Hair dyes are more and more widely used, given the demands of current fashion. The age at which contact dermatitis due to hair coloring products occurs is beginning to decrease. In cases with cutaneous sensitivity to paraphenylediamine (PPD), the role of pre-existing labile tattooing with black henna may be important. Several types of allergic dermatitis have been described. Allergic contact eczemas to PPD are the type most frequently noted. The clinical symptoms will differ between hairdressers and other patients. Some cases of eczema due to hair dyes applied to eyelids and eyebrows have been described. Immediate allergic reactions, going from localized to regional (rarely generalized) contact urticaria, are rather rare. Cases of allergic contact dermatitis with blanching of the skin and reports of rosette-shaped eruptions due to hair dyes have been reported rarely in beauty salon clients. A detailed cutaneous allergy workup will allow one to identify the etiology. Delayed skin tests (patch tests, semi-open tests, repeated open application tests) are useful in the investigation of contact eczema. Immediate skin tests (intradermal or prick) can be useful when in cases with contact urticaria or with other allergic conditions (e.g., rhinitis). In cases with sensitivity to PPD, the possibility of cutaneous cross reactivity must be considered. The diagnosis of allergic contact dermatitis to hair dyes will have occupational consequences for apprentice and experienced hairdressers. As for consumers, they will be seeking advice concerning their choice of substitute hair dyes.