This section is from the book "Materia Medica And Therapeutics - Vegetable Kingdom", by Charles D. F. Phillips. Also available from Amazon: Materia Medica And Therapeutics: Vegetable Kingdom.
The pericarp of the nut contains abundance of a thick and caustic oil, capable of blistering the skin, and which has been used as a caustic for warts, corns, ringworm, and obstinate ulcers. The vapor of the oil, while the nut is being roasted for eating, will often produce violent swelling and inflammation. (The oil referred to is called cardol vesicans to distinguish it from the cardol pruriens obtained from the anacardium orientale. Properly diluted with simple ointment, we have found it a useful stimulant in alopecia areata and in circumscribed patches of indolent chronic eczema.)
Oil of cashew has been much lauded as a remedy for leprosy. The discoverer, Dr. Beauperthuy, of Cumana, communicated his secret to Dr. Bakewell, at whose instigation Dr. Milroy was sent out to Cumana by the College of Physicians to examine into the value of the alleged remedy and the truth of the reports. The result is that, while admitting that the oil has a certain value in alleviating the disease, Dr. Milroy is of opinion that much of Dr. Beauperthuy's success is to be attributed to the employment of hygienic measures in connection with a liberal allowance of fresh meat.