Generally, standard piercings like earrings won't set off the security scans. Even if they do, they're pretty simple to remove. However, certain metal body piercings may trigger the machines, requiring you to go through a manual pat-down.
A TSA agent may ask you to remove your body piercings in a private area if additional screening is necessary. Rather than taking the risk, remove any body piercings before you make it to the security screening.
If you are concerned about your piercings closing up, consider glass piercing retainers.

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