Those who dye their hair frequently manifest allergic contact dermatitis (ACD) from p-phenylenediamine (PPD)-containing hair dye. PPD is known to be the most frequent sensitizer in hair dye, but there has been no documentation of this sensitizer having a role in chronic dermatologic conditions. Our department experienced a case of a 62-year-old woman with lichen simplex chronicus (LSC), who complained of aggravation after hair dyeing and made such an association. We conducted a prospective and retrospective study to further evaluate the clinical associations between the two. In our prospective study, patch testing was performed in selected patients who regularly carried out hair dyeing and also had clinical manifestations of LSC. Also a retrospective examination was conducted in cases where patch testing had been performed with PPD in the past for suspected ACD and further selected cases with concurrent LSC and/or other neurodermatitis. 11 and 14 patients in our prospective and retrospective study, respectively, presented with both LSC and positive findings to PPD. 5 (45.5%) and 4 (28.6%) patients in our prospective and retrospective study showed clinical relevance from clinical improvement after stopping use and rechallenge. We report several cases of patients diagnosed as having LSC and/or prurigo nodularis who showed clinical improvement after discontinuing the use of hair dye. The suggestion can therefore be made that hair dye could be a possible aetiologic agent causing LSC in those using hair dyes.