Thread by @MakalMakal

I just saw a post about "If a fart can make it through underwear and a pair of jeans, how can a mask made of cloth save you from covid? Asking for a friend..[sic]" Well, firstly, thank you for the question! As a scientist (specifically a chemist, I am absolutely qualified to 1/9

answer this question! Let's consider the size of the molecules that make up the stink smell in farts. We'll focus on one particular example, as the others are similarly sized (when compared to the size of a virus). Methanthiol (CH3SH), like a number of thiol (-SH) containing 2/9

molecules, smells! When you work with it enough (as I have), it smells like incredibly intense garlic; though many would just say it smells putrid. If you want everyone to hate you, walk through a hallway carrying an open container of thiol compounds. Ask my former student 3/9

and colleagues, they all remember that day! Well, CH3SH is a rather small molecule with a diameter around 4*10^-10 m (0.4 nm, about 1.6*10^-8 inches). By comparison, viruses typically range in diameter from about 20 nm up to about 400 nm (J. Biol. Phys., 2013, 39(2), 215), 4/9

with COVID-19 being around 60-140 nm (Cell. Mol. Immun., 2020, doi.org/10.1038/s41423…). The difference in sizes of the COVID-19 virus and a common odorant in farts is 2-3 orders of magnitude (100–1000 times the diameter of the smaller methanethiol). An N95 mask is capable 5/9

of filtering 95% of a test aerosol containing average particle size of 300 nm (from the CDC: blogs.cdc.gov/niosh-science-…). Basically, an N95 mask has a tight weave pattern with multiple layers that serve as a barrier to larger structures (like viruses, or simply spittle). 6/9

While the benefits of a specific mask will depend on the fabric and construction of the mask (not to mention how it is worn), having some form of barrier between an infected individual and a healthy individual is far superior to open air allowing for the transfer of virus 7/9

(along with other matter) between those individuals. Lastly, to argue that “since I can smell a fart through a mask, there's no point in wearing a mask to protect me against viruses” is like securing a medieval castle with a gate to keep out invading horsemen, 8/9

but arguing that because roaches can still enter that there is no point in having a gate. Clearly you have not considered that the horseman is the greater threat. 9/9

Thanks to everyone who has been interacting with this thread! I realize I slipped up with one of my replies. The peeing/jeans picture is not mine. I'm not sure of the source of that particular image that was shared by someone else as a reply. Sorry for any confusion!

A follow-up for anyone interested in the science behind filtration efficiencies: pubs.acs.org/doi/abs/10.102…

Want more info? Check this article (with references, bc science). Still slinging the "masks don't help", "but the virus is smaller than 300nm", "mask material/fit", etc? I've already addressed these with citations. Cite your sources or get out. science.sciencemag.org/content/368/64…