Ear piercing itself isn’t dangerous, but if the pierced site isn’t kept clean than infection may set in. Signs to look for include redness, swelling, soreness or pus at the site.
With mild infections, sometimes the earring can be left in and treated by cleaning the area well and applying a topical antibiotic. In more severe cases, the earring will need to be removed and oral antibiotics will be prescribed. In such cases, after the infection clears and the hole closes, the ear lobe can be repierced. In some of the worst cases I have seen, the infection is so bad that the earring back is swallowed up the swollen, infected earlobe. This can be challenging to remove and treat for both the doctor and the patient.