Image copyright SPL

This image of a cyst growing on the back of the head is gross enough, but a video of one being burst?

I have to admit I'm responsible for some of the 36 million views of HUGE CYST EXTRACTION (capitals not mine).

It's a gruesome experience reminiscent of a never-ending tube of toothpaste or watching an ice-cream seller slowly fill a cone.

And it's not alone, there's the allure of Woman's 20-Year-Old Cyst Finally Gets Popped or the disgustingly named The Pus Cannon.

Dermatologist Dr Pimple Popper, whose real name is Sandra Lee, gleefully tells her million-plus subscribers: "I know you guys love them."

On the BBC World Service's Health Check programme, we subjected one innocent volunteer, Matt, to his first cyst-burst viewing.

"Oh gosh, she's using scissors to cut it off, it's gross, argh," he squealed, but he stuck with it. "Aw, look at that, it's amazing what's in there."

Disgust

So why do they have such an, albeit nauseating, appeal?

The answer is all down to "disgust", says Daniel Kelly, an associate professor in the department of philosophy at Purdue University and author of the book Yuck!.

Disgust is an emotional response that protects us from things that are poisonous or likely to spread infectious disease, whether it's rats or spoilt food.

Prof Kelly tells the BBC: "One of the really salient things that disgust keeps an eye out for are abnormal bodily fluids - so that is the key to these videos I think.

"What disgust does is when it detects one of these things, it keeps our attention trained on it, so it sort of generates this fascination."

And he argues such videos are a safe way to experience the "thrill" of disgust.

He says: "I think of it as analogous to the thrill people get riding a rollercoaster, or bungee jumping, where you get the 'voltage' of an emotional experience, without actually being at risk.

"Watching these kinds of videos, you get the thrill of an interesting emotional experience of feeling disgust, but you're not at risk of catching anything."

Dr Nisith Sheth, a consultant dermatologist for the British Skin Foundation, says: "I'm fascinated by the way people are really drawn in and people have become obsessed with them."

The growths - called epidermoid cysts - are sacs of dead skin cells and fats under the skin.

They are often found on the face, neck, chest, shoulders or near the genitals.

They are different to boils or abscesses, which are caused by an infection and filled with pus.

Dr Sheth, who treats people with them every day, says: "I'm used to seeing these things, they don't disgust me.

"One of the satisfying things is seeing it come out, and part of it is almost purging somebody of something which is foul or offensive.

"Often the people having it done on them don't want to watch, but I get frequent requests from partners and friends wanting to watch."

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