No Ill Nature: The Surprising History and Science of Poison Ivy and Its Relatives

A Japanese lacquer artisan working in 1948. Lacquer varnish protects the wood while giving it a silky sheen. (Associated Press)

A Japanese lacquer artisan working in 1948. Lacquer varnish protects the wood while giving it a silky sheen. (Associated Press)

André-Ignace-Joseph Dufresnoy, an army physician and medical professor from Valenciennes in northern France, became one of poison ivy’s most fervent supporters around 1780. Like many physician-botanists of the era, he collected unusual plants for his personal medicinal garden. He also gave botany lectures that were open to the general public. One day Dufresnoy showed some leaves of his “Rhus-Radicans” and spoke about its irritant effects. A young florist in the audience could not believe that such an innocent-looking plant could be so powerful. After the lecture he rubbed the leaves vigorously in his hands, egged on by one of Dufresnoy’s students. The florist soon regretted his impulsive act, but after the painful swelling and rash finally cleared, he came to tell the physician that an ugly old sore on his wrist had completely vanished.

Dufresnoy was thrilled with this apparent miracle cure and immediately began concocting medicines from poison ivy. To avoid causing rashes in his patients he boiled poison ivy leaves to make an infusion for internal use, first drinking it himself as a test. He reported that even a strong infusion made with 12 leaves produced only mild side effects: his stomach became slightly upset and his sweating and urination increased. He then prescribed the infusion, and later a distilled extract from his poison ivy plants, to people suffering a range of skin maladies and even to some with paralysis of the legs, claiming positive results in many cases.

During the French Revolution, Dufresnoy’s fondness for poison ivy nearly sent him to the guillotine. After sending some young plants from his garden to a physician friend, he wrote in 1794 to ask, “How are our dear Rhus? How I long to see them!” The letter was intercepted and Dufresnoy was arrested on suspicion of conspiring with the Russians (Russes in French), who were then threatening to join the wartime coalition against France. Fortunately, the political upheaval that ended the Reign of Terror also deposed the harsh judge who was about to hear his case, and Dufresnoy was able to explain to the authorities that “dear Rhus” referred to medicinal plants, not menacing foreign troops. After this lucky escape the doctor’s story has a poignant ending. Following his death in 1801 his skeptical pharmacist brother dug up and destroyed all the poison ivy plants in his garden. Dufresnoy would certainly have been saddened to see his lovingly tended Rhus plants ripped out like noxious weeds.

With a few exceptions, later physicians simply cited Dufresnoy’s work instead of building on it; most were reluctant to grapple with such a hazardous plant. Highly diluted solutions of poison ivy extract did find a place in homeopathy, a system of alternative medicine that flourished in the 19th century. Homeopaths and their followers believed that poison ivy could help relieve swollen glands, fever, and restlessness.

A Fine Coat

Dufresnoy’s dream of poison ivy as a panacea remained unfulfilled, but one of the plant’s relatives proved very useful—though not in a health context. Just like its American relatives, the Chinese lacquer or varnish tree (Toxicodendron vernicifluum) produces a sticky sap that can cause a virulent rash. Since prehistoric times the Chinese have collected and refined this sap to coat wooden and metal objects, and its use in Korea and Japan also goes back many centuries.

Though Europeans had their own plant-based varnishes made from such resin-rich trees as pines and balsams, they were impressed with the strength, resilience, and beauty of Asian lacquerware. In the 1880s German geographer Johannes Justus Rein, one of the first Westerners to study the lacquer-making process in detail, described how Japanese workers made parallel incisions on tree trunks and used shells to collect the sap, then carefully refined and aged the sap into multiple grades of lacquer for different uses. In the course of his research he contracted lacquer poisoning (urushi-kabure in Japanese) and described the symptoms:

It is a peculiar, not very painful, and not at all fatal, but always very disagreeable disease, always attacking one new to the work. . . . It appears in a mild reddening and swelling of the back of the hands, the face, eyelids, ears, the region of the navel and lower parts of the body, especially the scrotum. In all these parts great heat is felt and violent itching and burning, causing many sleepless nights. In two or three days the crisis is reached, and the swelling immediately subsides. In severe cases, small festering boils form also.

While exposure to raw sap and the purified liquid could cause lacquer poisoning, the varnish became harmless once it dried thoroughly. Lacquer coated everything from ordinary dishes to fine artistic creations embellished with pigments, gold, silver, and mother-of-pearl. Master craftsmen also built up thin layers of lacquer on wooden containers, and then carved it in elaborate floral and geometric patterns. Such decorative Chinese and Japanese lacquerware, exported in large quantities, became very popular in the West. During the 19th century Europeans even produced imitation lacquerware by “japanning” items with black varnish and gold paint, though such copies could not compare to the genuine articles.