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.
But the British Dental Association (BDA) says tongue piercing can cause infections, speech impediments, breathing problems and broken teeth.
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.