Many eczema-producing substances, such as ethereal oils, resins, balsams, organic acids and alkaloids, are of vegetable origin. It is well known that eczema may be caused by plants, even though the active substances have been isolated and chemically analyzed in only a few instances (Bloch's primin in Primula obconica) or demonstrated in some other way, as a rule by patch tests with substances known to be present (limonene and citric acid in lemon eczema and pinene and abietic acid in pine eczema). The active elements are most often leaves, petals and fruits, less frequently roots or bulbs, as a rule from annual herbaceous plants, wild and cultivated (flowers, vegetables and utility plants).
Among the ligneous plants (bushes and trees) particular attention has been paid to the wood and the bark. Many "exotic" trees are known to produce eczema through contact with the wood, but some trees that grow in a
GENNER V, BONNEVIE P. ECZEMATOUS ERUPTIONS PRODUCED BY LEAVES OF TREES AND BUSHES. Arch Derm Syphilol. 1938;37(4):583–589. doi:10.1001/archderm.1938.01480100036003