[Interpretation and relevance of patch testing: false-positive and false-negative test reactions, compound allergy, cross-sensitivity].

This chapter reviews pitfalls and mistakes in patch testing. Most sources of false-positive and false-negative reactions are indicated and analysed. Cross-sensitivity among allergens is discussed and compound allergy is debated. Keys for establishing relevance are indicated, for a better reading and interpretation of patch testing by practitioners (trainees or experienced dermatologists).