Coronavirus & indoor air pollutants: quarantine safely! Part 2

Burning incense may release pleasant scents, but they also release toxic pollutants, including fine particulate matterc
There are many sources of air pollutants indoors, but we have control over many of them!

I am a strong advocate of environmental medicine, focusing on the impact our environment has on our health. This is part 2 of a guide on indoor air pollutants. Remember that indoor air pollutants may be 100x to 1000x worse than outdoors! You should start with part 1 where I described where to look in your house for the sources of common indoor air pollutants.

Sheltering in place to stay safe against coronavirus provides a valuable opportunity to ensure our home environment is safe and healthy for ourselves and our children. The burden of pollution is higher in children because of their smaller sizes and the susceptibility of their developing organs.

To protect our households, I advocate a systematic approach to reviewing our home air quality. We should recognize that we can easily become overwhelmed by the numerous potential indoor air pollutants in our homes. To prevent that from happening, follow this pragmatic approach.

Remember, this can be a potentially valuable family activity. Exposing children to the importance of their environment at an early age is valuable for their health education, too!

Let’s dive in!

Risk of individual indoor air pollutants

Most pollutants follow a “dose dependent” relationship to disease. I summarize this risk to our health as a “toxic load”:

Equation summarizing dose-dependence on human health: Risk to our health = toxic load = potency of toxin x exposure time. This is key in appreciating indoor air pollutants.

In words? That means a less potent toxin with a short exposure time (seconds to minutes, for example) poses a relatively low risk to our health. In contrast, a potent toxin with a long exposure time (days to weeks, for example) poses a relatively high risk to our health.

We quickly find that most indoor air pollutants have poorly characterized toxic potency. Why? It is unethical to perform a study where individuals are purposefully exposed to suspected toxins. Most of our data comes from observations across time. Some data comes from tragic accidents where populations were accidentally exposed to toxins. This has been studied in large scale water contamination, industrial leaks, and occupational accidents.

Map of Flint, MI. Tragic widespread water contamination provided knowledge to us that would otherwise be unethical to study directly. Indoor air pollutants have been studied from studies like this.
Flint, MI: much of our environmental toxin knowledge comes from these tragedies

Even if potency is varying depending on the pollutant, we can characterize the exposure. It is important to recognize that exposure time can be high for home air toxins. Why?

  1. We often spend significant time at home (eating, sleeping, etc.). We are spending more time now than ever under shelter in place!
  2. We are breathing air 100% of the time at home. This represents roughly 3,000 gallons of air a day!

Therefore, the “toxic load” of many pollutants becomes high by virtue of them being omnipresent in our homes.

Systematic assessment of our indoor air pollutants

We will use the list from part one to categorize the risk of individual indoor air pollutants in our homes:

Combustible items (incense, candles, wood burning stoves, cigarettes, etc.)

  • The threat? Fine and ultrafine particulate matter, based on the combustion source. Carbon monoxide, naphthalene, volatile organic compounds (VOCs).
  • Potency? Particulate matter can have hazards greater than secondhand smoke. Naphthalene is a probable carcinogen. VOCs are a broad group of chemicals (including formaldehyde and benzene) that can have mild to severe concerns, including carcinogenesis. Carbon monoxide can be lethal if unchecked.
  • Exposure time? You can control based on the time spent burning.

Larger ignitable objects (gas or kerosene stoves, space heaters, leaks from furnaces or from the garage letting in car exhaust)

  • The threat? Carbon monoxide.
  • Potency? Can be lethal if undetected.
  • Exposure time? Based on time spent burning. Can monitor with carbon monoxide alarms.

Wood products

  • The threat? Formaldehyde. It is a resin commonly used in pressed woods and particleboard (also known as chipboard). It can leak into the air through cracks, chips, or peeling. Consider your furniture and cabinets.
  • Potency? Formaldehyde is a known carcinogen by some agencies.
  • Exposure time? Potentially long if it is in the ambient air in your kitchen (think cabinets). Formaldehyde detectors can help you determine your exposure.


  • The threat? Formaldehyde. You need to check the type of flooring you have. Hopefully it isn’t applicable to your home.
  • Potency? Formaldehyde is a known carcinogen by some agencies.
  • Exposure time? Potentially long if it is in the ambient air of your house. Formaldehyde detectors can help you determine your exposure.
A carpet being unfolded. Carpets can offgass for several days. They can release formaldehyde, among other compounds. This can represent a harmful source of indoor air pollutants.
Carpets, even if listed as “natural wool”, can still contain numerous compounds that may offgass.


  • The threat? VOC’s, formaldehyde, flame retardants.
  • Potency? VOCs and formaldehyde, as described above. Flame retardants are a problematic group of compounds that have been implicated in thyroid dysfunction, metabolism disruption, and breast, blood, testicular, and prostate cancers. Unfortunately, we have learned a lot from fire fighters who come in close contact with flame retardants frequently.
  • Exposure? Most new carpets release the majority of their VOCs within days of use. This is called “off-gassing”. A problematic scenario is a baby crawling on a new carpet. Formaldehyde can be measured to determine if your carpeting is still off-gassing that particular VOC. Flame retardant exposure can be determined by checking for a label on your carpets. It is difficult to directly measure these chemicals.

Furniture and foam products

  • The threat? Flame retardants.
  • Potency? See the section on carpets. Flame retardants are not benign substances. We have (unfortunate) data from fire fighters who have high exposure to these chemicals.
  • Exposure? Check your furniture tags listing the inclusion of flame retardants.

Electronics and kitchen appliances

  • The threat? Flame retardants (we don’t want the electrical components to start a fire).
  • Potency? See above sections on flame retardants.
  • Exposure? Depends on the specific appliance (does it contain retardants?) and where it sits in the house. Flame retardant chemical often end up in dust, so exposure may be low if the surroundings are cleaned and mopped regularly.
A printer that might emit ozone, nanoparticles, and other solvents into the air around us. These indoor air pollutants comprise an active area of research.
Printers emit many compound into the air around them, including ozone and nanoparticles.


  • The threat? Ozone, solvents, toner dust, nanoparticles.
  • Potency? Largely unknown but actively researched. Nanoparticles in particular are actively being studied. Ozone is a known respiratory irritant that can increase susceptibility to infection.
  • Exposure? Depends on your printer and frequency of use. You can check your manufacturer for emissions levels. May reduce exposure with proper ventilation of the occupied room.


  • The threat? Lead, VOCs.
  • Potency: lead is a potent toxin with far-reaching effects across the body. VOC potency is discussed above.
  • Exposure: Lead can escape from paint into dust. “Paint chips” can be consumed by children accidentally, leading to toxicity. VOC exposure depends on the type of paint used and time from application (similar to “off-gassing” as carpets, above).


  • The threat? Naphthalene (in mothballs). Pesticides (less likely if organic). Formaldehyde.
  • Potency: Naphthalene and formaldehyde are carcinogens. Pesticides can cause wide-spread problems in the body, though transmission from clothes is not well studied yet.
  • Exposure: When you wear your clothes. New clothes are most likely to have formaldehyde on them. If you have washed your new clothes you can reduce your exposure. If you wear organic cotton clothing your exposure is likely low. If you use mothballs, strongly consider an agent without naphthalene.


  • The threat? Pesticides.
  • Potency?  Pesticides can cause wide-spread problems in the body, though transmission from bedding is not well studied yet.
  • Exposure: time spent in bed (direct contact with bedding likely greater exposure than from air).


  • The threat? many toxins. Describing all of them is beyond the scope of this post. Threats are similar to candles and other combustibles.
  • Potency: severe.
  • Exposure: first or secondhand.

Stored volatile solutions or volatile gases: solvents, paints, paint thinners, etc

  • The threat? these represent many different compounds, depending on the particular solution. VOC’s are a particular concern.
  • Potency: varies depending on the particular VOC. Some VOCs (formaldehyde and benzene) are carcinogenic.
  • Exposure: may be significant depending on where the solvents are stored in your home.

Hobby items: correction fluids, adhesives, permanent markers, arts/crafts materials, sprays, aerosols

  • The threat? Many compounds, depending on the particular item. VOCs and aerosols are specific concerns.
  • Potency: some aerosols can be toxic, depending on the particle type, size, and concentration. You can read more here from the CDC.. There are several aerosol propellants used and this remains an area of active research.
  • Exposure: may be significant depending on where the items are stored in your home and whether there is adequate ventilation when in use.

Insect repellents: DEET, pet protection (flea or tick collars), etc.

  • The threat? Pesticides and other specific compounds (DEET).
  • Potency: Widespread bodily effects. See clothing and bedding above.
  • Exposure: Bringing these repellents into the home increases your exposure, particularly if in poor ventilation.

Personal care products (anything with odors or parfume)

  • The threat? many possible compounds. Phthalates may be released into the air and then inhaled by us.
  • Potency: “endocrine disruptors” potentially affecting hormonal systems in the body. May lead to obesity, cancer, reproductive disorders, etc.
  • Exposure: perfume, nail polish, liquid soap, hairspray.

Exposed insulation in walls

  • The threat? asbestos.
  • Potency: severe (mesothelioma).
  • Exposure: unfortunately, asbestos exposure does not follow a “dose-dependence”. A single exposure may lead to mesothelioma.

Fragrances (air fresheners, etc.)

  • The threat? Phthalates and VOCs.
  • Potency: Phthalates are termed “endocrine disruptors” because they alter hormone action in our bodies. This can lead to obesity, reproductive disorders, cancer, and other disorders. VOCs comprise many compounds, some of which can cause cancer (see above).
  • Exposure: air fresheners in the home may output a constant amount of phthalates and other compounds into the air. We may breathe high loads of these fragrances on a regular basis at home. This could be a high exposure.

Conclusion – indoor air pollutants part 2

Part 2 of this guide is the most extensive of the 4 part series. We can only improve the indoor air quality of our homes by systematically assessing each possible pollutant. To review, we need to consider each exposure as a “toxic load”, meaning:

Equation summarizing dose-dependence on human health: Risk to our health = toxic load = potency of toxin x exposure time. This is key in appreciating indoor air pollutants.

Once we have determined the toxic load of each component, then we can pragmatically address each pollution source. We ultimately want to decrease indoor air pollution without becoming overwhelmed or stoking anxiety. You’ll find that we can address many of these pollutants relatively easily by decreasing the toxic load from them or replacing them outright.

In the next part (#3) we’ll set up a method for determining which of these products may present enough toxic load to consider replacing.

Continue sheltering in place to stay safe against coronavirus. Keep your home as healthy as possible while doing so!

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The information provided in this post in intended for general education. It is not medical advice. While I make every effort to provide the most up-to-date information, please note that new data is continuously becoming available and may change the conclusions I present here.

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