Hair dye sensitivity testing: a critical commentary.

Although the large majority of users do not experience adverse skin reactions to hair dye products, a minority do. Most serious among these are allergic skin reactions, commonly to p-phenylenediamine and its derivatives. The consumer or hairdresser is expected (by the manufacturer) to limit the chance of expression of allergy by conducting a 'sensitivity test', which should provide the consumer with an alert for possible allergic reactivity. However, a self-conducted consumer test can only be useful if it meets a number of important criteria, including evidence that the test protocol works, that it can and is likely to be used successfully by the consumer or hairdresser, and that it does not present a significant health risk (e.g. an increased risk of developing allergy). In short, as with any in vivo test, the benefit must outweigh the risks. In formulating such a test, it should be determined in advance what are the acceptable levels of specificity (correct identification of negatives) and sensitivity (correct identification of positives). It is our view that any hair dye sensitivity test, whether supplied by the hair dye manufacturer or a third party, should be able to answer these questions.