People creeped out after learning why your pupils go red in photos

There's nothing worse than taking a group picture when you're all dolled up to the nines, only to realise it's been ruined by all of your eyes appearing demonically red.

Even if you edit it, you're then left with a gang of beady-eyed people staring back at you and it's just not Instagram worthy.

As well as it being the bane of many influencers lives, there is a pretty grim reason why your peepers suffer from the red eye effect when you are photographed with the flash on.

And some people are so disgusted by it that they've vowed to give up on their well-lit amateur photoshoots in favour of a shadowy shot - even though it's a good sign that your eyeballs are in good shape.

TikToker Nicholas Grant, who 'tests weird videography theories', shared a clip explaining the reasons behind the red eye effect which stunned a lot of social media users.

He explained: "You've probably heard that red eye in photos is caused by the flash reflecting back to the camera, but it turns out what actually happens is a little more interesting.

"If you're in a dark room, your pupil opens up really wide to let in the light and it's in this situation that you would use a flash. Normally, if your eye sees bright light, it closes up."

This is because the iris constricts the pupil to protect the retina and to help us process what we are seeing better.

Nicholas continued: "But a flash is too fast for the pupil to react.

"It's the pupil being open that causes the red eye. That's why some camera do a double flash - one to close the pupil and one to actually take the photo. But why do you get red eyes if your pupil doesn't close?"

Now this is the point where a lot of people wished they had scrolled past the content creator's video, as they reckon they were better off not knowing.

He added: "Well, it turns out that the colour you see is actually the flash lighting up the inside of your eyes and it gets the red look because of the blood vessels in your eyes."

So basically, it's not just an annoying camera glitch - the flash has the ability to take a look at what's going on behind the eyes, lights it up and immortalises it in your camera roll forever.

According to the American Academy of Ophthalmology: "A red reflex happens when the flash of a camera lights up the blood-rich retina.

"If the eyes are looking directly at the camera lens and the colour of the reflex in both eyes is red, that's usually a good sign that the retinas of both eyes are unobstructed and healthy."

Knowing that the back of their eyeballs were in good knick didn't cushion the blow for a lot of social media users though.

One said: "So that's literally us seeing the inside of our eyes?!" while another wrote: "That is a bit creepy ngl."

A third added: "So the eye hole is an actual f**king hole," as a fourth chimed in: "School could never teach this."

And a fifth commented: "That's scary asf!"

It certainly makes you look at snaps taken with a flash differently.