It's a detail that's been staring you in the face that you've probably never noticed.

Why do some public toilets have U-shaped lids?

Unlike our ones at home which go all the way around, seats in public stalls often have a space directly at the front of the seat and people are demanding answers.

Handy YouTube channel Bright Side revealed the answer for citizens of the US in a video that explained it was down to mandatory plumbing codes that made "open seats" mandatory in public bathrooms.

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But as news.com.au found out, things are a little different here in Australia.

"With one exception, there aren't requirements for U-shaped toilet seats to be used in Australia through the National Construction Code, the national 'standard' for plumbing," Master Plumbers chief executive officer Peter Daly told news.com.au.

"This exception is for what are known as 'adult change facilities' where a full-circle seat is required for those with special needs. There are also special requirements for making sure the seat can carry a higher weight and doesn't shift when users have limited mobility."

However, that doesn't stop you from seeing them in public spots around the country — and there's a reason.

"The U-shaped toilet seat is commonly found in public bathrooms because the gap in the front of the seat is also designed to be more hygienic for both males and females in a high-use environment," Mr Daly said.

"This keeps it as far away from the genital area as possible, which you would be less likely to need in your own home.

U-shaped toilet seat is commonly found in public bathrooms. Photo / Supplied via Youtube
U-shaped toilet seat is commonly found in public bathrooms. Photo / Supplied via Youtube

Yep, that's right — the gap is essentially to keep your private parts away from the seat as numerous people use it.

International Association of Plumbing and Mechanical Officials code development senior vice-president Lynne Simnick echoed this sentiment.

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She told The Sunthe design allowed "women to wipe the perineal area after using the toilet without contacting the seat".

Peter also said the U-shape was often installed for ease of use and maintenance, adding "a break in the front of the seat means that it needs to be thicker and stronger to be 'self-supporting' — another reason it's not as often found in the home".

Understandably, some have been grossed out by the revelation.

"This is why I rarely use public bathrooms unless absolutely necessary," one person wrote on social media, echoing the pretty much everyone's thoughts on the matter.

But hey, at least we know now.