Friend of The Food Geek, Crystal, asks,
"Why does celery make your tongue feel numb? I've always assumed that I wasn't washing it enough.. that it was the result of some pesticides or preservatives they spray on it... something that doesn't wash off easily, but a little bit of googling seems to say it's a chemical built into celery... was wondering if you had any take on it?"
Man, you think you know a vegetable, and you go and find some crazy stuff out about it. First of all, there are people who are allergic to celery. That's not the problem, but it's interesting to note. Unfortunately, nobody really knows why you get a numb tongue. I've checked through quite a bit of scientific literature, and most of it deals with the allergic reactions people have to celery.
There's a lot of talk about uses for celery in a holistic "medicine" sense, but I don't see anything like an anesthetic usage. There's a lot of talk about using it for helping with arthritis, hypertension, and urinary tract infections, but that doesn't translate into numbing either. Incidentally, I should mention that I will never give you medical advice, so don't stop taking your blood pressure medication and just eating celery instead because "The Food Geek told me to." That's just fuzzy thinking, and I'd hope you wouldn't engage in fuzzy thinking.
The closest anyone I've found has come to answering this question is probably what you found in your search: a post by Dr. Steve Mack, where he posted a link to a list of all of the chemicals found in celery. We'll come back to those. He also looked through them, and decided that the best chance of numbing would come from Eugenol, which is used in temporary dental filings numb the pain. He doesn't sound entirely confident with it, but it's what we have right now. I've heard from an unreliable source that the more green is in the celery, the more Eugenol, and thus the more numbing.
The thing about food is that even the simple stuff is pretty complex. We like to think that we can take a small part of food (Omega-3 fatty acids, calcium, Vitamin C, and so on) and expect that it's going to give us the benefit of eating the food itself, or that we can remove a small part of the food (fat, cholesterol, etc) and suddenly make it healthy.
Another interesting idea we have is that we can grow it to make it healthier or unhealthier. For example, if we grow all food with organic methods, then the food will be better than if we grow it with not inorganic methods, but synthetic ingredients, or perhaps more modern methods. This is a nice idea, but it's just not that simple. I'm not suggesting that we abandon organic or sustainable growth methods, but I am suggesting that not all farming methods originating in the past 100-200 years are inherently evil.
One of the ideas behind organic farming is that we don't want to use pesticides because, well, they're poisons. That's a great place to start, but if you take that statement as a self-evident reason to avoid non-organic food and stop your thinking there, then I believe you've done yourself a disservice. Let's look at part of that list of chemicals that everyday celery contains. Among its many components are arsenic and nicotine. Nicotine isn't a popular substance these days, and arsenic is famously known as a poison. Does this mean we should ban celery from being eaten, or at least we should regulate it so that children under 18 can't buy it?
Celery is a vegetable with many important properties, the most important of which being that it can amplify flavors of food that it's cooked in. It would be foolish to throw it out because you find some alarming substances in in its chemical list. That's like suggesting that, because a small percentage of the populace is sensitive to sodium that restaurants should be banned from using salt when they cook. What? They're trying to ban restaurants from using salt in New York? Sigh. (Though they say there may have been some miscommunication.)
Everything can kill you. Everything. If you drink too much water, it'll kill you. Water is one of the single most important substances to keeping us functioning normally, and if we drink too much, it'll kill us. Crazy, right?
Just because something is self-evidently true doesn't mean it's actually true. And any food advice that can be narrowed down to "this single substance will kill you," or, "if you want to live longer, then take this substance which has been found in foods that are good for you," is either an oversimplification or completely wrong. Maybe one day we'll completely understand how food works, but that day is not today.
So, to sum up: Your numb tongue may be because of Eugenol. More study needs to be done. But it's not because you didn't wash it well enough, and it's not an allergic reaction. I hope that helps. Oh, and don't ban salt.