Rejection is usually caused by pressure of the jewellery against the skin that has been pierced, often caused by using straight bars on the body-surface or curved areas (such as the wrist, face or nape), or simply the body refusing to accept the piercing. Rings can get knocked around and that irritation can also cause rejection. Infection and allergy/sensitivity are also types of irritation and can lead to rejection. Some piercings may "migrate" to a more comfortable setting without being rejected. Eyebrows that are pierced too deeply will often migrate to a more comfortable position and stop. This is common with Guiches, Frenums, Brows and even Navels.
The signs of rejection include red, tender and raw skin at the opening holes of the piercing. The holes begin to get closer together leaving a thin scar as the dead skin cells are removed. This can happen extremely quickly or over a long period of time. It can also happen to a brand new piercing or one that has been healed for years.