The four 'dreaded' letters on airline boarding passes that travelers say they never want to see

Should you panic when you see "SSSS" printed on your boarding pass? Social media users are going viral for sharing their experiences after noticing the four letters upon arriving at the airport.

So, what does SSSS mean if it appears when you check in?

"SSSS are indeed four dreaded letters that no traveler should want to see on their boarding pass," Zach Griff, senior aviation writer for the New York-based travel blog The Point Guys, told Fox News Digital.

AIRLINE TRAVELER GOES VIRAL FOR MIXING COCKTAIL BEFORE BOARDING A PLANE: IS IT LEGAL?

"It stands for ‘secondary security screening selection,’ and it’s a measure implemented by security authorities in the U.S. to screen certain passengers with additional checks."

The Transportation Security Administration (TSA) will select passengers before the official flight departure.

"Selectees for this enhanced security are chosen in the days leading up to a flight when airlines share the manifest with U.S. security authorities," Griff added.

AIRLINE PASSENGER SAYS SHE RECEIVED 'CREEPIEST' TEXT FROM STRANGER WHO SAW PHONE NUMBER ON HER LUGGAGE TAG

Griff said that most people who receive SSSS before a flight will not be able to check in online, and will receive a printed ticket from an agent — this is exactly what happened to Jordyn Verzera and JT Mocarski, creators of the travel blog "The Mobile Homie.""

The travel-content-creating duo from Arizona have shared their experiences on TikTok each time they noticed the four S's on their boarding passes. 

Whenever they receive the SSSS on boarding passes and post it on social media, users flood them with questions in the comment section.

Verzera and Mocarski told Fox News Digital about what this additional screening process entails.

The first time Verzera and Mocarski encountered the four letters, only one of them was able to check in before their flight.

AIRLINE PASSENGER'S 'AWKWARD' SEATING ARRANGEMENT GOES VIRAL: 'NEVER GOING TO RECOVER'

Verzera attempted to get her boarding pass on the airline's app, but a notification popped up saying she had to check in with a gate agent, she said.

Verzera said she was confused until she spoke to an agent.

"They had to give me a printed boarding pass. He [Mocarski] could still use his digital one, and then I had to carry this pass around. It was marked and circled, and I had to show it like every step along the way," Verzera said.

"Instead of just going through one form of security … you had to get to the gate early, and they did an extra-deep screening when you departed. But where the big thing was, is, once we arrived, we actually ended up having to go through customs … and that was when the really deep search began."

AIRLINE PASSENGERS COULD BE REMOVED FROM FLIGHTS FOR GOING BAREFOOT: ETIQUETTE EXPERT WEIGHS IN

Verzera said that every item she packed had to be removed from her luggage, including her toiletry items. Those items were then laid out on a conveyor belt where everything was swabbed. Her laptop also had to be turned on in order to go through security.

"It was a little intimidating the first time around," she said.

Verzera had to arrive early at the airport to receive her boarding pass and had to wait in line for three hours. She said it took her another hour to go through the additional screening in customs.

Back in April, when Mocarski had gone through the SSSS process in Rome, it was significantly faster, he said. 

FLIGHT ATTENDANT GOES VIRAL ON TIKTOK FOR ATTEMPTING TO EASE COMMON FLYING FEAR

"It depends on which country … or which place where you're going, like the severity of the search, what it entails," Mocarski told Fox News Digital.

Griff agreed with Mocarski's point by adding that it depends on  the airport you are in, with some requiring an early arrival and a "complete paydown." Some airports may require a "personalized interview, along with more screening."

Mocarski thinks social media may have slightly villainized the extra security measure, he said.

"At the end of the day, it's random, like even the TSA agents, it's not like they're picking you. They know the remedies that they have to go through to make sure that they're doing the check," Mocarski said.

'AIRPORT TRAY AESTHETIC' GOES VIRAL AS SOME TRAVELERS HALT SECURITY CHECKPOINTS FOR PHOTO OPS

"It's just staying calm and just respecting their time. And they'll be back with you."

"At the end of the day … they're just doing your job," he added. "They're not there maliciously."

Griff said you might receive the SSSS for a variety of different reasons: "suspicious travel patterns like frequent one-way international trips, or many visits to high-risk countries," he said.

"SSSS can also be entirely random, and there’s no way to know when booking your flight whether you’ll be chosen as SSSS," Griff added.

For more Lifestyle articles, visit www.foxnews.com/lifestyle

Verzera said people might be concerned about "SSSS" as they feel the extra screening will lead to them missing their flight.

CLICK HERE TO SIGN UP FOR OUR LIFESTYLE NEWSLETTER

She and Mocarski recommend getting travel insurance for this purpose.

They also said that when "SSSS" appeared on their boarding passes, the plane "waited" and didn't leave any "SSSS passengers" behind.

"I think for us, and something we like to remind our friends of, is that travel isn't perfect," Verzera said.

"You grow the most when you're uncomfortable with travel – just understand that this happens. Just roll with it, and just let it be part of your day . . . go through it, and then [say], ‘I hope it never happens again.’"

Fox News Digital reached out to the TSA for comment.