WHAT WAS CLAIMED
CDC advice on wildfire smoke shows masks are “totally useless” against COVID.
OUR VERDICT
Misleading. A graphic accompanying the claim misrepresents how COVID is spread.
AAP FACTCHECK - A misleading infographic is being used to suggest the Centers for Disease Control (CDC) in the US has "accidentally" admitted face masks are "totally useless" against COVID.
However, the graphic not only misrepresents the size of smoke particles but also misleads on how COVID particles are spread.
The CDC told AAP FactCheck masks are effective and that different types offer varying levels of protection.
The organisation's website notes efficacy between 10 and 99 per cent across 11 different masks.
How well a mask fits is a major factor in how effective it is: "Gaps can let air leak in and out," a CDC spokesperson said.
The claim first appeared in 2020 following a genuine CDC Facebook post, during California's August Complex Fire, advising cloth masks used to slow the spread of COVID shouldn't be relied on as protection against smoke.
Although previously debunked by AFP and Health Feedback, the claim has now resurfaced amid the latest wildfires.
One of the recent Facebook posts shows a diagram with a line-up of particles labelled in order of increasing size as "Coronavirus", "Bacillus Bacteria", "PM2.5", "Red blood cell" and "SMOKE".
Below the image is the 2020 CDC caption, which reads: "Cloth masks that are used to slow the spread of COVID-19 offer little protection against wildfire smoke. They do not catch small particles found in wildfire smoke that can harm your health. Limit your time outside when it's smoky."
Large overlaid text reads: "CDC accidentally ADMITS masks are totally USELESS."
The post has been shared by Mike Adams, aka HealthRanger on X and the founder of Natural News, a website known for publishing false health information.
"So how is it that N95 masks don't work on SMOKE particles, but we are told they DO work on coronavirus particles?" Mr Adams' post reads.
"'The science' is fiction... masks are a FRAUD."
While the diagram's origins are unclear, it has been reproduced multiple times online with variations on the wording.
The largest particle is usually labelled as PM10 (particulate matter with a diameter of 10 microns), not as smoke.
Health science expert Catherine Clase pointed AAP FactCheck to McMaster University research that shows how different types of masks offer varying levels of protection against a range of aerosols.
CDC-approved respirators, including the N95 mask, offer the most protection against COVID-19, blocking up to 99 per cent of submicron (less than one millionth of a metre) aerosol particles when fit-tested.
The filtration of surgical and two-layer cloth masks is lower, but they still block 50 to 70 per cent of aerosols.
Professor Clase said the diagram is misleading because aerosols from smoke don't just come in one size and, while the virus that causes COVID is small, it travels through the air via larger particles such as mucous and "cellular debris".
At 0.01 micron (a millionth of a metre), the COVID-19 virus is usually carried on the larger respiratory aerosols produced by breathing, sneezing, coughing and speaking.
Wildfire smoke, meanwhile, contains harmful aerosols of varying sizes, such as PM2.5, which can make their way into the respiratory system, leading to short- and long-term health risks.
Prof Clase said: "You can draw smoke or respiratory particles at any size you like, from 0.01 microns to 100 microns.
"Smoke aerosols can be big or small. COVID circulates in the air in respiratory particles that can be big or small. Drawing COVID at 0.1 micron (which should be 0.01 micron, actually) and labelling PM10 'smoke' is clearly a misrepresentation of the data."
Harmful gases that are not blocked by masks or respirators - such as carbon monoxide, ozone and nitrogen oxides - are also released from wildfires.
"It's disappointing that people paint the picture that they want to see rather than observing the details and trying to understand the nuance," environmental health science researcher Laura Kwong said.
"To protect yourself against wildfire smoke, wear a well-fitting respirator," Dr Kwong advised.
The CDC's wildfire information page recommends a respirator mask if people need to go outside during a fire.
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