- For other uses, see Poison ivy (disambiguation).
Poison-ivy (Toxicodendron radicans or Rhus toxicodendron), in the family Anacardiaceae, is a woody vine that is well-known for its ability to produce urushiol, a skin irritant which for most people will cause an agonizing, itching rash.
Habitat and range
Poison-ivy grows vigorously throughout much of North America, but particularly in the American Midwest. It can grow as a shrub up to about 1.2 m (4 ft) tall, as a groundcover 10-25 cm (4-10 in) high, or as a climbing vine on any and every support. Older vines on substantial supports send out lateral branches that may at first be mistaken for tree limbs.
Poison-ivy is apparently far more common now than when the Europeans first entered North America because it has profited immensely from the "edge effect", enabling it to form lush colonies in such places.
How to recognize poison-ivy
The leaves are compound with three almond-shaped leaflets, giving rise to the doggerel, "Leaflets three, let it be". The berries (actually drupes) are a grayish-white color and are a favorite winter food of some birds.
Poison-ivy looks somewhat like ivy. The color ranges from light green (usually the younger leaves) to dark green (mature leaves), and bright red in fall. The leaflets are 3-12 cm long, rarely up to 30 cm. Each leaflet has a few or no teeth along its edge, and the leaf surface is smooth. To compare, blackberry and raspberry leaves also come in threes, but they have many teeth along the leaf edge, and the top surface of their leaves are very wrinkled where the veins are. The stem and vine are smooth, brown and woody, while blackberry stems are green with thorns.
Virginia creeper (Parthenocissus quinquefolia) vine can look like poison-ivy. The younger leaves can come in groups of three but have a few more serrations along the leaf edge, and the leaf surface is somewhat wrinkled. Virginia creeper and poison-ivy very often grow together, even on the same tree.
Western Poison-oak leaves also come in threes on the end of a stem, but each leaf is shaped somewhat like an oak leaf. Western Poison-oak only grows in the western United States, although many people will refer to poison-ivy as poison-oak. This is because poison-ivy will grow in either the ivy-like form or the brushy oak-like form depending on the moisture and brightness of its environment. The ivy form likes shady areas with only a little sun, and tends to climb the trunks of trees, and can spread rapidly along the ground.
Beware of dead poison-ivy: it still has plenty of urushiol, and will give the same effect. Compare the thick vines of grape, with no rootlets visible, to the vines of poison-ivy, with so many rootlets that the stem going up a tree looks furry.
Effects
The skin rash, featuring fluid-filled blisters and reddened areas that itch intensely, is caused by an irritating oil, urushiol. Urushiol binds to skin cell membranes, changing their configuration, so that the body's immune system no longer recognizes these cells as belonging to the body and attacks them as foreign. Some people are susceptible to the rash, and others aren't, but reactions can change during a person's lifetime. Someone who was formerly not subject to it may become very sensitive, and vice versa.
Normally, it takes about twenty-four hours for the rash to first appear, though it may worsen during the next few days and may appear to spread, when in fact what is happening is that areas that received a lesser dose are latently reacting. The rash takes one to two weeks to run its course, but normally does not leave scars. Severe cases will have small (1-2 mm) white fluid-filled blisters on the skin.
Treatment
When a person has been in contact with poison-ivy, there are several measures that may be taken to prevent or lessen a rash. Zanfel and Tecnu are commercial preparations designed to 'unlock' urishiol from the skin. If applied within 20 minutes of exposure to poison-ivy, these may be effective in completely preventing an outbreak. Zanfel, the more expensive of the two by far, may be effective at any stage of a poison-ivy outbreak.
Once an outbreak has occurred, cold compresses, calamine lotion, and hydrocortisone ointment are commonly used to abate the symptoms. Most poison-ivy rashes will self-resolve within 14 days without treatment. If the rash is severe or if it does not resolve within 14 days, a doctor should be consulted.
One traditional remedy is to find plants of jewelweed (Impatiens species), and to take the whole plant, crush it into a ball, and vigorously rub it into the exposed area. Or, crush some jewelweed stems in a container, and use a cotton ball to soak up the juice. Spread it on the rash as soon as possible.
Another method is to take mud, preferably clay mud, and vigorously rub it in. Affected people can also use either laundry detergents or strong soap to scrub the area before the rash appears.
Other home remedies, mostly ineffective, include acorn tea, banana peels (rub the inside of the peel on the affected area), birch tea, bulrush, burdock, cattail, chicory, comfrey, hemlock, milkweed, mint, spicebush , sumac (non-poison), sweet fern, thistle tea, and yucca.
Urishiol is an oil and is not washed off by plain water. People have had success in lessening the rash by wiping the area clean with alcohol, or mild soap, in order to break down the oil. Laundry detergent or Fels-Naphtha soap are more effective, though vigorous rubbing is necessary. Note that the application of any such chemicals to the skin might produce its own adverse reaction.
Prevention
Preventing exposure to poison-ivy involves ways of preventing the oil from getting on the skin.
- Wear long clothing, avoid any plants that look like poison-ivy.
- If you must wear short clothing, put thick lotion on areas that may be exposed to poison-ivy, like the legs. A suntan oil may work even better.
- If you handle tools that have touched it, wear gloves, then wipe the tools with alcohol immediately after using them, or throw them away.
Killing poison-ivy
Poison-ivy should never be burned, as the smoke particles carry the irritant and allow it to be inhaled; people that are extremely sensitive to poison-ivy could die.
Poison-ivy is extremely hardy and very resistant to herbicides. Some herbicides will not destroy the roots, allowing the plant to grow back the following year. Roundup and other grass killers do not affect poison-ivy. Some people recommend using a brush killer.
Another option is to physically pull up all the vines and roots but you must wear gloves and pants and a long sleeve shirt. Wrap the plants in a good garbage bag and bury them or dispose of them in a landfill.
Note on name hyphenation
The hyphenated form "Poison-ivy" is used, rather than "Poison Ivy" to clearly indicate that it is not a variety of ivy, just as "Poison-oak" is not a variety of oak.
External links
Last updated: 05-16-2005 05:55:54
