An investigation has been launched into the fashion trend of henna tattooing after allegations that artists could be using potentially harmful dyes.

Oxfordshire's trading standards officers are concerned that some tattoo artists could be using a cheap black hair dye instead of genuine henna.

The dye contains Para-Phenylenediame Diamine (PPD), a toxic black chemical, which can cause skin blisters and lesions and can scar skin for life.

A hand being given a henna tattoo, a practice being probed by Oxfordshire trading standards officers. Picture posed by model Oxfordshire's principal trading standards officer, Kath Veal, said: "We have had a number of queries . The allegation is that some of the traders in the city centre are using hair dye with potentially damaging chemicals."

Henna tattoos have become increasingly popular, especially among children. Artists often set up stalls in Oxford's pedestrianised Cornmarket Street selling the temporary skin designs, which cost as little as £5 and take just minutes to complete.

Traditional henna is a harmless plant paste that naturally stains the skin rust-brown or red-brown, and has been used safely in India, the Middle East and north Africa for 9,000 years. PPD is faster to mix and apply, but can cause irreversible damage to skin, including pustules, blisters, oozing sores, intense itching, and scarring.

There is particular concern for pregnant women as PPD has mutagenic properties which can cause birth defects. Sean Phillips, 31, of Abingdon, an henna tattoo artist who practises on Cornmarket Street, said he uses natural ingredients. He was so concerned about rogue traders visiting Oxford from London that he contacted trading standards.

Henna -- the facts *Henna does not naturally dye skin black. "Black henna", has had substances added to it to make it turn black

*PPD (P-Phenylenediamine) is frequently added to henna to stain it black

*PPD stains the skin black within two hours and the stain lasts at least two weeks

*PPD is sold over the counter as a hair dye such as Bigen No. 59 Oriental black hair dye

*PPD is extremely dangerous because it is a toxin, capable of entering the bloodstream

*Once in the system, PPD toxins collect in the liver, causing liver and kidney damage, or asthma

*Henna only stains the outermost skin cells and fades in a few days to a week.