The practice has become increasingly fashionable in recent years and has been made famous by stars like Scary Spice and the Princess Royal's daughter Zara Phillips. It says piercing always carries a risk of infection, but that risk is greater with mouth piercing because of the closeness of the airway.
Infection can cause the tongue to swell, blocking or restricting the airway.
In addition, bacteria under the tongue often spread quickly and can lead, in extreme cases, to the potentially fatal toxic shock syndrome or blood poisoning. If piercing equipment is not sterilised, there is also the risk of infections like HIV and hepatitis being passed on. The BDA says studs can come loose and can be swallowed or inhaled, leading to breathing problems. And accidentally biting a tongue stud can cause teeth to crack. There is also the possibility of a person developing an allergic reaction to a stud if it is not made from gold, titanium or surgical steel.