Wildfire smoke billowing over Washington state has complicated the ways in which we keep ourselves safe from COVID-19. Smoke can diminish our immune and respiratory systems, which could make us more susceptible to contracting the virus that causes COVID-19 and could worsen symptoms for those who already have the disease.

For this week’s FAQ Friday, we’re tackling a common question about masks and wildfire smoke. We’ll also take a look at asymptomatic spread of the virus that causes COVID-19. 

Do cotton masks protect against both the virus that causes COVID-19 and also wildfire smoke? 

No. Homemade cotton masks and even surgical masks, which are now commonplace and required in many public places, don’t protect against wildfire smoke. 

While the woven fabric can block the aerosols that carry the coronavirus, tiny soot particles can still pass through, UW Medicine pulmonologist Dr. Cora Sack told The Seattle Times this week.

“What we really worry about in wood smoke are those small particles, which, when inhaled, have the ability to get deeper into the lungs,” Sack said. 

The effects of COVID-19 and wildfire smoke overlap. Both woodsmoke and COVID-19 can harm the immune and respiratory systems. 


“Stay indoors and keep your indoor air clean,” said Lacy Fehrenbach, deputy secretary of health for COVID-19 response for the state health department. “When the air is fresh, open your windows.” 

N95 respirators that fit properly do prevent fine particles from passing through, but health officials say that equipment should continue to be reserved for health care workers because it’s the most effective option for protecting against aerosol transmission of the virus that causes COVID-19 in medical settings.

And as we’ve written in previous FAQs, those N95 masks with valves aren’t an ideal option either. They protect the wearer — which is why you might have seen construction workers wearing them to avoid dust — but they let your breath out into the world, thus not protecting others from the virus if you’re infected without knowing it.

How many people who are tested have symptoms?

Washington state doesn’t report information on why someone sought testing. But this question is a good starting point to cover some interesting data. 

On recent weekdays, more than 13,000 people statewide have been tested for COVID-19. For the week preceding Sept. 1, nearly 3.3% of those tests came back positive for the virus. 

Testing data nationwide and in Washington state remains biased toward those experiencing moderate to severe symptoms of COVID-19, because someone with symptoms is more likely to seek out a test. And, particularly early on, there simply haven’t been enough test kits to randomly sample populations. 


But, the commonly known symptoms of COVID-19 — such as fever, chills, cough, shortness of breath, fatigue, muscle, body aches, headache, sore throat, congestion, nausea or diarrhea — are also associated with other ailments. Many people likely present with symptoms, only to test negative, meaning they suffered from something else. 

You might also be wondering about people who are infected with the virus, don’t know it and could be unwittingly spreading it. (People without symptoms can spread the virus.)

Scientists around the world are racing to understand “asymptomatic spread,” often looking at testing results of enclosed communities, such as tourists on cruise ships or sailors on naval vessels. 

A recent review of much of the scientific literature on the subject estimated that people without symptoms could represent 40-45% of total infections, though the science remains unsettled and this figure is likely a moving target.

And just because someone doesn’t present with obvious symptoms doesn’t mean COVID-19 isn’t changing their body. Researchers believe COVID-19 in asymptomatic patients might be causing “subclinical lung abnormalities,” which could cause “subtle deficits in lung function.” 

Seattle Times readers have submitted thousands of questions about COVID-19 and the new coronavirus that causes the disease. You can read last week’s coronavirus FAQ at st.news/faq-surfaces. If you have a question you haven’t seen addressed in The Seattle Times’ coverage, ask it at st.news/coronavirus-questions or via the form below.

Do you have questions about the coronavirus that causes COVID-19?

Ask in the form below and we’ll dig for answers. If you’re using a mobile device and can’t see the form on this page, ask your question here. If you have specific medical questions, please contact your doctor.