Indoor Air Quality

In recent years, comparative risk studies performed by EPA's Science Advisory Board have consistently ranked indoor air pollution among the top five environmental risks to public health. Indoor air quality problems can be subtle and do not always produce easily recognized impacts on health. Symptoms include headaches, fatigue, shortness of breath, sinus congestion, coughing, sneezing, dizziness, nausea, and irritation of the eye, nose, throat and skin. Due to varying sensitivities, IAQ problems may affect a group of people or just one individual and may affect each person in different ways.

Potential Sources of Indoor Air Pollution:

  • Mold
  • Tobacco Smoke
  • Carpet
  • Household Cleaning Products
  • Appliances
  • Radon
  • Pet Dander

How to Improve Indoor Air Quality

  • Source Control: Eliminate individual sources of pollution or reduce their emissions.
  • Improve Ventilation: Weather and outdoor air quality conditions permitting, bring fresh, outdoor air into your home by opening doors and windows. Use fans to circulate air. 
  • Change HVAC system filter: During wildfire smoke season, switch to MERV 13 or higher rated filter depending on what your system can handle.
  • Use portable HEPA air cleaners: Air filtration can be an effective supplement to source control and ventilation. Using a portable air cleaner and/or upgrading the air filter in your furnace or central heating, ventilation, and air-conditioning (HVAC) system can help to improve indoor air quality.

What is Asthma?

Asthma is a lung disease that inflames and narrows the airways. Asthma causes recurring periods of wheezing, chest tightness, shortness of breath, and coughing. Indoor and outdoor air pollutants, stress, changes in temperature, colds and other infections, and exercise can trigger asthma attacks.

Asthma is a chronic disease, like diabetes and high blood pressure. Even when you are feeling just fine, the asthma is still there and can flare up at any time. For individuals with moderate to severe asthma, their condition may require daily attention to maintain control.

Keeping Your Asthma Under Control

  • Take your medicines as prescribed.
  • Avoid your asthma triggers.
  • Monitor your asthma.

By working closely with your doctor or other health care provider, you should be able to learn how to control your asthma. Once it's controlled, you should be able to live a normal active life. When asthma is under control, you should have few, if any, asthma symptoms.

 Montana Asthma Control Program

The Montana Asthma Control Program maintains resources for Montanans and works with a variety of partners to reduce the burden of asthma statewide. The MACP is committed to improving the quality of life for all Montanans with asthma. Please visit for more information about MACP activities and general asthma resources. 

What are molds?

Molds are tiny microscopic organisms that digest organic matter and reproduce by releasing spores. Molds are a type of fungi and there are over 100,000 species. In nature, mold helps decompose or break-down leaves, wood and other plant debris. Molds become a problem when they go where they are not wanted and digest materials such as our homes.

What makes molds grow in my home?

Mold enters your home as tiny spores. The spores need moisture to begin growing, digesting and destroying. Molds can grow on almost any surface, such as wood, ceiling tiles, wallpaper, paints, carpet, sheet rock, and insulation. The mold grows best when there is lots of moisture from a leaky roof, high humidity, or flood. There is no way to get rid of all molds and mold spores from your home. But you can control mold growth by keeping your home dry.

Can I be exposed to mold?

When molds are disturbed, they release spores into the air. You can be exposed by breathing air containing these mold spores. You can also be exposed through touching moldy items, eating moldy food or accidental hand to mouth contact.

Do molds affect my health?

Most molds do not harm healthy people, but people who have allergies or asthma may be more sensitive to molds. Sensitive people may experience skin rash, running nose, eye irritation, cough, nasal congestion, aggravation of asthma or difficulty breathing. People with an immune suppression or underlying lung disease, may be at increased risk for infections from molds.

A small number of molds produce toxins called mycotoxins. When people are exposed to high levels of mold mycotoxins they may suffer toxic effects, including fatigue, nausea, headaches, and irritation to the lungs and eyes. If you or your family members have health problems that you suspect are caused by exposure to mold, you should consult with your physician.

When is mold a problem?

You know you have mold when you smell the "musty" odor or see small black or white specks along your damp bathroom or basement walls. Some mold is hidden growing behind wall coverings or ceiling tiles. Even dry, dead mold can cause health problems, so always take precautions when you suspect mold.

Mold is often found in areas where water has damaged building materials and furniture from flooding or plumbing leaks. Mold can also be found growing along walls where warm moist air condenses on cooler wall surfaces, such as inside cold exterior walls, behind dressers, headboards, and in closets where articles are stored against walls. Mold often grows in rooms with both high water usage and humidity, such as kitchens, bathrooms, laundry rooms, and basements. If you notice mold or know of water damaged areas in your home, it is time to take action to control its growth.

When should I sample for mold?

You don't need to sample for mold because in most cases you can see or smell mold. Even a clean, dry house will have some mold spores, but not enough to cause health problems. If you smell mold it may be hidden behind wallpaper, in the walls or ceiling, or under the carpet. If you suspect you have hidden mold be very careful when you investigate, protect yourself from exposure in the same manner as you would for a clean-up.

Can I control mold growth in my home?

Yes you can. Dry out the house and fix any moisture problems in your home:

  • Stop water leaks, repair leaky roofs and plumbing. Keep water away from concrete slabs and basement walls.
  • Open windows and doors to increase air flow in your home, especially along the inside of exterior walls. Use a fan if there are no windows available.
  • Make sure that warm air flows into all areas of the home. Move large objects a few inches away from the inside of exterior walls to increase air circulation.
  • Install and use exhaust fans in bathrooms, kitchens, and laundry rooms.
  • Ventilate and insulate attic and crawl spaces. Use heavy plastic to cover earth floors in crawl spaces.
  • Clean and dry water damaged carpets, clothing, bedding, and upholstered furniture within 24 to 48 hours, or consider removing and replacing damaged furnishings.
  • Vacuum and clean your home regularly to remove mold spores.
  • Check around your windows for signs of condensation and water droplets. Wipe them up right away so mold can't start to grow.

What cleans moldy furniture and other items?

Should I paint over mold?

No. Don't paint or caulk over mold. The mold will grow under the paint and the paint will peel.

Cleaning Mold

1. Size the Moldy Area

Decide if you have a large or small area of mold. A small area is less than about ten square feet, or a patch three feet by three feet square. To clean a small area, follow the advice below. You may use a cotton face mask for protection.

If you have a lot of mold damage (more than ten square feet) consider hiring a cleaning professional. If the moldy area has been contaminated by sewage or is in hidden places, hire a professional. If you decide to clean up on your own, follow the guidance below.

2. Use Protection

Wear goggles, gloves, and breathing protection while working in the area. For large consolidated areas of mold growth, you should wear an Occupational Safety and Health Administration (OSHA) approved particle mask.

3. Seal the Area & Remove Items

Seal off area from the rest of your home. Cover heat registers or ventilation ducts/grills. Open a window before you start to clean up. Remove all your furnishings to a mold-free area. Clean the surrounding moldy area then follow cleaning directions below for the items you removed and the new space.

5. Bag Moldy Trash

Bag all moldy materials and tie off the top of the bag. Bring them outdoors and place in your garbage container right away.

6. Scrub Surfaces

7. Clean and Wash

Give the entire area a good cleaning, vacuum floors, and wash any exposed bedding or clothing.

What are Portable Air Cleaners?

True High Efficiency Particulate Air (HEPA) filtration units are designed to capture at least
99.97 percent of fine airborne particles larger than at least 0.3 micrometer (0.00001 inch) as specified by the United States Department of Energy. Ultra-fine particles are things like dust, pollen, mold, asbestos, and hazardous pollutants in wildfire smoke. 

HEPA filtration units are generally equipped with replaceable pre‐filters that also remove larger particulate matter, such as pollen and dust. Filtration units range in size from small portable units up to central heating and cooling systems for entire buildings. Effectiveness depends largely upon how much filtered air they deliver over a given period into a specified space. If you or someone in your family suffers from asthma or severe allergies, using a HEPA air purifier can significantly improve your quality of life inside your home.

How Mechanical Portable Air Cleaners Work

Image of Pre-filter, HEPA Fileter, Carbon Filter

Choosing a Portable Air Cleaner 

Before going to the store, do some research. Start with a list of models that are top-rated or available near you, then consider the basic criteria below. 

1. Look for a simple mechanical device with no other technologies

  • Check that a device is “mechanical” on the List of CARB-Certified Air Cleaning Devices (rather than “electronic”).

  • Avoid ion or ozone generating devices. Ozone is an irritant that can irritate your eyes, lungs, and skin. It is especially dangerous for people with respiratory conditions.

2. Find a portable air cleaner that’s large and efficient enough to clean your room. 

  • Look for a device that lists a Clean Air Delivery Rate (CADR) equal to at least 2/3 the area of the room where you’ll use the portable air cleaner (width × length, in feet). If you’re in an area that often has heavy wildfire smoke, consider a higher CADR closer to the area of the room.

  • If a room is bigger, has an open floor plan, or doors are kept open between rooms, consider getting two units. If your ceiling is taller than 8 feet, look for a slightly higher CADR. The CADR is measured at the highest fan speed, so consider finding a device with a CADR for a larger size room, or using multiple devices, and running at a lower fan speed.

  • Devices with a higher CADR are more effective but tend to be more expensive. However, even lower CADR devices will remove some level of air contaminants. Picking a lower CADR device is preferable to not having any portable air cleaner during a poor air quality event. Consider using your lower CADR device in a smaller room. 

3. Consider noise level. 

  • Pick a device that’s not so loud that it could be harmful or a nuisance and might get turned off.  

  • To reduce noise, consider finding a device with a CADR for a larger size room, or using multiple devices, and running at a lower fan speed. Turn down the fan speed for a while if it’s too loud. Remember, for an air filter to be functioning at full capacity it must be running on its highest setting.

4. Other Considerations

  • TRUE HEPA: Make sure the unit you choose labeled HEPA, not "HEPA-like". True HEPA PACs are able to filter out 99.7% of particles down to 0.3 um. Some units only filter down to 3 microns - which means they do NOT filter out smoke.

  • Upkeep: HEPA filters need to be replaced regularly, so check the cost for a replacement. A separate, washable pre-filter can improve the lifetime of the HEPA filter. 

  • Energy: Check the EnergyStar database, U.S. Department of Energy for more efficient devices, especially for a large facility with many devices. 

  • Tampering: Some units provide a “childlock” feature that restricts button use. 

  • Footprint: Some portable air cleaners are large. Before purchasing a device, consider the space it will take up.

  • Air sensor: A unit with an air sensor can adjust the fan speed automatically. 

  • Display: A display that can be turned off is helpful to use the unit at night. 

  • Do-It-Yourself: Making your own box fan filter can be a less expensive option to filter air and improve indoor air quality in a single room or designated space. See information on how to build a Do-It-Yourself Fan/Filter Room Air Cleaner at

What else can I do to improve indoor air? 

A portable air cleaner won’t remove all indoor pollutants. It’s important to remove sources of contaminants and ventilate.

  • Avoid adding to indoor air pollution. Avoid smoking or vaping, using fragrance products, or burning candles or incense. Also consider frying and broiling less often. 

  • Clean regularly with damp microfiber cloths and a HEPA-filtering vacuum cleaner. 

  • Use built-in ventilation like kitchen and bathroom exhaust fans and whole-building ventilation. 

  • Open windows and doors daily to introduce new air and clear out stagnant indoor air.. Close them if outdoor fine particulate matter (PM2.5) levels are high. You can check current and forecasted air quality at or

    • Portable air cleaners aren’t as effective when windows and doors are open, so turn them off while you’re naturally ventilating.

  • Update your HVAC system filters to MERV 13 to remove small particles. Check your HVAC specifications first to determine if your system can handle a MERV 13 filter.

More Information

HEPA Air Cleaner Selection Guide, MT DPHHS

HEPA Portable Air Cleaners for Wildfire Smoke, Climate Smart Montana

Guide to Air Cleaners in the Home, EPA

Verification Program for Portable Electric Room Air Cleaners (Clean Air Delivery Rates), Association of Home Appliance Manufacturers (AHAM)

Environmental tobacco smoke, otherwise known as secondhand smoke, is a mixture of the smoke given off by the burning end of a cigarette, or cigar, and the smoke exhaled by a smoker. environmental tobacco smoke contains more than 4,000 substances, several of which are known to cause cancer. There is no safe level of exposure to environmental tobacco smoke. In fact, people who do not smoke but who are exposed to environmental tobacco smoke, even for a short time, can suffer harmful health effects. 

The health problems associated with environmental tobacco smoke include:

  • Coronary heart disease, stroke, and lung cancer
  • Adverse reproductive health effects in women
  • In children, environmental tobacco smoke can cause respiratory infections, ear infections, and asthma attacks. It has also been linked to sudden infant death syndrome.
  • Environmental tobacco smoke exposure can produce harmful inflammatory and respiratory effects within 60 minutes of exposure which can last for at least three hours after exposure
U.S. Dept of Health and Human Services. The Health Consequences of Smoking—50 Years of Progress: A Report of the Surgeon General. U.S. Dept of Health and Human Services; 2014.
Flouris AD, Koutedakis Y. Immediate and short-term consequences of secondhand smoke exposure on the respiratory system. Curr Opin Pulm Med. 2011;17(2):110–115.


Protect yourself and your loved ones from environmental tobacco smoke by:

  • Not allowing anyone smoke in your home. Smoke from one cigarette can stay in the room for hours. Even if you smoke in a designated room, it will travel through doorways, cracks in the walls, electrical lines, ventilation systems and plumbing.
  • Not allowing anyone to smoke in your car, even with the windows down.
  • Seeking out restaurants, hotels, and bars and other places that are smokefree
  • Moving away from others who are smoking
  • teaching your children to avoid secondhand smoke.


Emerging research suggests that electronic cigarettes (also called e-cigarettes, vapes, and pod moods) contain secondhand aerosols. These aerosols contain harmful substances, including nicotine, heavy metals like lead, and cancer-causing agents and should be treated with the same precautions as environmental tobacco smoke.




 Good Indoor Air Quality is an important component of a healthy indoor environment, and can help schools reach their primary goal of educating children. Failure to prevent or respond promptly to IAQ problems can increase long- and short-term health effects of students and staff, such as coughing, fatigue, eye irritation, headaches, and allergic reactions, aggravating asthma and other respiratory illnesses. These effects contribute to higher rates of absenteeism, lowered test scores, and increased susceptibility to other illnesses. 

School personnel can take steps to remediate poor indoor air quality by

  • Using unscented, environmentally safe cleaning products in school
  • Removing trash daily to minimize odors
  • Avoid air fresheners
  • Classrooms should be free of chemicals, pests, and animals
  • Using maintained HEPA air purifiers in the classroom. Change filters regularly
  • Use traps instead of pesticides


Additional Resources:

Healthy and Safe Schools - Pollution Prevention Program | Montana State University

Wildfires and Indoor Air Quality in Schools and Commercial Buildings | US EPA