Myth: Chewing gum sticks inside you

This week Kat's been getting her teeth into a sticky subject for her mythconception...

Kat:: Are you a fan of chewing gum? I love the stuff and get through several boxes of peppermint gum every week. But I'm always careful to dispose of it carefully in the bin, and never swallow it, because I've heard the stories that it can stay in your gut for up to seven years. It certainly persists on pavements, desks and pretty much everywhere else people without good gum etiquette care to stick it. Flagrantly disregarding this advice, Naked Scientist Georgia's sister apparently swallowed a meter-long stick of chewing gum when she was six. So was it still working its way through her system when she hit her teenage years?

Well, luckily for Georgia's sister - and presumably her panicked parents - this is a myth. So what's the real story?

As the name suggests, chewing gum is designed to resist being broken down by the normal processes by which we digest our food - the first one of these being chewing. Because it's made of a base containing stretchy polymers, resins and other non-digestible components, chewing gum doesn't break down no matter how hard we mash it in our mouths. So it's pretty sturdy stuff. It's also resistant to the strongly acidic conditions in the stomach, passing through into the intestines in the same state it came in.

But once it gets there, it continues on its journey back to the outside world in the same way as the rest of our food, although possibly a bit slower than might be expected. In fact, gastroenterologists say that although they can sometimes see evidence of gum in people's guts when they're having a look in there, there's nothing that looks like it's more than a week old. This isn't unexpected - it's exactly the same for other non-food objects that get accidentally swallowed, including small coins or plastic toys, and even false teeth that mistakenly go down a grown-up's guts. We do swallow undigestible objects from time to time, especially kids, and unless they're particularly big or magnetic or batteries, nature usually takes its course and they'll eventually come out the other end.

There are a couple of reasons that the myth around chewing gum's longevity in the gut has sprung up. For a start, it's clearly not food - it doesn't break down in our mouths like normal chow, so we think we shouldn't swallow it. Then there are some published case studies, like the children who swallowed chewing gum every day for several years, and ended up having to have a large toffee-like trails of the stuff surgically removed from their intestines. Even more concerningly, in some cases the gum had collected other solid swallowed objects, such as coins or sunflowers seeds, adding to the problem. So it's still much better to spit rather than swallow your gum, especially if you're a daily chewer.

However, there are a few things that are hard to swallow. Pairs of magnets can pinch bits of the intestines together, leading to major problems, and it's also very bad to swallow batteries. And there's also an indigestible substance that does hang around in the guts for a long time, and that's hair. People with a compulsion to pull out and eat their own hair can end up with Rapunzel syndrome - a large hairball, known as a bezoar, trapped in their intestine that needs to be surgically removed. So that's definitely not a good idea. But humans have chewed gum - or at least stretchy tree resin and other indigestible plant matter, or even tar - for thousands of years. And although it's not a good idea to swallow it day after day, the occasional accidental swallow won't leave you with an unwanted intestinal visitor for years on end.