Rates of allergy to hair dye have jumped in several countries as more and younger people colour their tresses, European researchers warn.

In an editorial in Saturday's British Medical Journal, dermatologists say case reports from Britain, Belgium, Portugal, Germany and Singapore suggest the incidence of the allergy is increasing.

Para-phenylenediamine, or PPD, and its chemical cousins called aromatic amines trigger the allergic reactions. Eczema may show up on the face or around the hairline, and in severe cases, a patient's face swells up leading to painful bruising that requires treatment in hospital.

More than two-thirds of hair dyes currently contain PPD or related chemicals, according to the article.

A recent survey in London found the frequency of positive reactions to PPD in patch tests doubled over six years to 7.1 per cent among adults with contact dermatitis, the dermatologists reported.

Fashionable locks

Market research suggests that the root of the problem is that dying hair is popular, especially among young people. The use of temporary tattoos containing high concentrations of PPD is also contributing, the paper's authors said.

In Japan, about 13 per cent of female high school students and six per cent of women in their 20s said they used dye in 1992. Among men in their 20s, two per cent dyed their locks.

By 2001, the proportions rose to 41 per cent, 85 per cent and 33 per cent respectively.

"Cultural and commercial pressures to dye hair and, perhaps, the widespread obsession with the 'culture of youth' are putting people at risk and increasing the burden on health services," the editorial concluded.

"It may not be easy to reverse these trends … as some patients have continued to use such dyes even when advised that they are allergic to them and risk severe reactions."

Allergic reactions to PPD in temporary tattoos may also lead to sensitivity to hair dye, sunblock and some types of black clothing.

Health Canada said PPD is an acceptable ingredient when used correctly, such as in products that do not come in contact with skin for a long period of time. Health Canada strongly advises a "patch test" for hair dye.

The Canadian regulator considers hair dye made with PPD to be safe, but it advises people to check if black henna is used in the ink of temporary tattoos.

Legislation in the European Union allows PPD to comprise up to six per cent of the ingredients in hair dyes for consumers, but there is no satisfactory or widely available alternative for permanent hair dyes, the editorial said.