Hi. Generally if the piercing is done following strict precautions in a clean environment by a professional using sterilised needles and equipments chances of infection is less but if this things are not followed, bacterial infection can occur. Sometimes a person might be allergic to the material used in piercing, which might lead to allergic reaction. If its a pus contained swelling with redness.clean that area before that wash your hands and clean the area around the piercing with cotton swab or hot compress and dry the area with dry cloth twice daily.avoid using alcohol or hydrogen peroxide as it may cause irritation of that area. Kindly consult a dermatologist for further management.