TONGUE piercing, made famous by the likes of Scary Spice Mel G and Princess Anne's daughter Zara Phillips, is a dangerous health hazard and should be avoided, dentists warned this week. The studs can become infected, causing blood poisoning, toxic shock syndrome or can interfere with breathing. Nerves and veins in the tongue can be damaged, say the British Dental Association. In addition, the studs can come loose and be inhaled or swallowed. In some cases they have been known to cause speech impediments.