THREAD: 19 Tips for a DIY mask fit test to reduce your risk of #COVID19.
H/t @amandalhu & @__philipn__
What did I miss?
Fit-testing Tip #1: Keep it Simple.
Get a nebulizer (usually $30-40) & some 3M FT-32 Bitrex solution ($24).
Fit-testing Tip #2: Taste the Failure.
Use the nebulizer to spray the bitrex solution (barely visible). Breathe through your mouth. If you taste it, there’s a mask leak.
"It’s not rocket science," as @CorsIAQ likes to say.
Fit-testing Tip #3: Spray at Problem Areas.
I use the nebulizer to spray bitrex fit-testing solution all around the nose bridge, by both cheeks, and under the chin.
You’ll quickly taste a leak.
Fit-testing Tip #4: Go Hoodless.
Do what ya wanna, but for DIY fit testing, the method above works fine w/o the hood.
I bought a hood – overpriced! Plus, the goal is to get as many people as possible fit testing. Many would find them off-putting or feel claustrophobic.
Fit-testing Tip #5: Don’t Test around Maskless People/Animals.
After reinstalling a new filter on my Flo Mask, I did a fit test while my son was having a bath. He started coughing. For a moment, I worried he had COVID.
Put 2&2 together, cranked up the HEPA & gave him juice.
Fit-testing Tip #6: Have a Beverage Handy.
You’re testing for leaks. You will find some. The bitrex tastes horrible, like licking a rubber band. Have some OJ or a soda ready for after you’re done.
Fit-testing Tip #7: Share the Wealth.
Supplies cost $60 total. It takes hardly any fit-testing solution to test, so offer the opportunity to friends, family, or co-workers. You’ll help protect their health & better cocoon yourself from illness too.
I tested all 3 of my favorite N95s: the Aegle flat-fold, 3M Aura, and 3M VFlex. I could pass a fit test with each, some caveats noted later.
Fit-testing Tip #9: Select the Best N95 for YOUR Face.
If you have several masks, test and compare. Go with the winner.
For me, the 3M VFlex held up most robustly. The 3M Aura needs to be readjusted if I talk to much. The Aegle is harder to seal at the nose.
Fit-testing Tip #10: Get your best N95 to fit better.
Although the 3M VFlex most easily & robustly passed fit-testing, I realized I hadn’t been pulling it back far enough under the chin (@jasmith_yorku). I also learned how best to adjust the nose piece to get the best fit.
Fit-testing Tip #11: Elastomeric Masks beat N95s.
I tested 6 elastomeric masks. I hate the word “elastomeric.” It’s alienating.
They’re just non-disposable, reusable masks. Great seal. All outperformed my disposable N95s when testing the limits.
Fit-testing Tip #12: Get your Elastomeric to Fit Better.
Straps can wear out or loosen over time! Filters also need to be reinstalled properly. Use fit testing periodically and when installing new filters to confirm no leaks.
Fit-testing Tip #13: Procedure Masks are a Joke.
Fit tested, fails in <0.5 sec. Air flows to the path of least resistance. Gaps poorly guard against inhaling/exhaling viral-laden aerosols.
Everybody should be using #BetterMasks, paid w/public funds.
Many KN95/KF94 masks are counterfeits, especially on Amazon. Even the city of New Orleans distributed fakes “N95s” last winter. Use fit-testing to check whether a mask is legitimate. thelensnola.org/2022/01/14/cit…
Fit-testing Tip #17: Facial Hair is a COVID Risk.
My disposable N95s start to fail fit-testing after about 2.5 days w/o shaving. My elastos make it about 3.5 days. If you’re clean-shavin, keep it clean.
If you prefer facial hair, use a mask-safe cut, or know the risk.
Fit-testing Tip #18: DBAA.
No, fit-testing is not REQUIRED for masks to “work.”
It’s about improving safety on the margins (5-10%) and especially for the most dangerous prolonged contexts. osha.gov/laws-regs/stan….
FYI, I have no conflicts of interest, such as investing in one of the companies mentioned.
I’m a psychologist just trying to help people understand COVID mitigation tips I didn’t know a year ago so maybe you can reduce your lifetime number of cumulative SARS-CoV-2 infections.
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U.S. CDC numbers just released. Good news (for those not in Louisiana). "Only" a 5% national increase.
2025 has closely tracked with summer 2023 transmission. A 12-13% increase would have been expected based on those numbers. That said...
real-time data have been prone to retroactive corrections. This is frustrating, of course, because it leaves people making decisions based on data that are only of good quality when 2 weeks old.
If we saw a 12% increase this week, I'd say look at 2023 for a glimpse...
at the future. Instead, I would consider these plausible scenarios:
🔹Wave still similar to 2023
🔹Later wave with schools more implicated
🔹Something temporarily much better
COVlD is surging in 7 states, according to the CDC.
🔹Hawai'i (Very High)
🔹California (High)
🔹Nevada (High)
🔹Texas (High)
🔹Louisiana (High)
🔹Florida (High)
🔹South Carolina (High)
2. PMC COVlD Dashboard, July 21, 2025 (U.S.)
Western surge:
🔹California: 1 in 63 actively infectious, much higher in LA & Bay areas
🔹Hawai'i: 1 in 35 actively infectious
🔹Nevada: 1 in 63 actively infectious
These are wastewater derived estimates, not from individual tests
3. PMC COVlD Dashboard, July 21, 2025 (U.S.)
Southern surge:
🔹Texas: 1 in 56
🔹Louisiana (New Orleans): 1 in 65
🔹Florida: 1 in 66
🔹South Carolina: 1 in 71
Again, wastewater estimates (wise indicator), not individual testing (low-quality data).
We estimate 1 in 148 Americans are actively infectious. This equates to 2.3 million infections/week, expected to result in >100,000 new #LongCOVID conditions & >800 deaths.
A room of 100 people is a coin toss of an exposure.
2) PMC COVlD Dashboard, July 14, 2025 (U.S.) 🧵
Transmission (red) is closely tracking the path of 2 years ago (yellow). However, the incoming data are spotty. >20% of CDC states have limited/no data, & Biobot hasn't reported in weeks.
Could be MUCH worse or slightly better.
3) PMC COVlD Dashboard, July 14, 2025 (U.S.) 🧵
Our model formalizes the mathematical assumptions in those predictions. If transmission follows what we know in terms of how waves grow or slow generally and historical patterns, this is what we'd expect.
The spottiness of the current real-time data reduce precision substantially. Retroactive corrections can make the forecast jump around from better to worse from one week to the next. Expect the worst. Hope for the best.
🌍Want to track COVID transmission accurately worldwide?
This PMC thread walks you through leading dashboards with information more up to date than WHO & EU directories.
🧵 1/
The Pandemic Mitigation Collaborative (PMC) Dashboard provides weekly COVID updates for the U.S., using wastewater surveillance derived case estimation models and analytic forecasting.
Our international directory includes official government dashboards & those developed by citizen scientists.
We exclude countries that have stopped reporting in the past 2-12 months even if on EU or WHO lists. We also exclude low-quality data from opt-in testing programs.
🧵 3/
🔥Biggest uptick since Jan
🔥1 in 167 actively infectious
🔥>2 million weekly infections
🔥700-1,200 resulting excess deaths from weekly infections
Track transmission closer to home w/our new state & international resources 👇
🧵1/6
PMC COVlD Dashboard, Jun 23, 2025 (U.S.)
🔹With >90% probability, we have entered the 11th COVlD wave.
🔹In a room of 50 people, there is already a 1 in 4 chance of an exposure.
🔹We expect nearly 15 million infections in the next month, and rising.
🧵2/6
PMC COVlD Dashboard, Jun 23, 2025 (U.S.)
We continue to expect transmission to break 500,000 daily infections in the U.S. around July 9th.
This is the same prediction as last week, as the forecast was dead on. Yet, there is considerably uncertainty around this timing.