[Diagnosis of dermatitis due to plants].

Contact dermatitis from plants may occur by several mechanisms. It may arise as a result of simple irritation or by allergic mechanism; co-exposure to sunlight can evoke the phenomena of phototoxicity or photoallergy. Etiologic diagnosis require botanical, chemical and immunologic knowledges. Patch testing can be performed with pure allergens (primin, sesquiterpene lactones etc.), plant extracts (balsams, oleoresins etc.) or with the plant itself. The validity of patch test results is often difficult to determine: false positive reactions due to the presence of pesticides or herbicides, active sensitizations, cross-reactions.