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How to Protect Yourself Against Indoor Air Pollution

Burning aromatic incense smoky stick for meditation and relaxing.
Photo: / AliceCam

Haze lingering low over a city. Bumper-to-bumper traffic pumping out noxious fumes. Particulate-laden smoke billowing from factory towers. These are typical scenes we might imagine when we think of air pollution, but there are less obvious and arguably more impactful sources of pollution occurring inside our homes, schools, and workplaces. Indoor air quality is often much lower than outdoor air because of common indoor air pollutants.

A study from the Environmental Protection Agency (EPA) has demonstrated that indoor air is 2 to 5 times more polluted than outdoor air, regardless of whether it is in a rural or highly industrialized area. Since the average person in an industrialized country like the United States spends 90% of their time indoors, the result is chronic exposure to indoor pollutants. The exposure is even more dramatic for those who spend even more time indoors, including infants, older adults, and people who are chronically ill. [1] 

In the 1970s, the World Health Organization coined the term “sick building syndrome” to explain adverse health effects that were assumed to be related to poor indoor air quality in certain buildings. The term “building-related illness” was added to describe adverse health effects directly linked to specific airborne contaminants inside buildings. [2] 

Common Indoor Air Pollutants  

Many indoor air pollutants are invisible, including but not limited to: volatile organic compounds, semi-volatile organic compounds, fragrance chemicals, carbon monoxide, carbon dioxide, radon, mold spores, and dust mites.    

Volatile Organic Compounds 

Volatile organic compounds, commonly referred to as VOCs, are released as gases from certain liquids or solids. [3] While some VOCs exist harmlessly in nature, such as flower aromas, anthropogenic sources of VOCs include toxic substances that contribute to indoor air pollution. When we refer to furniture or building materials “off-gassing,” we are referring to the release of VOCs. From an indoor air pollution perspective, the VOCs of primary concern are solvents and formaldehyde.  

Solvents are found in products such as carpet, vinyl flooring (PVC), wallpaper, paints, varnishes, nail polish, cleaning products, fragrances, and clothing that has been dry-cleaned with perchloroethylene. When paraffin wax candles are burned, they release VOCs such as benzene, toluene, and acetone. [4] To put this in perspective, benzene and toluene are also solvents used in diesel fuel.  

Formaldehyde is used in pressed-wood products such as medium-density fiberboard, particleboard, and plywood. These products are commonly found in cabinetry and furniture such as dressers, tables, and beds. Even upholstered products can have formaldehyde in the interior frames.  

Formaldehyde can also be found in other common household products such as upholstery foam, non-iron fabrics, wallpaper, glues, paints, lacquers, laminate flooring, insulation materials, fertilizers, pesticides, and preservatives used in cosmetics, dishwashing liquid, and fabric softener. [5] It can enter the home through cigarette smoke and “unvented fuel-burning appliances such as gas stoves, wood-burning stoves, and kerosene heaters.” [6] 

Exposure to VOCs such as solvents and formaldehyde has been linked to eye irritation, nose and throat discomfort, allergic skin reactions, liver damage, nausea and vomiting, kidney damage, fatigue, dizziness and loss of coordination, headaches, central nervous system damage, and cancer. [7]  

Semi-Volatile Organic Compounds  

Semi-volatile organic compounds (SVOCs) are considered a subgroup of VOCs. These are compounds that typically remain liquid or solid at lower temperatures, compared to VOCs, which are easily released into the air as gas at lower temperatures. [8] SVOCs are considered some of the most harmful indoor toxins because they can reach very high concentrations, and unlike VOCs, they are not as easily mitigated by ventilation.  

SVOCs include substances such as pesticides, PCBs, flame retardants, and plasticizers such as phthalates. These substances primarily attach to house dust and settle on surfaces in the home like furnishings, drapery, floors, and walls.  

A common source of pesticide residue in the home is cotton, which is one of the most intensively sprayed crops on the planet. Cotton is ubiquitous throughout our homes in upholstery fabrics, drapery, bedding, pillows, and clothing. Look for products and clothing made with organic cotton certified by the Global Organic Textile Standard (GOTS) to reduce your exposure to pesticides.  

PCBs were banned by the EPA in 1979 after they were linked to adverse effects on human health, but they can still be found in electronics, electrical equipment, and fluorescent lighting manufactured prior to this time. If a ballast fails in a pre-1979 fluorescent light fixture, PCBs can leach into the air in significant concentrations and contaminate exposed surfaces. Thus, it is recommended to remove any pre-1979 fluorescent lighting before this can occur. [9] 

Flame retardant chemicals are used extensively in everyday products such as upholstered furniture, mattresses, electronics, appliances, wires and cables, child car seats, carpets, and insulation. These chemicals are released into house dust and then ingested through inhalation or hand-to-mouth contact. Flame retardants have been linked to several adverse health effects such as hormonal disruption, lowered IQ in children, and cancer. A 2011 peer-reviewed study in Fire Safety Science also proved that chemical flame retardants in the home have no established fire safety benefit. [10] 

Fragrance Chemicals  

Over 3,000 ingredients can hide behind the word “fragrance” on a product label, including chemicals that have been scientifically proven to be harmful to human health. [11] Fragrance chemicals typically fall under the designation of VOCs or SVOCs listed above. Manufacturers are not required to disclose these ingredients under “trade secret” protections by the International Fragrance Association, and these ingredients are not safety tested by any governmental agency because the fragrance industry regulates itself. [12] 

Air fresheners, incense, candles, reed diffusers, laundry detergent, fabric softener, cleaning products, cosmetics, and personal care products can all be vectors for bringing fragrance chemicals indoors. Phthalates, which help scents last longer, are one of the main chemicals of concern. They were found in 86% of air fresheners tested by the Natural Resources Defense Council, including products that were marketed as “all-natural” or “unscented.” [13]  

Phthalates have been linked to cancer, hormonal disruption such as early puberty and infertility, human reproductive and developmental toxicity, birth defects, respiratory problems, genital malformations, allergies, asthma, and even premature death. [14] Children and unborn babies are especially sensitive to the effects of phthalates. [15] 

Carbon Monoxide  

Carbon monoxide is a colorless, odorless, tasteless gas that is fatal in high concentrations. It can accumulate indoors from leaking chimneys and furnaces, back-drafting furnaces, wood stoves and fireplaces, gas stoves, gas water heaters, unvented kerosene and gas space heaters, gasoline-powered generators, vehicle exhaust from attached garages, and tobacco smoke. [16]  

It is vital to have a carbon monoxide detector on each level of any home with a gas-powered appliance, a wood stove or fireplace, or an attached garage. Place the alarm near sleeping areas and make sure it is loud enough to wake you. [17] A carbon monoxide alarm is different than a smoke alarm, but there are some alarms that can detect both smoke and carbon monoxide separately—so check the label carefully.

Carbon Dioxide  

Carbon dioxide is produced when we exhale. A typical carbon dioxide level in a room with adequate ventilation is between 400 and 1,000 parts per million (ppm). Inadequate ventilation and crowded spaces can cause levels to rise to unhealthy concentrations. A level between 1,000-2,000 ppm is associated with drowsiness and complaints of poor air. A level between 2,000-5,000 ppm is associated with these same complaints in addition to poor concentration, headaches, increased heart rate, and nausea. Levels beyond 5,000 ppm are unusual and may be an indicator of other gases in the air. This is the level at which oxygen deprivation could occur. [18] 

If a building does not have an HVAC system that supplies fresh outdoor air, consider leaving the windows cracked open when climate and safety allow. Alternatively, open windows for a few minutes every hour to allow fresh air to enter the building and balance oxygen and carbon dioxide levels. In crowded rooms like classrooms and workplaces, consider using a carbon dioxide sensor to make sure carbon dioxide levels remain below 1,000 ppm.


Radon is a colorless, odorless, radioactive gas that is produced when radioactive metals break down in soil, rocks, water, and certain building materials. It can leach into homes, accumulate in high concentrations, and cause serious adverse health effects. It is the second leading cause of lung cancer, responsible for more deaths than secondhand smoke. It is typically linked to buildings in areas with high soil concentrations of radioactive metals, but the EPA recommends all buildings be tested for radon. [19] A simple test kit or radon professional can be found on


Mold is a well-documented indoor pollutant that has serious adverse impacts on human health. It mainly affects the respiratory system, though a much wider range of health problems have been reported. [20] It can proliferate in the presence of excess moisture, most commonly from water leaks or elevated humidity levels that lead to condensation. Visible mold is considered the tip of the iceberg because it signifies the presence of further invisible spores and mycotoxins which also negatively affect health. Any water leaks should be thoroughly cleaned and dried within 24-48 hours to prevent mold growth. Mold in high-humidity areas such as bathrooms can be prevented with adequate ventilation, regular cleaning, and a dehumidifier if needed.  

It is not recommended to clean mold with bleach, as it does not penetrate the underlying mycelium, and carries its own toxicity risk. White distilled vinegar is a better non-toxic choice for cleaning small areas of mold as it has demonstrated antifungal activity in studies. [21] However, note that vinegar should never be mixed with bleach or hydrogen peroxide, as this can create toxic gases.  

Any mold cleanup should be undertaken with adequate personal protective equipment as suggested by EPA guidelines. The EPA suggests that any area of mold greater than 3 feet by 3 feet requires professional remediation. [22]  

Dust Mites 

One of the most common indoor allergies is a dust mite allergy, also known as a house dust allergy. The major trigger of this allergy is dust mite droppings, rather than the mites themselves. [23] Dust mites proliferate in soft surfaces such as bedding, carpet, and upholstered furniture. Washing bedding weekly in hot water, keeping upholstered furniture to a minimum, and choosing hard floors over carpets are all recommended strategies to reduce dust mite populations indoors.  

Indoor Air Pollution May Be Getting Worse

Despite documented risks to human health, toxic substances are still found in many building materials, furnishings, and cleaning products. Fragranced products are widespread and heavily marketed to consumers as the cornerstone of a fresh, clean home.   

Building regulations in the United States changed after the 1973 oil embargo. With energy conservation in mind, the requirement for outdoor air ventilation per person dropped from 15 cubic feet per minute (cfm) to 5 cfm. [24] Any decrease in ventilation increases the concentration of pollutants in the indoor air. The standard was eventually revised in 1989, reverting to a requirement of 15 cfm per person.  

Even though the standard was revised, some well-intentioned energy conservation strategies still prioritize a tight building envelope to prevent heat loss and drafts. If mechanical ventilation is not sufficient and occupants do not open windows regularly, this is a recipe for increased indoor air pollution.    

How to Improve Indoor Air Quality  

Begin with the process of elimination. Some of the most common indoor pollutants can be easily avoided by removing air fresheners, candles, incense, and other fragranced products from indoor spaces. As an additional measure, it is not recommended to use essential oil diffusers for longer than one hour per day. [25]  

Another simple step to reduce pollutants in the home is to remove shoes at the door. This will limit the amount of bacteria, pesticides, herbicides, heavy metals, and asphalt chemicals tracked indoors. This is especially important in homes where small children are present, as they tend to spend more time playing on the floor and ingesting these substances through hand-to-mouth contact.  

Check the labels of cleaning products and personal care products for the word “fragrance,” which indicates undisclosed and potentially toxic ingredients. When shopping for alternatives, avoid products that are marketed as unscented, because sometimes fragrance is added to a product to neutralize scents from other ingredients. Look for fragrance-free products instead. Alternatively, our homes can be cleaned with natural, inexpensive, non-toxic ingredients such as baking soda, castile soap, and vinegar. Additional sanitization can be achieved with a steam cleaner.  

Before purchasing furniture or other homewares, it is always worth inquiring with the manufacturer whether they contain flame retardants, formaldehyde, PVC, or phthalates. While not an exhaustive list, these are some of the main chemicals of concern that are commonly found in homewares.  

Indoor VOC levels can be reduced with regular ventilation and air purifiers with activated carbon filters. This type of filtration is also recommended for homes in areas that are prone to traffic fumes and wildfire smoke. SVOCs can be reduced by keeping house dust to a minimum. Use a vacuum with a HEPA filter bag instead of a dust cannister, as these can release pollutants into the air when they are emptied. The brush attachment on vacuum cleaners is useful for cleaning upholstered furniture and drapery.  

Air purifiers with HEPA filtration are recommended to reduce mold spores, pollen, dust mite droppings, bacteria, and viruses circulating in the air. It is essential to replace the filters according to manufacturer’s instructions and choose an appropriately sized machine in relation to the size of the indoor space. An air purifier in each room is ideal for optimum filtration, especially if there are periods of time when the doors are closed.  

There are several air purifiers available with combination HEPA and activated carbon filters, which is the ideal combination to remove as many indoor pollutants as possible. It is recommended to avoid ion generators and other ozone generating air cleaners as these can have an adverse impact on human health. [26]  

A simple hygrometer will give an indication of relative humidity levels indoors, which should fall between 40-55% for optimum human comfort and prevention of mold growth. A hygrometer can be placed in each room, or at least in the most moisture-producing spaces such as kitchens and bathrooms. A dehumidifier can be used to reduce relative humidity levels when they exceed 55%, helping to prevent condensation that leads to mold growth.  

Mindful purchasing, adequate ventilation, testing for toxic gases, regular cleaning, and air purification are all strategies that can reduce indoor pollutants. Many of these are low-cost actions that can be implemented immediately. Indoor pollution is not inevitable. With the right methodology, “sick building syndrome” can be a thing of the past.  


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Hannah Richards

Hannah Richards holds a Master of Architecture degree and has been working in the field of interior architecture and design since 2011.

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