C.I. Acid Orange 3 is a dinitrodiphenylamine derivative used exclusively as a dye (up to 0.2%) in semipermanent hair coloring products. This study was one of a series on semipermanent hair dyes, which included HC Blue No. 1 (NTP TR 271), HC Blue No. 2 (NTP TR 293), HC Red No. 3 (NTP TR 281), and