Name: Umbolith.

AKA: Omphalolith.

Age: Can take many years to develop.

Appearance: Small, dark, firm to the touch.

What is it, some kind of fossil-like formation? Yes, exactly.

And where might I find one? In some ancient sedimentary outcrop along the coast? No, in your belly button.

Come again? Umboliths, or navel stones, are lodged deep within the darkest regions of your innie.

Who says? Dr Sermed Mezher, who recently posted a short video called Well I’m Gonna Go Clean My Bellybutton Right Now #hygiene.

And who is Mezher? He’s a YouTuber and medic who makes videos that are, generally, commentaries on other videos, in this case some footage of an umbolith extraction.

I feel faint. You’re not alone – a lot of people are triggered by the notion of umboliths.

What are they made of? Compacted dirt, dead skin, sebum, clothing fibres and other debris.

OK, now I think I’m going to be sick. And while they don’t normally cause problems, according to Mezher: “They can start to smell pretty bad.”

That’s it, here we go, hold my hair. What Mezher doesn’t mention is that umboliths are quite rare.

I wish you’d started with that information. According to WebMD: “Most people will never develop one.”

Why do we even have navels? The navel is the remaining scar after your umbilical cord is removed at birth. They come in different shapes – innies and outies – but only excessively deep belly buttons are prone to navel stones.

I don’t think mine is unusual, or at least I didn’t until this moment. In any case, WebMD says: “Being careful about cleaning your belly button will prevent navel stones.”

Well, I’m gonna go clean my bellybutton right now. A swipe with a cotton swab couldn’t hurt, but as long as you’re washing regularly, you should be fine.

OK, I’m feeling better now. Do umboliths ever present serious problems? Very occasionally, they can cause irritation, infection and an unpleasant discharge, which might necessitate surgical removal.

You’re setting me off again. Given how rare umboliths are, there are a surprising number of videos online of them being removed.

Interesting. Once I’ve seen the procedure, will I be able to unsee it? I’m afraid not.

In that case, I’ll give it a miss. I wish I had, to be honest.

Do say: “Less navel-gazing, more navel bathing.”

Don’t say: “Oh no – now I’ve dropped my tweezers in there.”