The "black henna" used in temporary tattoos popular in Bali has tested positive for high concentrations of an allergen known to cause severe dermatitis.
Testing at WA's ChemCentre residues laboratory of a sample collected on the holiday island by The West Australian last month confirmed a 17 per cent concentration of p-Phenylenediamine.
The chemical is listed in the Australian poisons standard, the Standard for Uniform Scheduling of Medicines and Poisons, and banned for use in skin colouration products in Australia.
It is, however, allowed for use in hair dyes where concentrations are usually below 6 per cent, as long as the packaging contains appropriate warnings about the potential for skin reactions.
Scores of people, including some young children, have returned from Bali holidays with serious skin reactions requiring medical attention in recent years after getting a decorative temporary black henna tattoo.
Skin and Cancer Foundation dermatologist Rosemary Nixon, who specialises in contact dermatitis, said "black henna", was not henna at all. Henna, which caused few reactions, was a brownish colour.
She said on its own PPD was one of the strongest known allergens. However, some artists in Bali set their clients up for a double whammy.
"We have heard of and observed people mixing PPD with kerosene and by mixing PPD with a solvent it really facilitates it getting into the skin and leading to sensitisation," Associate Professor Nixon said.
One study found 80 per cent of people exposed to PPD became sensitised.
Not everyone would have a reaction immediately and some people could even have multiple tattoos before a reaction occurred.
But one reaction was enough to set a person up for a lifelong allergy to hair dyes and in some cases, dyes in clothing.
Ernest Tan, a fellow of the Australasian College of Dermatologists, echoed the warnings on the Federal Government's website smartraveller.gov.au, urging tourists to avoid the tattoos.
He said they would contain PPD.
"The darker it is, the more PPD it contains," he said.
Carrying out a skin patch test - as many of the Bali artists urge for anyone who raises concerns - was unlikely to help because reactions could take days or even weeks to become apparent.