Poison-oak is beautiful. In spring, its triple leaflets unfold with a delicate red tint. The smallest spring leaves are bronze. They enlarge as they open, to become a bright shiny green. At this stage, they really do resemble oak leaves, though the oak is not a relative. The green leaves yellow and then darken as summer’s warmth increases, until by fall a healthy plant is often an ombre blaze of scarlet with touches of green, brown, and gold. In winter, the plant drops its leaves, but the naked stems still contain a poison. That is the problem with poison-oak:
Urushiol
Urushiol is the substance that makes people who touch poison-oak itch. About 15 to 30% of people are not sensitive to urushiol at first, but with repeated contact, almost everyone develops a rash. About 25% of people who react have a strong reaction. Symptoms of contact include itching, blisters, inflammation, and sometimes burning and oozing. The rash begins about 24 hours after contact, and in severe cases should be treated by a doctor, particularly if the eyes are involved.
Urushiol is an oil that clings to everything it touches. Hikers may be extremely careful on the trail, yet still get a rash because they touch their clothes to launder them, or pet their contaminated dog. If the dog lies on the sofa before his bath, a hiker may get a rash that way.
The rash generally lasts one to two weeks, but may persist for a month or more. Since it is an allergic reaction, it often becomes stronger with repeated exposure. Urushiol works by changing the outer shape of skin cells, to a form that the immune system attacks as if they were invaders.
Prevention and Treatment
Stay on the trail. Boonie-crashers are much more likely to get poison-oak. Wear clothing that covers your arms and legs if you are in an area with poison-oak. Wear thick sun block. It makes an extra layer of protection against the oil. Learn to recognize the plant. Tecnu is a useful portable cleanser.
If you contact the plant, wash thoroughly. Plain water will not remove the oil, soap or detergent is necessary. This should be done as soon a possible after contacting the plant. In as little as 15 minutes, the oil bonds with the skin, making soap and water removal much less effective.
After the rash appears, some sufferers take antihistamines such as Benadryl to reduce the itch. Some believe in calamine. It may dry up any oozing, but will not calm an itch. Do not scratch, if possible, to avoid a secondary infection. Cooling the skin with ice packs or a fan may help.
In serious cases, a doctor will prescribe steroids. Healthy people who have a rash on 20% of their body should see a doctor. People in fragile health should see a doctor if the rash covers 10% of their body. If it is hard to breathe, or your eyes or tongue swell, see a doctor.
The Plant
Pacific poison-oak, Toxicodendron diversilobum, is found in western Canada, the western parts of California, Oregon, and Washington, and in Baja California. It is extremely abundant in oak woodlands and Douglas fir forests, appearing as a shrub in sunny areas, and as a climbing vine in shade. It prefers moist locations, but will grow on sunny slopes. The Latin “diversilobum” refers to the extreme variability of the poison-oaks leaves. They come in various colors and forms, from oak like to oval, and in colors from gold to red-violet.
Healthy, sheltered plants bear large shiny leaves, but plants in dry or windy areas have smaller, duller leaves, often speckled and of less distinct shape. Black speckles, also found on the stems, are dried sap, and contain urushiol. The leaves do come in three, usually, so the mnemonic “leaves three, let it be,” is a good one to teach children. Blackberry vines, among others, also bear heavily notched and lobed leaves in triplets, but blackberry stems look hairy.
The name of the plant is hyphenated to indicate that poison-oak is not an oak, although the leaves bear a superficial resemblance. It is a member of the Anacardiaceae family. Atlantic poison-oak, Toxicodendron pubescens, looks similar. It grows on the east coast and in the American south. Poison-ivy, Toxicodendron radicans, is a relative with almond shaped leaves, found mostly on the east coast. Cashew, mango, poison sumac, and pistachio are also Anacardiaceae. Gingko biloba carries urushiol too, though it is not a member of this family.
Conclusion
Poison-oak is a valuable member of the plant community. For one thing, it keeps hikers on the trail, and thus keeps erosion down. It provides food and shelter for wildlife, especially birds. After clear cutting or fire, poison oak is often one of the first plants to reappear, providing erosion control and shelter as the land begins to heal. Take another look at poison-oak. Just don’t touch.
