Let’s begin with the broad strokes. How should people be thinking about this smoke?

Dominici: I think the way to think about it is not to be overly panicking, but maybe it’s a day to not spend hours outside exercising. For people that have compromised immune systems or existing respiratory or cardiovascular diseases, it would be good to limit outdoor exposure as much as possible. So don't panic but be cautious.

What is this smoke made of? What kind of particles are you concerned about?

Humphrey: Smoke from wildfires is a complex mixture of things. The thing about wildfires is they can burn anything. If a house is burning, for example, you have really complex mixtures of whatever is in that house that’s going into the air.

The one that we really worry about is the fine particles, which are known as PM 2.5 (i.e. particles smaller than 2.5 micrometers). They’re very little particles that people breathe in which have really significant impacts on heart and lung function, particularly in people who have chronic health conditions. But the impacts are still significant for people who are healthy previously and have no underlying health problems. It can cause coughing, wheezing, difficulty breathing, eye irritation, and short-term issues with lung function, even in people who don’t have any previous problems with their lungs.

Dominici: It’s not like walking by, for example, a construction site. You can see that dust, and those are not small particles. Those are coarse particles that make you cough or sneeze or bring tears to your eyes. That’s actually good, because you’re basically filtering them out. But these small particles, you don’t feel them. They penetrate very deep into the lungs, and then they cause inflammation that makes our immune response less effective.

How long do those effects last for?

Dominici: We know that these exposures to high-level fine particulate matter have both an immediate effect and a very acute effect. So we see an increase in, for example, hospital admissions, which go up the same day and the day after. But there have also been lots of studies that have documented that this effect can last for a very long time. We see chronic effects including effects on cognitive function like an exacerbation of dementia and Alzheimer's disease.

What should people do on days like today?

Humphrey: The first thing we would say is stay inside, shut your windows, stay away from the smoke, maybe buy an air purifier, exercise indoors.

But one of the tricky things with giving this kind of advice is that wildfire smoke affects people who are from disadvantaged socioeconomic communities more predominantly. And those are often the people that can't do the things that we would recommend to protect their health. For instance, many people have to go out to work or may be sleeping rough or have housing insecurity, and they don't have access to well-structured houses that protect them against wildfire smoke. So there's a real inequity there about the ability for people to follow the advice to keep themselves safe.

How should parents (of pets and children) or people with pre-existing conditions prepare for days like this?

Dominici: You can totally take your dog for a walk or your kid to the playground, but if your child has asthma that’s something to watch out for. Maybe don’t spend hours outside, and make sure you have their asthma medications. People with pre-existing conditions should contact their primary-care physicians and discuss if they should potentially change their medication dosage to make sure their exposure to smoke doesn’t exacerbate whatever problem they have.

Humphrey: We’re seeing health impacts at levels below what the EPA recommends as safe levels of PM 2.5 exposure, so when our apps say “sensitive people” it’s probably actually a message for all of us. It’s important, I think, for people who call themselves healthy to understand that you can be a marathon runner and any exposure to wildfire smoke is going to have some kind of impact on you.

Does wearing a mask help?

Humphrey: It’s very similar to COVID, so cloth masks and surgical masks offer some protection, they’re better than nothing, but they’re not as good as N95 masks. We’d recommend a really high-quality mask like an N95 because it does filter out those very, very tiny particles and offers really good protection.

Do you think COVID has made us better prepared to deal with the effects of wildfire smoke?

Humphrey: I think we have the tools. What’s missing is education. So many people have access to air quality data, it’s on an app or on the internet, but they need more education about what to do with it. I’m very, very concerned with the socioeconomic inequities in particular. It’s a lot of the same issues as COVID: All of these issues are really, really hard to solve but are part of this whole piece.

Dominici: In a certain way, COVID has been a wake-up call. We are much more cautious about what’s in our air. I think it’s always important to keep in mind that when we’re talking about the health effects, we have to really understand that they’re a manifestation of the climate crisis. It’s not something we’re going to see in the future. It’s something that’s happening right now.