Odor Control Strategies for the Small Animal Caretaker

Theresa Lee
From the RMCA web site, June 2004

Boy mice are notoriously stinky. One boy mouse can easily generate the stink of at least 5 girl mice or 5 rats of either gender. Relatively speaking, girl mice and either gender of rats don't smell at all! Boy mice are often discriminated against because of their odiferous nature, but they are otherwise just as deserving as any other mouse or rat. In this article I review various odor control strategies that may be used when caring for boy mice and other small animals.

"Odors" are those substances which are both able to reach our nose and able to elicit an olfactory response. "Odor control," then, is controlling those substances that reach our nose and/or controlling our olfactory response. Experts agree that the most important odor control strategies, in order of overall effectiveness, are source control, ventilation, and air cleaning. Another common odor control strategy, air additives, is also discussed. The occasional use of air additives is thought to be safe, but their continual use may affect health adversely. Notable exceptions include formaldehyde and ozone. Both are very potent toxins, and neither should ever be intentionally added to the air as an odor control strategy. All air additives should be used with caution.

Source control

  • Clean often. Replace soiled bedding with fresh bedding and clean cage surfaces and cage accessories as often as possible. Because scent marking is an important part of mouse communication, the frequency of litter changes and cage cleaning in cages of groups of mice should be tempered with the need to maintain social harmony.

  • Choice of bedding. Beddings can inhibit the processes that are capable of generating odor, but little comparative work has been done to investigate which beddings are superior in controlling overall mouse odor. Hundreds of compounds contribute to mouse odor, but ammonia is certainly among the most offensive. Of even greater concern, high levels of ammonia in bedding can also cause and exacerbate respiratory disease. One study has shown that, among 8 mouse-soiled beddings tested on an equal volume basis, the lowest levels of ammonia are found on corncob. Whichever bedding is used, bedding should always be changed before the smell of ammonia can be detected.

  • Temperature and humidity. In general, fewer odors are released in lower humidity and lower temperature conditions. However, mice cannot survive prolonged period outside a 65-80F temperature range, and, to prevent ringtail, a relative humidity range of 30-70% is recommended. Of course, health takes priority over odor, and everything possible should be done to ensure your mice remain within these temperature and humidity limits.

  • Feed additives or supplements. Pet stores now sell food products, additives, or supplements that claim to reduce odors from the inside out. Most of these products contain amino acids (e.g., Bi-Odor) or yucca schidigera (e.g., Odor Free, Deodorase) as the active odor-reducing ingredient. Very preliminary studies have shown that the use of amino acids and yucca schidigera as feed additives may help control livestock odor. More studies are needed to show this is conclusively the case in livestock, and it remains unknown if these strategies are at all effective in companion animals. Amino acids and yucca schidigera are thought to be generally safe supplements; follow manufacturer's recommendations.

  • Bathing or use of pet wipes. Because the majority of mouse odor is released from mouse urine rather than from salivary, sweat, or scent glands, bathing or the use of pet wipes will do little to control mouse odor.

  • Spay or neuter. Both spaying and neutering will alter the composition of the urine and decrease urine marking and, thus, are effective in reducing mouse odor. Both, however, are surgical procedures that can carry significant risk for mice, and I would never consider spaying or neutering mice solely for odor control purposes.


  • Opening windows. The simplest and one of the most effective strategies: "Dilution is the solution." This assumes that outdoor air is cleaner than indoor air. Depending on the time of year and your location, this may or may not be true. In addition, this method of odor control is not an option during heating and cooling seasons.

Air cleaning

  • Whole house air cleaning. If you have forced air heating/cooling, talk to a heating contractor about upgrading to the most efficient type of furnace filter (for example, HEPA furnace filters are available, but may not be compatible with your present heating system) or installing a whole house electronic air cleaner.

  • Active room air cleaning. Air purifiers use a fan motor to push room air through a series of filters. If odor control is the primary goal, choose an air purifier that includes both a HEPA filter (to remove odors attached to particulates) and an activated carbon/zeolite filter (to remove odors traveling free as molecules). Personal or desktop air purifiers are thought to be ineffective. To maximize effectiveness, choose an air purifier rated to clean the size of the entire room you wish to use it in, and change filters according to the manufacturer's recommendation.

  • Passive room air cleaning. Baking soda in a dish or satchel chemically reacts with odors in the air and thus acts as a chemical air cleaner. Activated carbon or zeolite in a dish or satchel physically traps odor molecules in the air and thus acts as a physical air cleaner. Each of these three products removes different types of odors, so it may be most effective to use all three types simultaneously. Both activated carbon and zeolite can be partially recharged by heating for a few hours to ~800C and ~400C, respectively, but these are temperatures not normally achievable in the home. Many zeolite products claim they can also be recharged by heating for a day in the sun; this may or may not be true. Replace zeolite if it no longer seems to be controlling odor. Finally, all three types of products are safe to ingest and may also be used directly in the cage. For me, however, baking soda is too dusty and activated carbon and zeolite are too expensive to use directly in the cage.

Air additives

  • Perfumes. Natural and synthetic perfumes are added to the air to mask unpleasant odors and evoke an overall pleasant olfactory response. d-limonene and methyl salicylate, for example, are natural and synthetic, respectively, perfumes used in the popular product Nilodor. These products work by adding odor to the air, not by preventing or removing existing odors. Perfumes can be added to the air occasionally with sprays or aerosols or continually with plug-ins, volatile solids, or the like. At high, chronic, oral doses, d-limonene is a known carcinogen in male rats, but it is not known if there are any associated health risks at low, chronic, inhaled doses. The occasional use of perfumes is thought to be safe, but their continual use may affect health adversely.

  • Antimicrobials or enzymes. Antimicrobials are added to the air to destroy odor-causing bacteria (e.g., Oust), or enzymes are added to the air to speed up odor decomposition (e.g., Pure Ayre). To work, these products need to come into actual contact with either the odor-causing bacteria or odors. Mixing antimicrobials or enzymes directly into livestock manure, for example, is actually a form of source control and an effective way to control manure odor. Spraying antimicrobials or enzymes into the air to control odor, however, is likely to be ineffective as (1) only a negligible percentage of odor-causing bacteria is actually aerosolized and (2) in the air, these products will almost never actually come into contact with aerosolized bacteria or odors. In theory, these products would work by preventing or removing existing odors. In reality, these products all contain perfumes, and these products, in actuality, work by adding odor to the air.

  • Nerve deadening agents. Chemicals such as formaldehyde and piperonyl butoxide are added to the air to deaden the nerves in our noses. These chemicals are included in small amounts in some air freshening products. Rather than by removing odors, these products work simply by removing our olfactory response. Formaldehyde is a very potent toxin and should never be intentionally added to the air as an odor control strategy.

  • Candles and incense. Pleasant-smelling aldehydes, alcohols, and esters are released into the air when candles and incense are burned. These products work by adding odor to the air, not by preventing or removing existing odors. Various by-products including hydrocarbons and soot particulates are also released into the air when candles and incense burn. The occasional use of candles and incense is thought to be safe, but their continual use may affect health adversely.

    Slash, a very stinky mouse

  • Ozone. Ozone generators generate and spray ozone into the air. Ozone will react almost immediately with many substances, and ozone generator manufacturers claim that by spraying ozone into the air, ozone will react and destroy odors in the air. Ozone generators, like antimicrobials and enzymes sprayed into the air, are ineffective at controlling odors because the ozone will almost never actually come into contact with odors in the air. It will, however, likely make it into your lungs and the lungs of your loved ones where it can act as a powerful respiratory disease agent. Both the Environmental Protection Agency and the American Lung Association strongly discourage the use of ozone generators. Ozone is a very potent toxin and should never be intentionally added to the air as an odor control strategy.

We currently care for 68 rats and mice, 30 of them boy mice. Pictured to the right is, by far, our stinkiest boy mouse, Slash (aka, The Slashinator, Slashie-poo, Stinky-poo). Litter is changed and cages are scrubbed once a week. We have a Honeywell whole house electronic air cleaner installed on our forced air furnace. We use a Holmes room air purifier in the mousie room, but not in the rattie room. Both the whole house and room air cleaners are only run when the windows cannot be open. The air quality where we live is good, and when the weather is nice, we open the windows and do not run the air cleaners. We keep trays of baking soda under each of the mousie cages. Our houseguests can still smell our small friends, though they tell us the smell is no stronger than having a few dogs in the house.

Boy mice are often discriminated against because of their odiferous nature, but they are otherwise just as deserving as any other mouse or rat. I hope more people out there decide to bless their lives with a boy mousie or two!

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