Airborne vs. Aerosol vs. Droplet: What's the Difference?

Victor J. Blue/Stringer/Getty Images
Victor J. Blue/Stringer/Getty Images

This article was updated on July 13 with new information from the World Health Organization.

COVID-19 has introduced several new terms to the national lexicon. In addition to phrases like social distancing, self-quarantine, and N95 respirator, you may have seen the word airborne popping up more in recent weeks. It usually appears in discussions concerning how the novel coronavirus that causes COVID-19 is transmitted—a question that's still debated by health experts. So what exactly does it mean when a pathogen is airborne, what do droplets and aerosol have to do with it, and which of these terms apply to the new coronavirus?

What are droplets?

We know that there are at least two ways to catch the new coronavirus: by coming in close contact with infected individuals and touching contaminated objects and surfaces. In both cases, the root of the transmission is often a cough or sneeze. When someone with COVID-19 coughs—which is a common symptom of the disease—they send a spray of mucus and saliva droplets flying from their mouths. These tiny, sometimes invisible droplets, measuring between five and 10 micrometers in diameter, contain particles of the virus. Coughing into a shirt sleeve or mask can catch a lot of these droplets, but with nothing to block them, many will land on objects and people in the immediate vicinity. This is why a sick person is more likely to infect more people standing elbow-to-elbow with them in crowded subway car than they are keeping a 6-foot distance from others in a spacious park.

You don't need to be touching someone to contract coronavirus from them. If someone is standing directly behind you in line at the grocery store, they can infect you through the droplets in a sneeze or cough. But while these droplets technically travel through the air, that doesn't automatically make COVID-19 an airborne disease—at least not according to the definition of the word used by health officials. In order to understand what airborne really means, you need to know about aerosols.

What are aerosols?

Saliva and mucous droplets are heavier than air, which means gravity starts pulling them—and whatever viral particles they contain—towards the ground as soon as they leave someone’s body. By the time someone walks out of a room, any droplets they may have emitted have likely already settled on the floor or nearby surfaces—so usually, you don’t need to worry about breathing in those droplets if you’re social distancing correctly.

Aerosols are a different story. They form when smaller droplets evaporate faster than they fall to the ground, leaving nuclei measuring less than five micrometers in diameter. Without heavy liquids dragging them down, virus particles from these evaporated droplets are able to float through the air for up to half an hour. When a virus travels via aerosols, it’s possible to contract it by entering an empty room that a sick person was in several minutes earlier. This transmission via free-drifting aerosols is how the World Health Organization defines an airborne disease.

Is the new coronavirus airborne?

The WHO updated its scientific brief in July to say that airborne transmission of the new coronavirus appears to be possible. Citing three studies of infections in a gym, a choir practice, and a restaurant, WHO stated, "short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons, cannot be ruled out."

Though there may be a chance of the novel coronavirus wafting in ambient air, it's not unsafe to open a window or go outside. Airborne viruses are more likely to spread in rooms with poor ventilation than they are outdoors, so allowing air to circulate in your home can actually help prevent the spread of disease. Plus, getting fresh air and exercise is important for staying mentally and physically well in stressful situations.

When leaving the house, just keep some safety precautions in mind. Maintain at least a 6-foot distance from others to protect yourself from droplet transmission, and wash your hands thoroughly after touching surfaces that may be contaminated. Wearing an N95 respirator is the best way to prevent airborne infection, but because supplies are limited, new masks should be reserved for especially vulnerable people like healthcare workers. Homemade cloth masks and surgical masks aren’t built to filter out smaller airborne particles, but they can stop larger droplets from splashing onto your face, and just as importantly, stop infected wearers from spreading droplets to others.

Mental Floss's Three-Day Sale Includes Deals on Apple AirPods, Sony Wireless Headphones, and More

Apple
Apple

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Apple

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Sony

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Sony

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Martha Stewart

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Jashen

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Evachill

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Gourmia

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Townew

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Noerden

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Prices subject to change.

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Absentee Ballot vs. Mail-In Ballot: What’s the Difference?

Liliboas/iStock via Getty Images
Liliboas/iStock via Getty Images

Since you mail in an absentee ballot, it seems like mail-in ballot is just a convenient alternative for people who always forget the word absentee. And though the terms are often used interchangeably, there is technically a difference.

Up until the Civil War, American voters were generally required to vote at their local polling stations in person. But when states realized this would prevent hundreds of thousands of soldiers from voting in the 1864 presidential election, they started passing laws to let them send in their ballots instead. As The Washington Post explains, state legislatures have since broadened these laws to include other citizens who can’t make it to the polls on Election Day: people who are traveling, people who have disabilities, people attending college away from home, etc. Because these voters are all physically absent from the polls for one reason or another, their ballots are known as absentee ballots.

Some states require you to meet certain criteria in order to qualify for an absentee ballot, while others don’t ask you to give a reason at all (which is known as “no-excuse absentee voting”). Since this year’s general election is happening during a pandemic, many states have temporarily adopted a no-excuse policy to encourage everyone to vote from home. But even if you don’t need to provide an excuse, you do usually need to request an absentee ballot.

According to Dictionary.com, mail-in ballot is a more general term that can refer to any ballot you send in. It’s often used when talking about all-mail voting, when states send a ballot to every registered voter—no request necessary. Oregon and a few other states actually conduct all elections like this, and several other states have decided to do it for the upcoming presidential election. But even though you don’t have to send in an application requesting a mail-in ballot in these situations, you do still have to be registered to vote.

Because voting processes are mostly left up to the states, there’s quite a bit of variation when it comes to what officials call ballots that you don’t cast in person. You could see the term mail-in ballot—or vote-by-mail ballot, or advanced ballot, or something similar—on an application for an absentee ballot, and you could hear absentee ballot used in a conversation about all-mail voting.

No matter what you call it, you should definitely mail one in for this election—here’s how to do that in your state.