Dear Science

Dear Science,

When I use a dirty microwave, do the stanky flavor fumes of other people’s encrusted foods infuse MY food? I know it SEEMS like they would, but do they? Actually? Either way, boo on dirty microwaves.

Stinky Chef

If you can smell something, it’s putting out chemicals into the air. If you can breathe in these old bits of food, your helpless meal in the microwave is going to suck them up, too. Almost certainly yes, food cooked in a dirty microwave is going to share with encrusted meals past.

It all comes down to what smells are: your brain’s way of interpreting all the chemicals we’re constantly bathed in. The insides of your nose and throat are packed with special kinds of chemical-
detecting cells called olfactory epithelium. The sense of smell is nothing other than these cells detecting chemicals floating through the air. To turn these chemicals into smells, the olfactory epithelium makes little chemical-detector proteins called odorant receptors; the human genome has at least four hundred of these little chemical amplifiers. A given smell is actually a combination of a handful, a dozen, or even hundreds of signals from these amplifiers. From four hundred amplifiers, through these combinations, we can detect a vast number of different odors. Our sense of smell is fast, reliable, incredibly sensitive, and specific at detecting almost anything we’re likely to encounter. (Most other mammals—dogs, cats, mice, and rats for example—have more like a thousand different chemical amplifiers encoded in their genomes, giving them an even broader and more discriminating sense of smell. About half of the odorant receptor genes in humans appear to have been broken during our evolution, leaving us with our relatively modest slate.)

Our sense of smell is really a sort of early detection and warning system. We can smell something in the air, generally, well before there is enough around to do us harm (a comforting thought to consider when taking your next trip on Metro). Funk is your friend, your way of not dying from eating a contaminated microwave burrito.

We still don’t really know how these hundreds of odorant receptors work. All that is certain is that they are ancient genes, inherited from the earliest of fish and vertebrate organisms. The complicated task of smelling is accomplished through some voodoo of quantum mechanics, at the scale of the universe where things rub against one another without really touching, where physics doesn’t work quite the same. The finest engineers—with the best chemistry and physics knowledge, nanoengineering, and circuit design techniques—cannot even come close to the magic of a rat digging through a pile of trash, smelling out an edible morsel.

Funkily Yours,

Science

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