Why It Works

I’m one of those people who has to see something work before I understand how it works. I mean, I knew hand-washing and social distancing worked to slow the spread of the coronavirus that causes COVID-19. I believed our scientists and healthcare workers. But how do you see something as small as a virus that is hundreds of times smaller than other things(1) you can only see with a microscope?

Luckily, I’m one of those people who also thinks in metaphors. What if the infectious dose of the coronavirus was a like drop of food coloring? Here is a fun little experiment you can use to show kids why hand-washing is important—and get the visual yourself. You’ll need food coloring, an spoon, a clear pint jar, and a clear quart jar. Oh! And an eyedropper would help.

One jar will do fine. Image by  @Debduca via Twenty20

Before getting started, let’s talk about spreading the disease. You’ve probably heard that the virus can “live” on hard surfaces for days and that it travels in droplets for more than six feet. One study showed that a sneeze can propel the virus for up to sixteen feet. So it’s important to understand that getting exposed to the virus does not mean you’ll die. It doesn’t even mean you’ll get sick or become a carrier. To get sick, you need to acquire enough of the virus to overcome your immune system, what scientists call an “infectious dose(2)2.”

Washing your hands and keeping physically distant from others reduces the
dose when you are exposed. And that brings us back to my nifty little activity. We’re going to pretend that one drop of food coloring is an infectious dose of the virus. If you put a drop of food coloring on the back of your hand, you’ll get most of it off. If you drop it on a hard surface, it just sits there waiting to be picked up by a living thing. It doesn’t live there. Viruses aren’t really alive. They are just stray bits of DNA that invade other living cells and hijack them to make more copies of the virus. Here’s where the food color analogy breaks down. Food coloring will probably stain whatever you put it on. Unless it is absorbed into another living organism, the virus will eventually fall apart and disappear.

Washing hands is always good! Photo by @vinnikava via Twenty20

Both hand-washing and physical distancing work the same way. The further the virus travels from its source, the more spread-out it gets. This process is called diffusion.

Let’s put a drop of the food coloring into the empty pint jar. It just sits there waiting for a victim to come along. But we’re going to interfere with its plans. We’re going to make it more diffuse by filling the pint jar with water, just as if we washed our hands to get the virus off.

What happens next? Image by Justin Lau.

Wait! Doesn’t that just help it spread more? Well, kind of. It spreads out more, but there is less of it in any given place. See how none of the water is clear, but neither is the virus as dark as it was when it was a drop sitting at the bottom of the jar. The virus is in more places, but it is spread thinner in all of those places. Now you’d have to drink that whole pint to get the same amount of virus as if you had put a drop on your tongue. If you stick your finger in the solution, it comes back a lot less stained than if you had touched the drop in the bottom of the jar. It’s spread out more, but it takes a lot more contact to get an infectious dose and contract the disease or become a carrier.

If you pour everything from the pint into the quart, the “virus” gets even more diffuse because some of it gets left in the pint. If you wash your hands again—or fill the quart jar with water—it gets even more spread out and less infectious. Now if you repeat this process with a gallon container or a five gallon bucket…you get the point.

Masks work in a similar manner by creating a barrier that reduces the amount of the virus that gets through.

If we all work together by washing our hands, keeping our distance, and
wearing a mask, we can all live happily together. But it only takes one person to screw things up for everyone else. One person without a mask can infect lots of people. Let’s all do our best to keep each other safe.

My wife likes to coordinate her masks with her outfits…and hair.

(1) https://abcdust.net/how-large-is-a-corona-virus-virion-compared-to-the-mp10-2-5/
(2) https://www.statnews.com/2020/04/14/how-much-of-the-coronavirus-does-it-take-tomake-you-sick/