Most permanent hair dyes contain highly allergenic substances of the type phenylenediamines (e.g. p-phenylene diamine and toluene diamine). The leaflets of these products contain a description of how the consumer may perform a self test for hair dye allergy.
The test aims to identify the consumers who are allergic to hair dye and therefore should not color their hair.
The consumer is asked to place a small amount of hair dye on the skin ( e.g. behind the ear or in the elbow area) 24 -48 hours before the hair dye, and then observe whether there is an allergic reaction or not.
An international group of researchers have examined the knowledge about hair dye allergy self-test. This review is published as a scientific article. The researches also examined the leaflets of 20 different permanent hair dyes purchased in 7 different countries and from 13 different manufacturers.
The conclusion is:
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Hair dye allergy self test is not validated among consumers and we do not know whether it can correctly predict who will develop an allergic reaction to hair dyes.
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It is also not know whether the consumer can perform and interpret the test correctly.
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The instructions in the 20 surveyed hair color products varied widely, even if they were from the same producer.
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If you follow the instructions you will be exposed to large amounts of allergenic substances directly on the skin for a long time - most commonly 48 hours of exposure with an undiluted product - every time you color your hair.
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There is a risk of allergy caused by the test itself, as you can get allergies when exposed to allergens to even small areas of skin.
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Hair dye allergy self tests have yet not been proven to be safe for the consumer.
