Why do belly button piercings close up after a severe infection?

Belly button piercings are typically made from surgical steel, titanium, or gold. The trauma of an infection can cause some metals to be absorbed by the body, leaving behind a smaller hole than before. This process is known as extrusion and it is a normal reaction for many piercings when infected. Once healed, the hole may not completely close since there was trauma at that spot and the skin has already been broken but it will likely remain much smaller than before. In addition to metal absorption causing extrusion, severe infections can also cause scarring around the piercing itself resulting in tissue contraction which will make it even more difficult for your belly button piercing to stay open. It's important to keep your piercings clean and watch out for signs of infection like redness, swelling, tenderness and pain in order to prevent any long-term damage or potential closure of your belly button piercing.