Five patients who were exquisitely sensitive to Rhus antigen developed a generalized eczematous dermatitis after eating large amounts of "raw" cashew nuts. Three of four tested had positive patch test reactions to raw cashews and negative reactions to roasted cashews. A group of highly "Rhus-positive" healthy adult volunteers had positive patch test reactions to raw cashews, while "Rhus-negative" and slightly Rhus-positive volunteers had no reaction to raw cashews. No dermatitis could be produced by feeding large amounts of raw cashew nuts to two Rhus-negative volunteers.
The raw cashew nuts sold in organic food stores contain appreciable amounts of cashew nut shell oil on their surfaces. The oil is antigenically similar to Rhus oleoresin and causes a generalized eruption when ingested in large quantities by people highly sensitive to Rhus antigen.
Ratner JH, Spencer SK, Grainge JM. Cashew Nut DermatitisAn Example of Internal-External Contact-Type Hypersensitivity. Arch Dermatol. 1974;110(6):921-923. doi:10.1001/archderm.1974.01630120067016