The dirtiest item you carry with you while you’re traveling may not be what you think.

A controlled lab experiment commissioned by Japan Rail Pass provider JRPass found that one frequently handled travel essential contained significantly more bacteria than shoes, luggage or even cell phones do.

Researchers swabbed several common travel items, then incubated the samples to measure bacterial growth in colony-forming units (CFUs).

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The results showed that passports — far exceeding every other item tested — contained 436 CFUs. 

Checked baggage ranked second in the study with 97 CFUs, followed by shoes at 65, hand-held luggage at 56, phones at 45 — and coats at 15, according to the test.

Primrose Freestone, Ph.D., an associate professor of clinical microbiology at the University of Leicester and a microbiology advisor for BBC Radio Leicester, said frequent handling can increase bacterial buildup.

The human hand already carries normal bacteria — but when people touch things in crowded places like airports, they also pick up microbes left behind by numerous other travelers, Freestone noted. 

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“The greater the handling of a passport by different people’s hands, the more and greater the variety of bacteria, fungi and even viruses will be deposited onto the surface,” she said about the JRPass findings, as reported by Travel + Leisure and other outlets. 

Freestone said the findings should serve as a strong reminder for people to be mindful of hygiene while traveling.

Airports and public transportation hubs are high-contact environments. 

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Travelers frequently touch shared surfaces such as check-in kiosks, security bins, handrails and luggage handles.

Wipe down high-touch personal items such as passports, phones and luggage handles before and after trips, experts advise.

To reduce exposure, Freestone recommended that people wash their hands thoroughly whenever possible, or use an alcohol-based hand sanitizer after handling travel documents and other shared surfaces.

“Washing hands thoroughly with soap and water, or using an alcohol-based gel, is one of the simplest and most effective ways to reduce potential exposure,” Freestone said.

She also advised wiping down high-touch personal items, including passports, phones and luggage handles, before and after trips.

“Clothing naturally collects microbes from our skin and the environments we move through. Immediately changing out of airport outfits and washing them after travel can help prevent those microbes [from] being transferred onto furniture, bedding and household surfaces.”

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While bacteria are a normal part of everyday life, being aware of how easily they transfer from item to item during travel can help reduce unnecessary exposure, she also indicated. 

JRPass also said on Instagram about its study, “Moral of the story? Wash your hands. Wipe your passport. Maybe stop eating fries immediately after check-in.”

Other items called out by experts for attracting an undue amount of dirt and germs include the seatback pockets on airplanes, plus seat belts. 

Freestone also recently commented on another common item that attracts far more dirt and germs than people think. 

She said people should change their kitchen sponges on a daily basis. 

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“How often you clean your kitchen sponge depends on what you have been using the sponge for,” the expert told The Daily Mail.

“If [it’s] for something likely to be germ-ridden, such as dirty vegetables or raw meat or fish, then I dispose of these after a single use — as it is not easy to clean all microbes off a kitchen sponge.”