A scientist has revealed the disgusting reason you should never use a hand-dryer in a public toilet and always opt for a paper towel instead.

An experiment by a scientist who goes by Devon Science on TikTok exposes just how much bacteria is lurking in the machines, which is sprayed all over freshly washed hands.

The video that has amassed 4.7 million views shows the scientist placing a petri dish underneath a dryer, and collecting the bacteria that it spurts out.

To make it a fair test she also collected bacteria from the atomosphere in her laboratory, and left both samples overnight.

The next day the petri dish with the hand-dryer germs showed a variety of different bacteria and fungus speckled across the plate — which appeared in white, yellow and black smudges.

However, the dish which was waved through the air — to mimic when someone shakes their hands dry —, remained completely clear.

She admitted this is why she avoids using hand-dryers and instead opts for using paper towels or shaking her hands dry.

For the next part of the experiment, Devon Science dabbed toilet paper — which she previously used to dry her hands with — on to a petri dish.

While this also grew a variety of bacteria it was far fewer than that from the hand-dryer.

Finally, she swabbed the inside vent of the dryer, which was so dirty the cotton bud came out black.

The results again showed a petri dish full of different kinds of bacteria, similar types to the bugs coming out of the blower.

Following the stomach-churning results Devon Science said: ‘Now I know where the bacteria are coming from, they are actually living inside the machine.’

While the laboratory scientist did not reveal which specific bacteria were captured, previous research shows that E. coli, hepatitis and bacteria found in feaces lurk in public restrooms.

Previous studies have also suggested hand dryers may fire bacteria onto people’s hands when they suck in the air around them — where the micro-organisms may be lingering.

One 2018 study, by researchers at the University of Connecticut and Quinnipiac University, tested if hot-air hand dryers in public restrooms were  sucking up bacteria from the air and dumping them on the newly washed hands.

The researchers exposed a petri dish to hot air from a bathroom hand dryer for 30 seconds.

They identified up to 254 colonies of bacteria sprouting inside the pot.

They then attached high-efficiency particulate air (HEPA) filters to the hand-dryers to stop the bacteria from the air passing through the dryer.

When they repeated the test they found the quantity of bacteria in the dishes had fallen by 75 per cent.

This suggested most of the bacteria being sprayed out of the hand-dryers came from the air in the public toilet.