Read on Twitter
In case you did not know this before, apologies for bringing you this visual. There are likely millions of airborne particles around you, at this very moment. Not all of them deserve a similar level of concern though. A 
2/n This is of course inspired by the ongoing discussions on if a virus that is not as infectious as measles can or cannot be airborne or can it be airborne under "special circumstances" 
3/n Pollens are airborne. They trigger seasonal allergies. Not everyone is allergic though. I was not allergic till my late teens and later became mildly allergic.
4/n Pet dander is airborne You can even find it in places where the animal itself is not present. Again, it also causes allergic reactions and nasal congestion
5/n Particulate matter is airborne. You must have heard about PM10 and PM2.5 as indicators of outdoor air quality. Acute and chronic exposure to PM is supposed to have different mechanisms of effect. They can cause both respiratory and cardiovascular effects
6/n Ultrafine particles (UFPs) are airborne. They likely constitute nearly 90% of all airborne particles. Smaller than 0.1 microns, they can be inhaled and then make their way into pretty much any organ system
7/n Mold spores are airborne. They can be allergenic, pathogenic, and/or toxigenic
8/n Lead is airborne. It has a cumulative effect on long-term health and early exposures could mean trouble later in life.
9/n By now, probably you can see where this is going. There can be a bunch of things which are airborne. Not all of them are necessarily harmful (clouds are airborne too). Those that can cause harm do so by multiple mechanisms. And not all of them harm to the same degree
10/n What is common is that they are all suspended in air. Depending on their size they can be inhaled and land up in different parts of the body. Depending on size, they can remain in air for different durations of time.
11/11 How something airborne harms us and to what extent, that does not do away the fact that they are airborne. Judging if something is airborne or no based on how infectious (harmful) it is, is putting the cart before the horse.
