Allergic reactions to hair dye are increasing as more and younger people dye their hair, researchers said in this week's BMJ, formerly the British Medical Journal.

This can lead to dermatitis on the face and facial swelling, in severe cases.

More than two-thirds of hair dyes currently contain para-phenylenediamine, known as PPD. During the 20th century, allergic reactions to PPD became such a serious problem that it was banned from hair dyes in Germany, France and Sweden.

Current European Union legislation allows PPD to comprise up to 6 percent of hair dye, but no satisfactory or widely accepted alternatives to these agents are available.

Dermatologists reported that the frequency of positive reactions to PPD on patch testing is increasing. A study in London found a doubling in frequency over six years to 7.1 percent.

Market research also indicates that more people are dyeing their hair and are doing so at a younger age. A survey in 1992 by the Japan Soap and Detergent Association found 13 percent of female high school students, 6 percent of women in their 20s, and 2 percent of men in their 20s reported using hair coloring products.

By 2001 the proportions had increased in these three groups to 41 percent, 85 percent, and 33 percent, respectively.