Wildlife that degrades your indoor air quality

We are all for wildlife–when it stays in the wild.  Some critters think they have hit the jackpot when they come into your home, however, and it takes some work to get them out and keep them out.  Here are the most common ones that can downgrade your health and air quality.

1. Mice and rats: According to a study in Baltimore, in a community with high levels of both mouse and cockroach allergens, there was strong evidence that mouse allergen is the major indoor allergen responsible for asthma among Baltimore City children. Although cockroach allergen might have some effects on asthma in this population, mouse allergen appears to be the stronger driver of worse asthma because it was strongly associated with a range of outcomes, including acute asthma visits, pulmonary inflammation, and lung function. (Mouse allergen is the major allergen of public health relevance in Baltimore City)

What exactly are people allergic to in mice?  We are more prone to notice rodent droppings than urine, but rodent urine contains proteins that become airborne as it dries, which can trigger allergic reactions and respiratory irritation. Over time, the smell intensifies, but even before that, the particles often begin circulating through the home’s air system. (Wildlife’s Effect On Indoor Air Quality)  Once the particles are in the air, they can be inhaled, or settle in the dust anywhere in a home to be disturbed and inhaled later.  Skin cells, hair and saliva from rodents also contain allergens, and potentially deadly microbes (rodent feces can contain hantavirus). An interesting study showed that the highest level of mouse allergens were generally found in the kitchen, but the type of flooring and presence of food debris are not associated with elevated risk for kitchen floor allergen levels (meaning even kitchens without food debris might have high levels of allergens).  In other (nonkitchen) rooms, however, allergen levels and food debris did correlate. For example, food debris observed in the living room is associated with elevated living room upholstery mouse allergen levels.  Finally, kitchen floor mopping, as opposed to vacuuming, carries a marginal increase in risk of exposure, meaning, it’s better to use a HEPA vacuum before you mop, in order to reduce risk of disturbing dust and allergens. (National prevalence and exposure risk for mouse allergen in US households)

Mice and rats induce fear in people more than most insects, so sometimes it’s necessary to have an exterminator come to “handle” the problem.  There are many non-toxic ways to get rid of mice and rats yourself, however.  Baits and traps can be set in places where children and pets don’t go (like under appliances or cabinets), and just by meticulously sealing up holes in walls and floors, you can prevent rodents from re-entering the home.  If an exterminator just wants to poison the mice but does not address the rodent “highway” of holes in your home’s exterior (in the crawlspace, attic and walls), then it’s best to find another professional!  This page from the National Center for Healthy Housing has additional tips for excluding rodents from your home.  Of course, if you can tolerate and keep a cat, cats are great deterrents to rodents living in and around your home!

2. Cockroaches are a close second behind mice and rats because cockroaches are common and they have a big effect on a developing child’s respiratory system and their likelihood to develop asthma.  There are two principal domestic cockroach species in the US, Blattella germanica (German cockroaches) and Periplaneta americana (American cockroaches).  The German type are small, usually less than ¾ inch long, and reproduce quickly.  (I know this from experience; one time I “recycled” someone else's moving boxes, which must have had a few in them, and within weeks they had developed a large colony in my kitchen.)  The American type are larger, up to 2 inches long, and require warmer, more humid conditions to reproduce, so they aren’t as prolific.  Both species produce several potent allergens and transfer them to the dust and air by depositing saliva, cells, feces and body parts all over our homes.  For example, they shed large quantities of endotoxins through their droppings.  Allergens can be found throughout the house: kitchen, bedroom, bathrooms, etc., and the highest levels of allergens are usually found in the kitchen, but because people lay down in beds and children play on floors frequently in the family room, bedrooms and family rooms are usually more important for sensitization.   Exposure to cockroach allergens in the first three months of life has been associated with repeated wheezing and asthma, and it’s an important public health problem.   Emergency department (ED) studies of asthma carried out in Charlottesville, Virginia; Atlanta, Georgia; and Wilmington, Delaware demonstrated that sensitization to cockroach was an important risk factor associated with asthma admissions to the ED for both adults and children. (Cockroach allergens and asthma) 

Despite the ease in which we’re sensitized to these allergens, it can be difficult (but possible!) to get rid of the allergens.  First, professional extermination is almost always necessary; from our own experience, boric acid and diatomaceous earth did not work against a well-established German cockroach infestation!  Non-toxic chemicals include Gentrol Point Source (a bait containing insect growth regulator),Keeping a clean home and sealing up food and garbage will help, but if you live in a multi-family unit like an apartment complex, condominium or townhome, the critters can live in your home and “dine out” in others’ who aren’t as clean as you!  Therefore, urge the landlord to exterminate all the units, and all the rooms in the units.  In an article reviewing a 2025 study in Raleigh, North Carolina, two groups of homes were studied, but only one group was consistently treated for cockroaches.  Homes that remained untreated consistently showed high levels of both allergens and endotoxins throughout the study. In contrast, most units that underwent extermination were cleared of cockroaches and showed substantial reductions in both allergens and endotoxins. "When you eliminate cockroaches, you eliminate their allergens. Small decreases in cockroaches don't lower allergen levels because the remaining live cockroaches deposit more allergens," Coby Schal, a co-author of the study, said. "Endotoxins significantly decreased in homes where cockroaches were eliminated. This paper shows that the cockroach is the most important depositor of endotoxin in infested homes." (Cockroaches are secretly poisoning indoor air)  You can reduce cockroach allergens and endotoxins by cleaning regularly. Vacuum carpets and upholstered furniture with a vacuum equipped with a HEPA filter. Wash bedding and curtains in hot water to eliminate allergens. Use air purifiers with HEPA filters to reduce airborne allergens. (Cockroach Allergy Guide: Symptoms, Triggers & Treatment)   If you’re diligent about treatment and cleaning, you can make a good impact on reducing cockroach allergens for your family! 

3. Bats and birds: While typically birds tend to nest in eaves and vents (the outer edge of your home), bats can squeeze through the slats of an attic vent to make your attic their home.  Birds will leave feathers and droppings; feathers rarely cause an allergic reaction, but the mites in feathers and dead skin cells can be highly allergic. (Allergy to feathers)  Droppings from birds and bats can carry Histoplasma capsulatum (causing histoplasmosis) and Cryptococcus neoformans (causing cryptococcosis).  In addition, bats are known carriers of rabies.  Since HVAC ducts and units are frequently placed in attics, it’s very important to keep birds and bats out of the space so that these microbes don’t get sucked into your home’s circulating HVAC system.   Once an exterminator rids the space of wildlife, they need to be diligent to place wire mesh (also called hardware cloth or anti-rodent mesh) over vents and seal up small holes to keep birds, bats and other wildlife out.   They will know the local regulations; in many states, bats are protected mammals. (Nuisance Wildlife 101)

4. Squirrels, raccoons and opossums are good climbers, so they can easily make your attic their home; raccoons and opossums have also been known to live near the ground, so the crawlspace or any void under your foundation is an option too!  When raccoons and opossums are near the ground, they can be a danger to children and any pets around your home, because they have the ability to kill small animals (they have been known to kill chickens), and even scratches and bites can quickly become infected.   The best way to get rid of these animals is to watch for when they exit your home, and close up the hole.  Once again, use hardware cloth metal mesh behind vents so that air can flow freely, and check out this video of how to use it to keep animals like groundhogs from burrowing under your home or shed.  Groundhogs can be especially detrimental in destabilizing foundations, and even whole buildings, because they move so much dirt around and under a pier (if they are shallow piers) that it can actually become vulnerable to collapse.  Once you’ve sealed them out, check for any damage to AC ducts, wires and structure that they may have inflicted with their sharp teeth and instinct to build nests. 

It’s surprising and sometimes frightening to have wildlife invade your home, but do not let them stay; health and safety of the human inhabitants is the primary reason that building inspectors demand quick action to evict and clean up after wildlife.  When the situation seems overwhelming, search “non-toxic exterminators” or visit BeyondPesticides.org to explore options, resources and professionals that won’t use toxic chemicals to evict the wildlife.

 Photo by Joshua J. Cotten on Unsplash