An increase in people colouring their hair at a younger age has seen a "dramatic increase" in allergic reactions to hair dye, an allergy specialist says.

Itching of the scalp, redness and swelling of the face were symptoms, the latest issue of Allergy Today magazine says.

There had been a "dramatic increase in allergic reactions to hair dye internationally," said Dr Vincent St Aubyn Crump, of the Auckland Allergy Clinic.

In the past, hair dye was used to cover grey hair, but more people were now using it at a younger age, Dr Crump said. "Many people are also doing it themselves, and as the credit crunch worsens."

The main cause of the allergic reactions was a chemical in the dye called Para-phenylenediamine (PPD), the main colouring agent in permanent and semi-permanent hair dyes.

PPD was also found in henna tattoos, marketed at young people, and this was thought to be a major contributor to the increase in reactions, Dr Crump said.

PPD had caused serious problems in Germany, France and Sweden, but had not been banned in New Zealand.

New regulations meant that from July it would need to be disclosed on the label, including a warning of allergic reactions.

It was important to do a patch test, or allergy test, 48 hours before each hair dye to ensure there were no allergic reactions, Dr Crump said.

- NZPA