Masks. Just saying the word probably triggered something in you; either “finally, someone gets it” or “here we go again.” 

Here’s the thing: I’ve spent the last few years watching really smart people dig into absolutist positions on both sides of this debate. Masks either save lives or they’re completely useless. You’re either with science or against it. No middle ground allowed. But you know me, I live in the nuance. And when it comes to masks, there’s a lot more nuance than most people want to admit. 

Let me share something that might surprise you: when you look at the actual size of virus particles compared to the pores in an N95 mask, those particles can absolutely pass through. And when you dig into the gold-standard research—the kind we’d demand before approving a new drug—the results are far less impressive than the public messaging suggested. 

Does this mean masks are useless? No. Does it mean they’re the silver bullet we were told? Also no. 

In fact, I've been known to sport the accessory from time to time. If you've been following me for some time, you'll recall the "Vitamin D For Everyone Campaign", where Meghan and I donned facial protection as we handed out free vitamin D. 

"Vitamin D For Everyone" Campaign

Meghan and Josh giving out free vitamin D in 2021

Anywho, let’s dig in. 

SIZE MATTERS 

Check out this chart. It shows the sizes of various bugs we can spread through breathing, and whether they can theoretically slip through an N95 mask based on size alone: 

Here’s what jumps out: SARS-CoV-2 particles clock in at 0.06 to 0.14 micrometers.[1,2] N95 respirators are designed to filter particles down to 0.3 micrometers.[3] 

Do the math. These viruses are 2-5 times smaller than what N95s are built to catch. 

Now, you might be thinking, “But Josh, doesn’t the mask still block some of them?” Maybe. And here’s where things get interesting, or frustrating, depending on your perspective. 

WHAT THE BEST RESEARCH ACTUALLY SHOWS

When it comes to masks and COVID, we don’t have dozens of these trials. We have two. Just two. 

The Danish DANMASK-19 study was the first.[5] Nearly 5,000 people participated. Half received masks and instructions to wear them, while the other half didn’t. The result? No statistically significant difference in COVID infection rates between the groups. 

The Bangladesh study was bigger—over 340,000 people across 600 villages.[6] This one did show a reduction: 9% overall, 11% in villages that got surgical masks specifically. That’s… modest. And that was with a massive community-wide intervention that tripled mask wearing from 13% to 42%. 

Now here’s what really matters: In 2023, the Cochrane Collaboration—basically the gold standard for medical evidence reviews—analyzed 78 randomized trials on masks and respiratory viruses.[4] Their conclusion for community mask wearing? 

“Probably makes little or no difference.”[4] 

Not “definitely doesn’t work.” But also not “definitely works.” It’s that uncomfortable middle ground where most real science lives. 

Recent analysis puts it even more bluntly: “Randomized clinical trials of masking for prevention of COVID-19 and other respiratory viruses have so far shown no evidence of benefit (with the possible exception of continuous use of N95 respirators by hospital workers).”[7] 

So we’ve got a disconnect. The theory says masks should work. The laboratory tests show they can block particles. But the real-world trials? They’re not giving us the clear signal we were promised.

THE STUFF NOBODY TALKS ABOUT

While everyone’s been arguing about whether masks work, there are some legitimate concerns that were completely drowned out. These aren’t conspiracy theories; they’re published research that deserves attention. 

1. You’re Breathing Plastic 

Most disposable masks are made from polypropylene, a synthetic plastic. And yes, you’re inhaling tiny pieces of it when you breathe through them. 

Studies have found:[8,9,10]

• Surgical masks shed particles ranging from 300 nanometers to 2 millimetres while you’re breathing 
• The plastic release peaks after about 8 hours of wear 
• The inner layer (usually polyethylene) sheds more microplastics than the middle and outer layers combined

We don’t know what chronic microplastic inhalation does long-term. We do know that microplastics have been found in human lungs and linked to certain lung abnormalities.[9,10] But we’re missing the long-term safety data. 

Bottom line: If you’re wearing masks regularly, change them often.[11] The longer you wear them, the more plastic fibres they shed. 

2. The CO₂ Question 

When you exhale into a mask, some of that carbon dioxide gets trapped between your face and the mask. You breathe it back in with your next breath. 

A meta-analysis of 29 studies found CO₂ levels in your breathing zone jump from 500-900 ppm (normal) to 2,150-2,875 ppm with a mask.[12,13]

For comparison purposes, this is what my CO₂ meter reads right now in my office as I'm sitting here writing this. It can get into the 900s and slightly above when the door is closed. 

These levels stay below the NIOSH danger threshold for short-term exposure.[13] But here’s what we don’t know: what happens with chronic, low-level CO₂ exposure over months or years, especially in kids with developing brains?[14] 

Symptoms of elevated CO₂ include:[12,15]

• Headaches 
• Brain fog and concentration issues 
• Fatigue 
• Dizziness 
• Increased heart rate

For most healthy adults wearing a mask for an hour? Probably fine. For healthcare workers in N95s for 12-hour shifts, or kids in masks all day at school? That’s a different calculation. 

3. The Kids Question 

This is where things get emotional, so let’s stick to what the research actually shows. 

Language Development 

Babies learn to talk by watching mouths move.[16] They’re little lip-reading machines, and the ones who do it more have better vocabularies later.[16] When everyone’s masked, they miss those visual cues.[17] That said, blind kids learn language just fine, so clearly it’s not the only way.[18] 

Reading Emotions 

Multiple studies confirm that masks make it harder for kids to read emotions, especially sadness and happiness.[19,20] Brain imaging shows that kids’ brains have to work harder to process masked faces, and this effect is amplified in stressed kids.[21,22] The 3-5 year age group struggles the most with this.[19] 

The Trade-Offs 

Here’s the reality check: Schools with mask mandates stayed open more.[23] School closures demonstrably harmed kids’ mental health.[18,23] No long-term studies have shown developmental delays from masks themselves.[24] And kids are also breathing microplastics and CO₂ just like adults, but with developing systems that might be more vulnerable to these exposures.

4. The Fit Problem

Most people don't wear masks correctly. Studies show that even healthcare workers, who receive training, have fit issues with extended wear. For children, the problem is worse: masks designed for adults create gaps around the edges, upper bridge, and sides of the face. Kids fidget with masks, adjust them constantly, and often wear them below their nose without realizing it.

If you're relying on a mask for protection in a high-risk scenario, it needs to be fitted properly and worn correctly throughout.

5. A Critical Caveat!

Nearly everything in this post pertains specifically to N95 respirators—yet most people wore cloth or surgical masks instead. The effectiveness gap is substantial: N95s filter ≥95% of particles when properly fitted, while surgical masks filter far less, particularly for aerosols. This distinction fundamentally changes the risk-benefit calculation for the vast majority of mask wearers.

SO… WHAT SHOULD YOU DO?

I’m not going to tell you to wear a mask or not wear a mask. That’s not my job, and frankly, it depends on your specific situation. What I will tell you is this: 

The evidence shows:

• On pure particle size, viruses are small enough to theoretically pass through mask material, but bacteria and fungi might be blocked
• The gold-standard randomized trials show inconsistent results—some modest benefit in some populations, no clear benefit in others 
• The highest-quality evidence review (Cochrane) says the data is uncertain 
• Even when benefits are shown, they’re modest, not dramatic

The conversation we’re not having:

• Masks expose you to microplastic inhalation (especially with prolonged wear) 
• CO₂ rebreathing is real, even if usually below danger thresholds 
• There are legitimate developmental concerns for kids, though the pandemic itself probably caused more harm than masks did 
• We’re missing long-term safety data on chronic mask use

What makes sense:

• Make decisions based on your risk profile, not headlines 
• If you’re wearing masks regularly, change them frequently 
• Take mask breaks when you safely can 
• For kids, maximize face-to-face unmasked time at home 
• Question anyone—on either side—who speaks in absolutes

The science of masks is messy. It doesn’t fit into a neat “works” or “doesn’t work” box. The real-world evidence is underwhelming compared to what we were told. But there are situations where they might still make sense. 

The key is making informed decisions with accurate information, not perfect information (because we don’t have it), but honest information about what we actually know and don’t know. 

That’s where I think real health wisdom lives. Not in the extremes, not in the absolutes, but in the thoughtful, evidence-based middle ground where we can acknowledge uncertainty without losing our minds about it.

References

1. Laue M, Kauter A, Hoffmann T, et al. Morphometry of SARS-CoV and SARS-CoV-2 particles in ultrathin plastic sections of infected Vero cell cultures. Sci Rep. 2021;11:3515.
2. Zhu N, Zhang D, Wang W, et al. A novel coronavirus from patients with pneumonia in China, 2019. N Engl J Med. 2020;382(8):727-733.
3. Rengasamy S, Eimer B, Shaffer RE. Simple respiratory protection—evaluation of the filtration performance of cloth masks and common fabric materials against 20-1000 nm size particles. Ann Occup Hyg. 1998;42(2):128-132.
4. Jefferson T, Dooley L, Ferroni E, et al. Physical interventions to interrupt or reduce the spread of respiratory viruses. Cochrane Database Syst Rev. 2023;1(1):CD006207.
5. Bundgaard H, Bundgaard JS, Raaschou-Pedersen DET, et al. Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers: a randomized controlled trial. Ann Intern Med. 2021;174(3):335-343.
6. Abaluck J, Kwong LH, Styczynski A, et al. Impact of community masking on COVID-19: a cluster-randomized trial in Bangladesh. Science. 2022;375(6577):eabi9069.
7. Cody MJ, Horve PF, Leung MHY, et al. Masking for COVID-19 and other respiratory viral infections: implications of the available evidence. BMC Infect Dis. 2024;24:417.
8. Li L, Zhao X, Li Z, Song K. COVID-19: Performance study of microplastic inhalation risk posed by wearing masks. J Hazard Mater. 2021;411:124955.
9. Patrício Silva AL, Prata JC, Duarte AC, Barcelò D, Rocha-Santos T. Disposable face masks: a direct source for inhalation of microplastics. arXiv preprint. 2023;arXiv:2308.16295.
10. Cao J, Shi Y, Yan M, et al. Face mask: as a source or protector of human exposure to microplastics and phthalate plasticizers? Toxics. 2023;11(2):87.
11. Zhu K, Gong W, Wang Z, et al. Assessment of inhalation exposure to microplastic particles when disposable masks are repeatedly used. Environ Pollut. 2024;342:123079.
12. Sahebi R, Khorshidi F, Mahmoodi S, et al. The influence of N95 and surgical masks on carbon dioxide levels: a comprehensive systematic review and meta-analysis. Heliyon. 2024;10(16):e35626.
13. Rhee MSM, Lindquist CD, Silvestrini MT, et al. Carbon dioxide increases with face masks but remains below short-term NIOSH limits. BMC Infect Dis. 2021;21(1):354.
14. Kisielinski K, Giboni P, Prescher A, et al. Possible toxicity of chronic carbon dioxide exposure associated with face mask use, particularly in pregnant women, children and adolescents. Heliyon. 2023;9(2):e14117.
15. Sinkule EJ, Powell JB, Goss FL. Evaluation of N95 respirator use with a surgical mask cover: effects on breathing resistance and inhaled carbon dioxide. Ann Occup Hyg. 2013;57(3):384-398.
16. Lewkowicz DJ, Hansen-Tift AM. Infants deploy selective attention to the mouth of a talking face when learning speech. Proc Natl Acad Sci USA. 2012;109(5):1431-1436.
17. Birulés J, Bosch L, Brieke R, Pons F, Lewkowicz DJ. Bilingualism modulates infants’ selective attention to the mouth of a talking face. Psychol Sci. 2019;30(10):1469-1479.
18. Ruba AL, Pollak SD. Children’s emotion inferences from masked faces: implications for social interactions during COVID-19. PLoS One. 2020;15(12):e0243708.
19. Gori M, Schiatti L, Amadeo MB. Masking emotions: face masks impair how we read emotions. Front Psychol. 2021;12:669432.
20. Carbon CC. Wearing face masks strongly confuses counterparts in reading emotions. Front Psychol. 2020;11:566886.
21. Waizman Y, Griner D, Palumbo I, et al. Neural processing of facial emotion under face masks: an fMRI study. Emotion. 2024. Advance online publication.
22. Carragher DJ, Hancock PJ. Face masks disrupt holistic processing and face perception in school-age children. Cogn Res Princ Implic. 2022;7(1):9.
23. Donovan CV, Rose C, Lewis KN, et al. SARS-CoV-2 incidence in K-12 school districts with mask-required versus mask-optional policies—Arkansas, August-October 2021. MMWR Morb Mortal Wkly Rep. 2022;71(10):384-389.
24. Charney SA, Camarata SM, Chern A. Potential impact of the COVID-19 pandemic on communication and language skills in children. Otolaryngol Head Neck Surg. 2021;165(1):1-2.