People with weak immune systems or underlying medical conditions are at increased risk of infection from fish pedicures, experts have warned.
Questions have been raised in recent months over people placing their feet in tanks of water containing dozens of tiny Garra Rufa fish, which nibble on dead skin.
While it carries a "very low" risk for healthy clients, those with conditions including diabetes and psoriasis have now been advised against the treatment.
The pedicures, which are popular in Asia, have been banned in some US states, including Florida, Texas, New Hampshire and Washington amid fears that infections could spread through open wounds.
The British Health Protection Agency today issued new guidance after a panel found fish tank water contained a number of micro-organisms and that infections could be transmitted either from fish to person (during the nibbling process), water to person (from the bacteria which can multiply in water), or person to person (via water, surrounding surfaces and the fish).
While it advised certain individuals to avoid treatment, it said any risk was "very low" for healthy clients when spas adhered to strict codes of cleanliness.
Dr Hilary Kirkbride, consultant epidemiologist at the British agency, said: "Provided that good standards of hygiene are followed by salons, members of the public are unlikely to get an infection from a fish spa pedicure, however the risk will be higher for certain people.
"This is why we feel it's important for salons to ensure the client has no underlying health conditions that could put them at risk, and that a thorough foot examination is performed to make sure there are no cuts, grazes or existing skin conditions that could spread infection."
Garra Rufa fish - a type of toothless carp - have become increasingly popular in salons, in part because of their novelty value.
Anyone considering a fish pedicure can help reduce health risks by ensuring cuts or infections on the feet or legs are given time to heal before treatment.
Clients are also urged to wait at least 24 hours after having a leg wax or shaving to minimise the chances of contracting an infection.
