[Incidence and significance of toxic and allergic contact dermatitis caused by machaerium scleroxylum Tul. (Pao ferro), a substitute wood for palisander (Dalbergia nigra All.)].

In recent years an increasing number of cases of primary irritant and allergic contact dermatitis has been observed after using the South-American timber Pao ferro (Machaerium scleroxylum). Since 1978 140 cases have come to our knowledge. The patients were mainly cabinet and furniture makers occupied in the sanding of veneer. Perioral dermatitis and cheilitis was also seen in persons playing the flute made of Pao ferro wood. Guinea pig sensitization experiments revealed a strong sensitizing capacity of the main wood constituent R-3,4-dimethoxydalbergione. Amounts of up to 2% were found in the heartwood. Mix-up of Brazilian rosewood (Dalbergia nigra) with its substitute (Machaerium scleroxylum) may occur accidently due to their similar appearance. However, a chemical differentiation is easily possible by determination of their constituents: while Pao ferro exclusively contains the strong sensitizer R-3,4-dimethoxydalbergione, the botanically related Brazilian rosewood (and also the East Indian rosewood--Dalbergia latifolia Roxb.) yields several other and weaker dalbergiones. In 41 of 55 patients tested epicutaneously with R-3,4-dimethoxydalbergione an acquired sensitivity could be demonstrated. The high amount of R-3,4-dimethoxydalbergione in Machaerium scleroxylum is primarily responsible for the outbreak of toxic dermatitis in veneer factories, half of which resulted in a sensitization. The risk of active sensitization is high if epicutaneous tests are carried out with the native wood dust. To avoid active sensitization it is better to test the pure constituent, if available, in a dilution of 0.1%.