just one of the only parvovirus inactivators; it’s also important in URI control. In fact, bleach played a critical role in helping to quell severe calicivirus outbreaks among rescue cats at several veterinary clinics, says Hurley, who investigated the cases.

“Because calicivirus is really significant in cats and the quats don’t reliably inactivate it,” she says, “I tend to recommend using bleach, depending on the level of turnover in cats, on a routine basis—daily in a place with high cat turnover, maybe less often in a place with low cat turnover.”

While still not charmed by the wonders of bleach, Quinlan has conceded—in light of the evidence—that it may be one of the only user-friendly products that’s effective against even the most curmudgeonly and intractable germs a shelter is likely to encounter.

But, he advises, the merits of bleach could be eroded by its pitfalls if not used properly. What follows is a discussion of three common mistakes bleach users make—and how you can avoid them in your shelter.

Stockpiling an arsenal.

It may not result in total breakdown, but storing bleach is likely to lessen the effectiveness of the product. Sodium hypochlorite solutions have been shown to decompose rapidly, so much so that the EPA requires manufacturers of bleaches with 5.25 to 12.5 percent sodium hypochlorite to add special language to their label: “Degrades with age. Use a test kit and increase dosage as necessary to obtain the required level of available chlorine.”

The staff at Pharmacal Research Laboratories use chlorine test strips to measure the strength of their solutions, says Quality Assurance Lab Manager Tammy Marotta Fleischer. The extra precaution is not, they discovered, extraneous. When they conducted a test on just how quickly bleach solutions decompose, Fleischer and her colleagues began by storing a simple solution of 18-percent sodium hypochlorite in a capped opaque bottle on a countertop in their laboratory. The idea was to simulate a real-life situation at room temperature, with lights coming on in the morning and going off at night during the workweek. In analyzing daily samples from the bottle and recording the percentage of active ingredient, the staff found that after only five days, the level of sodium hypochlorite fell to 15.68 percent; at 20 days it was 13.72 percent. By day 35, it had plummeted to 12.74 percent—only two-thirds its initial strength.

Quinlan has seen this—or, more accurately, smelled it—for himself in shelter settings. Recently on a visit to a local humane society in Arizona, he spotted a bottle of bleach on a cart, opened it, and lifted it to his nose.“I couldn’t smell any chlorine,” he says. “So I put the cap back on, I shook it up, opened it up again. Still no chlorine. Bleach dissipates very quickly, even if it’s in a sealed bottle.”

“What’s happening across the country is people are buying bleach in gallon jugs and even in some places stockpile it,” says Quinlan, “and basically what you have is a pallet full of water after it sits there for a month or two.”

Once the bleach is diluted for daily routines, of course, the degradation occurs even more quickly, he says, using the analogy of a swimming pool that’s fit to dunk into almost immediately after chlorine has been added to it. “When you mix bleach and water together to make your disinfectant,” says Quinlan, “the chlorine’s only present for anywhere from around a half an hour to an hour, depending on how much you started with.” For routine use, fresh buckets of diluted bleach should be prepared daily or each time you disinfect. As long as your surfaces are already clean, cool water is best; hot-water bleach solutions release more chlorine gas into the environment, putting more irritants in the air and leaving less disinfecting power in the bucket.

Pouring before scrubbing.

Maybe it’s all those childhood summers in the pool or those days spent at the laundromat, but somehow the human mind seems to have been wired to associate the smell of bleach with cleanliness. Cleaning and disinfecting are not one and the same, however, and sodium hypochlorite has the power to do only the latter. It may whiten and inactivate the algae on a wall, says University of Tennessee virologist Leon Potgieter, but it’s going to leave a trail of dead residue in its wake.

While bleach is rather shallow in its activity and never moves past the surface of things, the inherent cleaning abilities of some disinfectants are enhanced by detergent additives that lift and remove residue. Quaternary ammonium compounds are “cationic surfactants,” meaning that they reduce the surface tension and actually attract negatively charged surfaces, including microorganisms. Detergents penetrate the outer layers, helping the dirt and germs float up to be encapsulated and dispersed.

But bleach is less adventurous; it kills the germs it comes into contact with on the surface but doesn’t explore the cracks and crevices. Dirt, feces, and other organic matter act like conspirators in this anti-cleaning campaign, not only reducing the activity of sodium hypochlorite but also protecting the germs from coming into contact with the solution. The combination of bleach and organic materal can even release a toxic gas and produce potentially carcinogenic compounds, says Fleischer.


Precleaning, therefore, is a necessary step, though the temptation to skip it and hope for the best is understandable: whether you use a quat and then bleach or just a straight quat, the process requires two applications of solution—one to help clean and one to disinfect—and that’s only after complete removal of leftover food, crumbs, feces, litter, and any other items requiring disposal. (See “Being Chemically Balanced Is No Guarantee” for tips on basic cleaning.) Rinsing between steps is critical; mixing products can create toxic fumes or inactivate the effectiveness of both solutions.

Buying any old bottle you see.

For years, veterinarians and other animal care experts have been recommending dilution of bleach at a rate of 1 part chemical to 32 parts water. But that assumes that the product you’re using contains 5.25 percent sodium hypochlorite.

In fact, says, Fleischer, the percentage of active ingredient in household bleach can vary tremendously, even going as low as 2 percent. And if it’s not an EPA-registered product, the formulators don’t have to follow the same criteria as do manufacturers of solutions intended for disinfection; thus, a product sitting in a hot warehouse in Florida could decompose before it ever makes it to the shelves. While a few household bleach manufacturers are EPA-approved, many are not, wrote Fleischer and co-author Amy Ingraham in an article on disinfection that was published in Lab Animal: “The other companies are manufacturing a product that will clean and brighten your clothes, but may not disinfect your facility. In fact, the percentage of active ingredients in these products may be too low for effective sanitizing.”

On its new website,, the Clorox Company even makes this distinction, advising potential buyers that not all of its bleach products are created equal. Only Ultra Clorox is EPA-registered and made for industrial use: “Our fragranced and Advantage Clorox Bleaches are not sold as registered disinfectants. If you need a registered disinfectant, you can purchase EPA-registered Ultra Clorox Bleach at almost any store that sells laundry products.”

Some companies sell EPA-registered bleach that’s about twice as concentrated as Ultra Clorox. Animal Health Technology’s bleach product comes in a black drum to prevent any exposure to light, which contributes to decomposition. “We start out with 12 and a half percent, and we run it through a mixing station that dilutes it correctly for the user,” says Quinlan.

Whatever the concentration of the product you’re applying, you need to add enough water to match the level of sodium hypochlorite you’d achieve with a 1:32 dilution of bleach that lists its active ingredient at 5.25 percent. While this mixture is generally safe enough to be used around people and animals when properly applied and rinsed, it’s also strong enough to kill even feline panleukopenia and feline calicivirus, according to a study published in the American Journal of Veterinary Research (“Virucidal disinfectants and feline viruses,” F.W. Scott, Vol. 41, No. 3, 1980).

Since there is so much variation in product formulations, Hurley has devised a formula for figuring out how many ounces to use in each gallon of water no matter what brand you’re using: Simply divide the number 21 by the percentage of sodium hypochlorite. See “Following the Formula” sidebar for a complete explanation.

There’s yet another wrinkle in the bleach use recommendations. Although the 1:32 dilution of 5.25-percent solutions has been proven sufficient to kill almost everything likely to lurk in the shelter environment, it won’t kill ringworm, says Hurley. Repeated applications of 1:10 solutions are required to do the job, she says. “The only thing that kills ringworm in one application is undiluted bleach, but we don’t recommend that just because it’s too caustic and bad for staff and bad for kitties to breathe,” she says. “If you already know of a case or you’re having repeated occurrences of ringworm in your facility and you’re just not sure where the contamination is, it would be worth going through and cleaning with that higher concentration, taking appropriate precautions with masks and ventilation.”

There is no benefit to using higher-than-recommended concentrations for anything else, she says. In fact, it could be dangerous (see “Great Points in the Fine Print”).


A Change in Recommendations

  • Because the Clorox Company marketed its Ultra Clorox as 25 percent stronger and advised users to use 25 percent less, The HSUS and others have previously advised that Ultra Clorox be diluted at a 1:43 ratio. But further examination of the active ingredients and of the science behind dilution rates has revealed that Ultra Clorox is not as strong as it first appeared. At only 6 percent, this product should be diluted at about the same level—or only slightly less—as the brands with 5.25 active ingredient. Dividing 21 by 6 (see “Following the Formula” below) gives you 3.5 ounces, or slightly less than half a cup.

Measuring Up

Use the following chart to determine ounce-to-cup conversions in bleach dilutions.

If you need...Use...
4 oz./gallon of water 1/2 cup of bleach per gal.
3 oz./gallon of water 3/8 cup of bleach per gal.
2 oz./gallon of water 1/4 cup of bleach per gal.
1 oz./gallon of water 2 tablespoons of bleach per gal.

See for more conversions.

Following the Formula

    To make sure you’re using enough bleach to disinfect but not so much that you’re creating an unsafe environment, you need to create a mixture that matches the concentration you’d achieve by diluting a 5.25 percent sodium hypochlorite solution at a ratio of 1 part chemical to 32 parts water.

    No matter what product you’re using, you can match that level by following this simple formula provided by Kate Hurley, DVM, director of the Maddie’s Shelter Medicine Program at the University of California, Davis: Take the number 21 and divide it by the percentage of sodium hypochlorite in the product you’re using. This will give you the number of ounces per gallon you should use. Written out in short form, the formula would be: 21 ÷ (percentage of active ingredient) = ounces per gallon of water.

    For example, by following this formula when using a bleach product that lists the active ingredient at 5.25 percent, you would come up with an answer of 4 ounces per gallon. When using a bleach product that lists the active ingredient at 12 percent, you would come up with 1.75 ounces per gallon.

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