Poison Plants

Contact Dermatitis

Saturday, February 27, 2010

Poison ivy grows over much of North America, from Canada to Mexico, especially in wooded areas although it can grow in a wide variety of soil types. The plants can grow as a shrub up to about 4 ft tall, as groundcover 4–10 inches high, or as a climbing vine on various supports. Poison ivy is more common now than when North America was first populated; real estate development adjacent to wild, undeveloped land has created "edge effects" enabling poison ivy to form large colonies. It is listed as a noxious weed in various U.S. states and Canadian provinces; poison ivy and its relatives are virtually unknown in Europe.

The deciduous leaves of poison ivy are trifoliate (“leaves of three, let them be”)with three almond-shaped leaflets. Leaf color ranges from light green (usually the younger leaves) to dark green (mature leaves), turning bright red in fall; sometimes, the leaves are reddish when expanding, turn green through maturity, then back to red, orange, or yellow in the fall. The leaflets of mature leaves are shiny and smooth and have few or no teeth along their edge.

Vines growing on the trunk of a tree become firmly attached through numerous aerial rootlets. These roots appear in abnormal or unusual positions and appear as reddish "hairs". Like leaves, these parts of the vine are extremely poisonous to humans. "Raggy rope, don't be a dope!" is a rhyme that warns tree climbers to be wary of trees have a furry or "raggy" appearance. During the winter, vines lose their leaves but the oil that causes a rash can be found in all parts of the plants, including the stems, flowers, and berries.

The rash caused by poison ivy is due to an oil called urushiol; this oil is a contact allergen that causes a delayed allergic reaction where immune cells migrate to the area of skin where contact occurred. Because the cells take hours to travel to this site, the rash does not show up immediately. When the oil gets on other surfaces, such as clothing, pet fur, sporting gear, or gardening tools, it can still cause a rash when that object touches a sensitive person’s skin. Urushiol does not affect everybody; around 15% to 30% of people have no allergic response, but most people will become sensitized with repeated or more concentrated exposure to urushiol. The oil looks like a milky sap that turns black after exposure to the air.

As mentioned above, the rash usually appears hours after contact with the urushiol, on average about 8-48 hours later but it can occur from 5 hours to 15 days after touching the plant. The rash usually takes more than a week to show up the first time you get urushiol on your skin but develops more quickly (within 1 to 2 days) with later contacts. The rash will continue to develop in new areas over several days but only on the parts of your skin that had contact with the urushiol or those parts where the urushiol was spread by additional exposure. The rash is not contagious; once the oil has been washed off, you cannot pass it on to another person or spread it to other parts of your body.

Symptoms of the rash include itchy skin where the plant touched the skin, red streaks or general redness where the plant brushed against the skin, small bumps or larger raised areas such as hives, and occasionally blisters filled with fluid that may leak out. The more urushiol that contacts the skin, the more severe the skin reaction. Sometimes severe reactions to very small amounts of urushiol are seen in highly sensitive people. Serious symptoms include swelling of the face, mouth, neck, genitals, or eyelids (which may prevent the eyes from opening) and widespread, large blisters that ooze large amounts of fluid. Without treatment, the rash usually lasts about 10 days to 3 weeks. In people who are very sensitive to urushiol, the rash may take up to 6 weeks to heal.

Most poison ivy rashes can be treated successfully at home. Initial treatment consists of washing the area with water immediately after contact with the plants. Wet compresses and cool baths can help relieve itching as can antihistamines and calamine lotion. Moderate to severe cases may require treatment by a physician who can prescribe corticosteroid pills, creams, ointments, or shots. The best way to prevent the rash is to learn to identify and avoid the plants. When you cannot avoid contact with the plants, heavy clothing (long pants, long-sleeved shirt, and vinyl gloves) and barrier creams or lotions may help protect you.

Urushiol is found in other plants that are in the same family as poison ivy. Related plants include poison oak, poison sumac, Burmese lacquer tree, the shell of the cashew nut, and the skin of mangoes. Sensitive patients should avoid these plants although mangoes can be consumed if the skin is removed and cashews can be eaten if shelled and roasted. Plants unrelated to poison ivy such as Gingko biloba may also have urushiol.

The American Academy of Dermatology estimates that up to 50 million cases of urushiol-induced dermatitis occur in the United States every year. As the weather turns warmer, we are likely to see our fair share of those here in Austin. Learn to recognize the plants and wear protective clothing. If you suspect contact with the plants, wash the skin immediately. As soon as you get home, remove your clothing and wash these in hot water. Make sure to also clean any tools or other objects that may have come into contact with urushiol. Remember that the oil can also get on pet’s fur and can expose you further. For continued problems, call our office for additional help.

J.Alex Martinez, M.D.

For more information, see:

Poison ivy.pdf

Now that winter is winding down and spring is upon us, it is tempting to spend more time outdoors and enjoy the comfortable temperatures. However, sensitive individuals have to watch out for poison ivy and plants like it that can cause very itchy and inflamed rashes. Read today’s blog to find out more about these plants and prevent itchy problems.