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No one wants to be stuck in the airport, as long lines, delayed flights, and frustrated passengers can make even the shortest trip feel much longer. Despite security tech projects that could change airport screening, the process can be even more of a hassle if you have SSSS on your boarding pass. This code means that you could be subject to enhanced screening that may involve the swabbing of your personal belongings, including electronics.

SSSS stands for Secondary Security Screening Selection, and it’s a Department of Homeland Security (DHS) designation. It’s used to identify passengers who need additional screening by the TSA. Passengers labeled SSSS typically don’t know the reason why, and neither do the TSA agents in charge of the screening. Often, it’s due to random selection, though the TSA can choose passengers for additional screening at its discretion. The DHS could also be selecting passengers using the Secure Flight program, which identifies suspected terrorists or other suspicious individuals.

Neither the DHS nor the TSA has publicly confirmed that the SSSS designation and the accompanying electronics swab are linked to Explosive Trace Detection (ETD). However, ETD screening is being carried out in some airports. It involves swabbing a passenger’s hands or belongings at the TSA checkpoint. The swab is then analyzed by a special device that can detect even the tiniest amounts of trace residue.

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Air travelers can be repeatedly selected for enhanced screening by the Department of Homeland Security (DHS) because their identification is similar to someone on a government watchlist. Because of this, the DHS developed the TRIP program, which generates a Redress Control Number (RCN) for affected travelers, which can be used when booking future flight reservations to avoid misidentification. However, having an RCN doesn’t mean that a passenger won’t get pulled for enhanced screening for other reasons.

In fact, anyone going through the airport can be subjected to further screening, as the TSA can pull you from the line when you’re going through a checkpoint. Even wearing baggy clothes could get you patted down, and your bags may be checked. The TSA doesn’t publicly disclose all its reasons for performing further screening, but it’s clear from what it has published online that it reserves the right to conduct such screenings whenever it feels necessary.

While it might be impossible to completely avoid such delays at the airport, TSA is expanding the precheck system to make the process smoother. You can also take some steps yourself that might help. First, empty your pockets and remove any big jewelry. Place your laptop in a bin before it goes through the scanner, make sure your devices are charged and ready to power on, and as you’re leaving the checkpoint, be sure to collect all of your items so you don’t have to backtrack later.