The Surprising Reason Not to Spit Your Toothpaste Out

Pete Ross

Photo by National Cancer Institute on Unsplash

Like most of you, I was brought up to always spit my toothpaste out and then rinse my mouth with water. After all, the toothpaste tube says “DO NOT SWALLOW”, like it’s made of oven cleaner or something toxic that will shred your insides. There’s also the fact that while the minty taste is pleasant, you don’t really want a bunch of foam in your mouth either.

For the past couple of months though, I’ve been leaving my toothpaste in. I can’t even remember why to be honest, I think I read something somewhere that suggested you didn’t need to spit. So when I brushed my teeth at night, I figured I’d leave it in to maybe work its magic while I slept. I’d spit most of it out and just leave my teeth coated, then go to bed without giving it a second thought.

“Your teeth are whiter.”

That’s what my wife said to me a couple of days ago. Not a question, not a “hey, your teeth seem whiter.” Nope, straight out, like it was fact. I’d actually noticed it myself, but I figured it might have just been my brain tricking me. But there it was — a difference noticeable to both my wife and I that my teeth had gotten several shades whiter.

So for you, dear reader, I did some digging to find out why this is and whether you should try it. The great news is, there are benefits beyond just whitening.

Ingesting toothpaste won’t kill you

Look, there’s really no reason to swallow toothpaste, but ingesting a little bit because you’ve left it in? Harmless. The reason I know this is that I recently finished reading the incredible Chris Hadfield’s The Astronaut’s Guide to Life on Earth. Chris was one of the most experienced astronauts prior to his retirement, prior to which he spent 6 months on the International Space Station, where he had to brush twice a day. Astronauts can’t spit their toothpaste out for obvious reasons, so they swallow it.

My first thought was “do they use a specially designed toothpaste for astronauts?”

The answer is nope, while it’s made for the astronauts and is ingestible, it’s no different than regular ingestible toothpaste you can get at your drugstore. From his detailed account of life on the ISS, the astronauts are constantly conducting experiments — many of them on themselves. I’m sure the toothpaste thing has come up, and if it was an issue they would have invented something else. They haven’t.

Their toothpaste was called NASAdent though, which is kinda cool.

You’re giving the active ingredients time to work

The main ingredient, fluoride, needs time to get to work in strengthening your teeth. This is also true for any whitening agents present in the toothpaste. You need to brush for minutes (recommended time is 2 minutes) for this to occur, but the average brushing time for most people is 45 seconds. Then when you rinse out the toothpaste with water, you rinse out all the active ingredients along with it.

So leaving it in after brushing — even if you aren’t brushing for the recommended amount of time, means that the active ingredients have a long time to do their thing on your teeth.

There is literally no downside here, because keeping more fluoride in your mouth for longer can only be beneficial.

Do I need to do it every time I brush?

Probably not, but as with most things, consistency is best. I don’t leave toothpaste in when I brush after breakfast, because quite frankly I don’t want any foam left in my mouth at that point of the day. Before bed though? That’s a no brainer. You’re going straight to sleep which means no talking, drinking or eating and your mouth is shut, which gives the toothpaste the maximum time to be effective.

Now if you really want to whiten your teeth quickly then theoretically, brushing after each major meal and leaving the toothpaste in could have significantly faster effects. Realistically doing such would mean that your teeth are exposed to active ingredients for several hours of the day whilst at the same time neutralising all the factors that contribute to tooth decay, plaque and stained teeth.

How much do I need to leave in?

Going off my own experience, not a lot. It’s not like when you finish brushing you have to leave an entire mouthful of suds in there. You spit out the vast majority of it and if you want to (I do), you wash it off your tongue as well. That still leaves a thin layer all over your teeth that you don’t even notice. In fact, a couple of times I did a double take, thinking that I’d accidentally washed it all out whilst getting it off my tongue, so I touched my teeth with my fingers. Definitely still there.

Don’t expect too much though…

Look, if you have really stained teeth from coffee or cigarettes, or you want Instagram teeth so white that the light reflected from them could be seen in a black hole, you’re probably going to be disappointed. My teeth weren’t yellow or anything, but the last month or so of leaving toothpaste in has certainly improved them a few shades. Maybe in a number of months time my teeth will be really white, but we’ll wait and see.

Either way, I’m getting free tooth whitening because I’d have to brush my teeth either way. Try that before you buy one of those gadgets off Instagram or spend thousands on a dental treatment.

Oh, and if you’re using that nasty black charcoal toothpaste, maybe don’t leave that in…

One last thing

Everything I’ve talked about here has been related to your teeth getting whiter from leaving toothpaste in. An even better reason to leave it in though is because the fluoride will strengthen your teeth against decay, meaning fewer trips to the dentist and even better — fewer cavities that lead to fillings.


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I write about career, performance, psychology, self development and business humour. I'm an author, former national competitor in judo and strongman and a former military instructor.


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