For most of my adult life, I didn’t own a microwave. It wasn’t a deliberate stand against convenience; I just never got into the habit of using one. Leftovers went into a pan on the stove, frozen foods into the oven, and popcorn into my ancient air popper that looks like it came free with a 1978 station wagon. Even now that there’s a microwave in my kitchen, those are usually still my first moves.
I’ve found uses for it, though. I recently discovered that it’s surprisingly handy for caramelizing onions and making brie chips, and I’m certainly not dirtying a saucepan when I need a little melted butter for dipping artichokes. My microwave is slowly making a case for itself.
Which means I’m finally spending enough time in front of it to notice the door. More specifically, the field of tiny dots between me and whatever I’m heating. Turns out they’re actually doing one of the microwave’s most important jobs.
Why do microwave doors have black dots?
If you look closely, you’ll see that those dots are actually tiny holes in a metal screen inside the microwave door. That screen is there to keep microwave energy inside the oven while still letting you see your food.
The clever part is the size of those holes. They’re far too small for microwaves to pass through, so the energy stays contained inside. Light, however, can get through—which is why you can stand there watching your soup rotate without the door needing to be one solid piece of metal.
In other words, the dots aren’t really dots at all. They’re the little windows in a safety screen, and without them, keeping an eye on your favorite frozen dinner as it cooks would be considerably more difficult.
How does a microwave keep radiation from escaping?
The dotted screen isn’t responsible for keeping microwaves contained all by itself. The interior is lined with metal, which keeps the microwave energy bouncing around where it can actually heat your food. The door is designed to seal that enclosure.
There are safeguards built in, too. Microwaves have safety switches that stop them from producing microwave energy when the door is opened—which is why opening the door instantly stops whatever is cooking, even if there’s still time left on the clock.
For a microwave that’s in good working order, there’s no reason to worry that those little holes are letting anything dangerous out along with the light. The FDA regulates how much microwave energy an appliance is allowed to give out, and the permitted amount is well below harmful levels.
