Introduction and Epidemiology

Contact dermatitis is the most frequent form (60%) of all the eczematous dermatoses and is among the most common diseases observed in dermatology and in occupational medicine. It is widespread in both occupational and non occupational settings: in the former case the incidence ranges from 85 to 98% of all job-related skin diseases; the peak prevalences are recorded in the building, leather, rubber, metallurgy, food, and chemical industries; health staff and apprentice hairdressers are also at high risk. From the aetiopathogenic and clinical standpoints, contact dermatitis can be subdivided into various types of reactions (irritant contact dermatitis, allergic contact dermatitis, photocontact dermatitis, noneczematous contact dermatitis, systemic contact dermatitis, and contact urticaria). Among these reactions, irritant contact dermatitis shows a more prevalent incidence today than contact allergy, for various reasons. The clinical differences among the various forms of contact dermatitis are due to a number of factors, especially the type of contact (exogenous, direct or airborne, and endogenous; the latter comes into action in subjects who have been prior sensitized by exogenous route, as occurs in case of systemic contact dermatitis), the chemical characteristics of particular causal agents, and the underlying pathogenic mechanisms in each case. A recent meta-analysis shows that one in five subjects from the general population suffers from contact allergy. The most common allergen is nickel, followed by fragrance mix, cobalt, balsam of Peru, chromium, paraphenylenediamine, isothiazolinones, and colophony. Various data demonstrate that seasonal factors can also affect the incidence of contact dermatitis.