BBC News' Toby Sealey reports from a body piercing centre

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.

If piercing equipment is not sterilised, there is also the risk of infections like HIV and hepatitis being passed on.

Allergy danger

The BBC's Jonathon Kent finds dentists' reservations not shared by customers at an Oxford body piercing shop

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.

Scary Spice - Mel G - is one of a growing number of people to have their tongues pierced

Other potential dangers include deep cyst formation, scarring, damage to veins and nerves and neuromas - overgrowths of nerve tissue.

Some orthodontists refuse to do any work on people with pierced tongues because of its effect on muscle position and the possible risk of encouraging speech impediments.

Dr Geoff Craig, chair of the BDA's health and science policy group, said: "People having tongue piercings are putting not just their oral health, but their general health at risk - and we strongly advise people not to."

But a spokesman said: "We have to live in the real world and realise people do have their tongues pierced.

"If they do, they should make sure it is done as cleanly and hygienically as possible."

Cleaning advice

The BDA says people should ask their dentists for advice on oral hygiene while the piercing is healing.

This includes advice on brushing to avoid inflaming the tongue and the need to use mouthwash to clean the bits of the mouth which the brush cannot reach.

Dr Craig said they should also ensure that their piercer sterilises equipment properly, using a device called an autoclave.

This costs at least �1,500 so the BDA says some piercers may not use it.

The association says anyone can carry out piercings, although those who operate premises should be licensed by local environmental health departments.

The European Professional Piercers' Association (EPPA) runs a voluntary register of about 450 piercers.

This monitors standards and trading in piercing and can be contacted on 0117 9603923.

The BDA says little research has been done into the cases where tongue piercing has gone wrong, but a member of the EPPA said she thought problems were not too widespread.

One case which was published in the British Dental Journal concerned a 25-year-old woman who was admitted to hospital after her tongue swelled up and she had difficulty swallowing.

She was found to be suffering from a rare condition called Ludwig's angina which did not respond to antibiotics.

The stud was surgically removed, but the woman later collapsed. She left hospital eight days later after further treatment.