Diabetes as well as other haematopoietic abnormalities (Thrombocytopenia, neutropenia, and anaemia): All present difficulties for piercing, because they reduce the bodies ability to heal wounds properly. In the case of Diabetes, it has been well established that wound healing is impaired in people with Diabetes Mellitus. Diabetics may experience reduced collagen synthesis, impaired wound contraction (the closing up of the piercing hole), and delayed epidermal migration.
There is also an increased chance of infection in diabetics. This being combined with the bodies inability to close a wound effeciently creates a bigger risk. Furthermore, the mouth is a very filthy part of the human body where bactieria can thrive, so It'd be more risky than an ear piercing that is much easier to keep clean and bacteria free. After one gets their toungue pierced they are sent home with instructions on how to take care of the piercing. You need to frequently rinse your mouth with anti-septic mouthwash after every meal and for smokers after every ciggarette.
Before you have your toungue pierced, consult with your physician about it. As a matter of fact many piercing/tattoo parlors will not pierce a diabetic without written consent from a doctor.
