The implants now at the centre of a worldwide health scare came from the now-defunct French company Poly Implant Prothese (PIP) and appear to have an abnormally high rupture rate. That risk, though typically low, is present in all implants.

Breast implants have been on the market since the early 1960s, after the first implants were developed by two plastic surgeons in Texas working with the silicone specialist firm Dow Corning Corporation.

The first woman to have silicone breast implants was in 1962 in the United States. Since then, between 5 and 10 million women worldwide, including an estimated 1.5 million to 2.5 million in the United States, have had breast implant surgery.

Although silicone implants are considered the more natural-looking option because they are more likely to appear and feel like real breasts, safety concerns have dogged them for years.

SILICONE OR SALINE

In 1992, the U.S. drugs regulator, the Food and Drugs Administration (FDA), decided silicone implants should be taken off the domestic market because their safety had not been fully established.

But U.S. silicone implant sales resumed in 2006 after the FDA approved implants sold by Allergan and Johnson & Johnson's Mentor unit on condition that the companies would follow a sample of 40,000 women for 10 years to look at safety issues.

In Britain, breast enlargement is the most common cosmetic surgery performed on women, the Medicines and Healthcare products Regulatory Agency (MHRA) said.

The operation is also hugely popular in Latin America. In Brazil, some 200,000 to 300,000 breast implant operations are carried out each year, according to the Brazilian Plastic Surgery Society.

Several types of implant are available, including those constructed from natural tissue taken from elsewhere on the body. This type of surgery is more usual in breast cancer patients undergoing breast reconstruction after a mastectomy.

More common implants used in cosmetic surgery are silicone- or saline-filled devices which are placed under the breast tissue to boost size and enhance shape.

The implants are usually inserted via an incision under the breast, but can also be put in using a cut in the armpit or around the nipple. The operation is generally done under general anesthetic and takes up to one-and-a-half hours.

NO LIFETIME GUARANTEE

Experts warn, however, that breast implants are likely to need long-term care.

"Breast implants do not last a lifetime, they will need replacing at some point in the future," the British Implant Information Society says on its website.

It says modern devices are likely to last between 20 to 25 years, about 10 years longer on average than the older types developed in the early 1960s and 1970s.

In some countries where implants are popular among very young women - in Venezuela it is not unusual for parents to give breast implant surgery to teenage daughters as gifts - this could mean a woman going back once and possibly twice in a lifetime for more breast surgery.

Doctors say pain is frequent after surgery, and most clinics advise patients not to raise their arms above their heads for several weeks after the operation.

The MHRA lists other potential problems, such as the risks of infection, leakage or bleeding, possible creasing and kinking of the breast tissue, and temporary loss of sensation.

U.S. regulators warned this year that most women with implants were likely to need additional surgery within 10 years to address complications such as rupturing and leakage, two of the main problems associated with the PIP devices.

All this suggests the costs of breast enhancement surgery are likely to add up over the years.

According to one U.S. cosmetic surgery price guide, breast implant surgery with either silicone or saline implants can cost between $5,000 and $8,000, similar to costs in Britain.

So-called "revision" breast surgery is often more expensive, lengthier and more complicated than the first time around because of existing scar tissue and the need to remove or adjust the original implants.

Anyone offering significantly lower priced surgery may be cutting corners on aftercare or follow-up consultations, experts say, and patients should beware.

($1 = 0.6394 British pounds)

(Editing by Alessandra Rizzo)

• A Permanent Economic Emergency