TABLE OF CONTENTS Hair colouring has been practiced for many years and today millions of consumers use hair dyes. It is well known that ingredients of oxidative and direct hair dyes possess an allergenic potential. For example, p-phenylenediamine (PPD) and derivatives of PPD are contact allergens as evidenced by laboratory animal studies and human studies as well as clinical experience. In the following chapter we highlight some of the key studies relating hair dyes and their role in skin sensitisation and allergic contact dermatitis. Considerations such as skin penetration, metabolism, protein reactivity and the immune response are discussed. Finally, many of the animal and human studies available on hair dyes are reviewed, including diagnostic patch test studies, to help position the relationship between hair dye ingredients and skin allergy.
Allergic contact dermatitis (ACD) is the clinical manifestation or disease state resulting from skin sensitisation, a type IV, cell-mediated (delayed type) hypersensitivity response. The biological process of skin sensitisation occurs in two distinct phases. The first phase, called the induction or sensitisation phase, begins with the chemical hapten penetrating into the skin. A number of factors influence a chemical's ability to gain access into the viable epidermis, including molecular weight and lipophilicity ( i.e. lipid solubility). [1] The majority of known chemical contact allergens have a molecular weight below 500 dalton. [2] Once in the skin, the chemical hapten reacts with a carrier...
