Truth behind airport 'drug swabs' that has left plane passengers stunned

Flying might be a wonder of the modern world, but getting through the airport is often a less than pleasant experience.

Whether it’s trying to stuff your cabin bag unceremoniously into one of those little boxes to make sure it’s the right size, or, of course, the security checks before you can sit and wait to anxiously board your flight - I mean we've all heard the horror stories of the x-ray scanners.

After placing your shoes in a box, handing over your toothpaste and shampoo, and being patted down, you may also have someone run a swab over your hand or bag.

You might assume that these are looking for drugs, but TikToker Caroline Steel, who presents CrowdScience on the BBC World Service explained that they are actually looking for tiny traces of explosives.

These can be lighter than one trillionth of a gram, and are what is left on someone’s hand or bag after they have handled certain materials which are most certainly not allowed on planes.

Caroline, who was recently stopped as a result of a false positive, explained in a video on her page that they detect the trace substances by putting them through a science machine called an ion mobility spectrometer.

"Inside the particles are heated, turning them into a gas, and then they're given a charge, which turns them into ions," she explained.

An ion is an atom or molecule that has an electrical charge, so it might have more protons than electrons, or vice versa.

"The ions then move through a tube which has an electric field across it," Caroline said.

Atoms have a lot of qualities such as their charge, their shape, or their mass which can affect how fast they travel, and Caroline explained that the ion mobility spectrometer analyses how fast particles pass through a tube.

This information is then cross-referenced with a 'database of known substances', and if an ion appears similar to a prohibited substance, then this sets off an alert.

While it's a brilliant device which can detect extremely small amounts of explosives even if someone has thoroughly washed their hands after handling them, Caroline said that it can also throw out a false positive sometimes as well, as she found out.

"Now as I have learned that doesn't necessarily mean you're carrying explosives," she said, "because sometimes harmless substances can look similar to explosive substances."

If this does happen to you, Caroline explained that you will be taken for further questioning to make sure that everything is alright before being allowed to continue on with your journey.

Many people took to the comments on her social media video to share their surprise at what the swabs are actually for.

"I actually always thought it was for drug testing, but explosives does make sense for an airport," wrote one.

Drugs are of course also a concern at airports, with measures like body scanners and sniffer dogs being used to detect illegal substances.

One person said their line of work had made them nervous, writing: "I work in a lab and i got swabbed at the airport. I was so afraid that it was going to detect some of the chemicals i had been working with the day before".

But another person wasn't so lucky and their job did see them questioned.

They wrote: "I used to work in film development and camera film contains a lot of nitrate. Despite explaining this to the people at Manchester Airport, I worked a shift the day before flying, I was interrogated for two hours about nitrate residue on my hands because of this swab.

"Obviously I then missed my flight."