Ep 34: AVOID This Ingredient Before Going to the Airport!

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The One Ingredient You Should Never Use Before Going Through Airport Security

After a cross-country drive and a very chaotic travel schedule, I got a call from my mom who had just been stopped at airport security. Her hands were swabbed and she tested positive for a chemical used to make explosives, and she was understandably pretty rattled about the whole thing. To me, a cosmetic formulation chemist with extensive oral care experience this came as no surprise. I said “well yeah, you use sensodyne toothpaste”

So today we're talking about potassium nitrate, why it's in your toothpaste, why that's actually fine for your teeth, and why you should probably avoid using it before you go through TSA.

What potassium nitrate actually is

Potassium nitrate is a salt compound made up of two parts: a positively charged potassium ion and a negatively charged nitrate group. If the word "nitrate" is ringing a bell, it's probably because there was a big scare about nitrates in salted and processed meats. And yes, potassium nitrate is used to cure meats, but that's just one of many places this compound shows up in everyday life.

Nitrates are naturally occurring compounds made of nitrogen and oxygen, and they're found in soil where they play a critical role in plant growth. If you've ever fertilized a garden, there's a pretty good chance you were working with potassium nitrate, since it delivers potassium, nitrogen, and oxygen all at once, which is basically a full buffet for plant cells.

Each nitrate molecule is made up of one nitrogen atom bonded to three oxygen atoms, and when those molecules get excited (by heat, specifically), the oxygen atoms release very quickly. And if you know anything about fire, you know that oxygen is not exactly a calming influence. Nitrates are powerful oxidizers, which is the same property that makes them useful in fertilizers, meat preservation, and also gunpowder and fireworks. When heat is applied to a nitrate compound, it's essentially like cracking open a pressurized oxygen tank, and it combusts pretty soon after.

This is relevant to you as a traveler because Explosive Trace Detection testing (ETD, the swabbing you see at airport security) specifically screens for trace amounts of nitrates and other compounds associated with explosive residue. The equipment is sensitive enough to pick up very small quantities, and it doesn't really care where those nitrates came from before it flags you.

So why is it in toothpaste?

Making a claim that a product "reduces tooth sensitivity" is a drug claim under FDA rules, which means that to put those words on a label, a brand has to use an approved over-the-counter active ingredient. For sensitivity specifically, that active ingredient is potassium nitrate, which is why every sensitivity toothpaste on the market (Sensodyne, Colgate Sensitive, Arm & Hammer Sensitive, all of them) contains it. If the label says anything about sensitivity relief, the product has potassium nitrate; that's just how OTC drug regulation works.

The mechanism is that potassium ions are thought to accumulate at nerve roots in the teeth and block the pain signals that would normally fire in response to hot, cold, or sugary stimuli. So it's actually the potassium doing most of the work, not the nitrate part of the molecule. The nitrate is kind of just along for the ride.

Now, the evidence base for this is... interesting. One of the better studies we found compared a group using fluoride toothpaste plus a potassium nitrate mouthrinse to a group using fluoride toothpaste alone, and both groups saw significant reductions in sensitivity, but the mouthrinse group improved more. The obvious problem is that the control group wasn't using any mouthrinse at all, so it's pretty hard to know how much of that improvement came from the potassium nitrate versus the additional fluoride or just the mechanical action of rinsing. Tooth sensitivity is also pretty subjective as an outcome measure, which makes these studies tricky in general.

None of this means potassium nitrate doesn't help with sensitivity; it very well might, and there's a decent mechanism for why it would. But if you're weighing evidence, fluoride has a much better track record, so if you're not particularly prone to sensitivity, a regular fluoride toothpaste might be doing just as much for you.

What other products contain it?

After doing some digging, there are only a few products outside of oral care that use this ingredient: Estée Lauder's Set + Refresh Perfecting Makeup Mist, La Mer's The Treatment Lotion, and La Mer's The Hand Treatment. Those are the only non-oral-care cosmetic products we could find with potassium nitrate in the ingredient list, and it's worth noting that La Mer's hand treatment specifically could be relevant if you applied it before heading to security. The TSA agent who stopped my family member actually mentioned hand cream as a possible source, which is what sent me down this rabbit hole.

For oral care, if a product makes any claim about reducing sensitivity anywhere on the packaging, it contains potassium nitrate. No brand can legally make that claim without that ingredient.

What to actually do about it

If you're flying and you'd like to skip the extra screening experience (and make it to your gate on time), just use a regular fluoride toothpaste the morning of travel instead of your sensitivity formula, and leave the La Mer hand treatment for when you land. If you do get flagged anyway (it happens, because nitrates show up in a lot of places including food), it'll probably end with everything in your bag getting swabbed, which is annoying but not life-altering. ETD false positives from everyday products are more common than people realize, and TSA agents have seen it before.

Potassium nitrate is scary or that sensitivity toothpaste is dangerous, but chemistry doesn't really care about context, and the same compound that's soothing your nerve roots is also the compound that airport screening equipment is specifically designed to detect. The more you know!