The health effects of wildfires
As the Los Angeles wildfires continue to rage, Mary Margaret Johnson, principal research scientist in the Department of Environmental Health at Harvard T.H. Chan School of Public Health, discusses the dangers of wildfire smoke to health, which populations are most at risk, and tips to protect yourself.
Q: What are the primary dangers of wildfire smoke to people’s health?
A: We’re finding out that there’s more and more danger than we realized. The amount of danger depends on the type of smoke—how long you’re exposed, the intensity, and your own health conditions. We found that people who have pre-existing respiratory and cardiac disorders are more at risk. For example, if you have asthma, you’re more likely to have an asthma or COPD exacerbation. If you have cardiac disease, the incidence of heart attacks and arrhythmias goes up and, neurologically, stroke increases with smoke exposure in the older population.
When a population is exposed to wildfire smoke, even with like a 10 microgram per cubic meter increase in PM2.5 [fine particulate matter] levels, we will see increases in emergency room visits and hospitalizations for respiratory and cardiac disorders.
In addition, there are other populations that we may not have thought much about previously, such as pregnant women. Exposure puts both the pregnant mom and the baby’s outcomes at risk, depending on the trimester and the level of exposure.
There are also more long-lasting impacts from smoke exposure. For example, a study done in Canada showed that when a population was exposed to wildfire smoke in the summer/fall period, the rates of influenza were higher in that community in the fall/winter period. Other studies have correlated COVID rates of infectivity and mortality with levels of air pollution and even exposure to wildfire smoke.
In our own research we’ve been studying firefighters and it’s known that they have increased rates of certain type of cancers. We’re interested in what is happening to their immune system as they’re chronically exposed to the smoke and trying to tease out where that tipping point is, if there’s a defined point at which continued smoke exposure will set them at increased risk for developing certain types of cancers.
Q: Are there any particular chemicals/metals in wildfire smoke that make it particularly dangerous? And is there anything known about the chemicals in the California wildfire smoke?
A: We do know that there are many chemicals in the smoke. It depends on what is being burned as to what the composition of the smoke is.
There are some similarities no matter where the fire is coming from, but we also know that there’s a difference between a wildland fire and a structure fire, for example, when buildings are burned. With a structure fire there’s a lot of [different] types of chemicals and plastics that are being combusted and other things that will increase the toxicity of the smoke. And we also know that there’s a difference in the type and level of toxic metals when you’re exposed to a wildland fire versus a structural fire.
In a structural fire, you have certain things like steel beams and electronics and plastics and plumbing that contain toxic metals. We know that exposure to toxic metals is not good. They can be retained in the body long term, and toxic metal exposure is associated with chronic health outcomes and cancer. And it’s not just toxic metals, you know. There are all kinds of other chemicals, for example, dioxins, polyaromatic hydrocarbons, carcinogenic compounds that are being combusted in a structure fire.
You still get some [exposure to toxic metals in a wildfire]. There are metals in the soil. So, for example, in California there are regions where the amount of chromium 6 is elevated. If that soil is combusted then that smoke will contain it. However, the levels and variety of chemicals and toxic metals are much higher with structure fires and chromium 6 exposure, for example, can increase the risk for lung cancer and cause respiratory and skin irritation.
Q: Which groups are most vulnerable to smoke exposure during wildfires?
A: I would definitely say the very young and the very old, the very young more from a respiratory perspective, because they have smaller airways and have an underdeveloped respiratory system. We also know that if you’re a premature baby and have lung development issues as a child, when you’re an adult and you’re exposed to the smoke you have increased symptoms compared to someone who was not born prematurely.
The other groups would be those with chronic respiratory and cardiac conditions, such as premature babies, pregnant women and their fetuses, and other types of populations that may have more difficulty obtaining resources, sheltering from the smoke, or implementing any type of mitigation strategies, whether due to lower income, a language barrier, access to health care, things like that.
Q: How can people protect themselves both outdoors and indoors?
A: I would say the first thing is to know what your air quality is. Some people go by just what they’re smelling which you really shouldn’t do. You can cheaply purchase an indoor air monitor, or sometimes they come on air purifiers. You can look on the internet to find out what your outdoor air quality is, noting that it does vary throughout the day. That’s something everybody could do.
If you monitor your indoor air quality and find it could be improved then, if you have the resources, an air purifier or creating a clean air room are two things that are recommended. In general, if you’re able, don’t go outside, and certainly don’t go outside and exercise. [If you do go outside] an N95 mask will filter the PM2.5 if they’re properly sealed but they don’t filter gases, and there are gases in the smoke that, ideally, should not be inhaled. Protection from the gases require a P100 or N100 respirator, rather than a N95 mask.
Be prepared if there’s any chance of being evacuated. I think it’s good that everybody in the household has at least a backpack ready to go with all their essential medicines and everything else that they need short term.
Q: What are some symptoms of smoke exposure? What should people do if they’re worried?
A: It is typical for people to complain of things like burning, tearing eyes, a sore throat, headache. There’s been studies that shown you have an increase in itching and eczema-type problems. For those milder type of symptoms, [they may] resolve when you go indoors and take a shower and get the particulate matter off. If they don’t resolve, then I would suggest reaching out to your primary care doctor. But for the more critical [symptoms], such as respiratory complications or cardiac symptoms, I would reach out sooner to your primary care doctor, or the ER if necessary, because we do know that within two hours of smoke exposure in a community there’s an increase in ambulance calls for both respiratory and cardiac outcomes. So it is possible that someone could immediately have some type of more dire symptom from inhaling [smoke]; it does not take days and days of exposure.
The level of smoke exposure that’s going to cause symptoms is really going be individual-dependent. And anything that is alarming, definitely call your primary care doctor. If symptoms are severe or progressing quickly, especially if it involves the respiratory system, or your heart, go to your nearest ER. Don’t brush it off and don’t assume that everybody is going to experience the toxicity to the same degree.
