What are the causes of blood blisters under tragus piercings?

Irritation : Blood blisters most likely result from trauma or rubbing of the ornament on the skin. Infection is a concern if there is pain or swelling and the danger of piercing s close to or through cartilage of the ear is the risk of allowing skin bacteria to get into the cartilage which can produce difficult to treat infections and potential loss of normal cartilage resulting in ear deformities