Poison ivy (Toxicodendron radicans or formerly, but incorrectly Rhus toxicodendron or Rhus radicans) is a plant in the family Anacardiaceae. The name is sometimes spelled "Poison-ivy" to indicate with the hyphen that the plant is not a true Ivy or Hedera. It is a woody vine that is well known for its ability to produce urushiol, a skin irritant that causes an itching rash for most people, technically known as urushiol-induced contact dermatitis.
| Poison ivy | |
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| Species: | T. radicans
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| Toxicodendron radicans | |
Taxonomy
Poison ivy is subject to frequent taxonomic reclassification and confusion; it is currently divided into eastern and western species in the Toxicodendron genus. At least six distinct subspecies of Toxicodendron radicans are recognized. Complicating identification and taxonomy are the fact that the species (even a particular subspecies) can be highly variable in growth habit and leaf appearance.
Habitat and range
Found normally in wooded areas, especially along edge areas, poison ivy grows vigorously throughout much of North America, including all states except Alaska. It also grows in exposed rocky areas and in open fields and disturbed areas. The plants can grow as a shrub up to about 1.2 meters (4 ft) tall, as a groundcover 10-25 centimeters (4-10 in) high, or as a climbing vine on various supports. Older vines on substantial supports send out lateral branches that may at first be mistaken for tree limbs.
Poison ivy is more common now than when Europeans first entered North America. Real estate development adjacent to wild, undeveloped land has created "edge effects", enabling poison ivy to form vast, lush colonies in such places. It is listed as a noxious weed in the US states of Minnesota and Michigan.
Poison ivy (and oak) rarely grows at altitudes above 1500 meters (5,000 ft).
Effects on the body
The reaction caused by poison ivy, urushiol-induced contact dermatitis, is an allergic reaction. Some people simply do not have an allergy to urushiol. Around 15%[1] to 30%[2] of people are immune to the effects; however, sensitivity can develop over time with repeated exposure. For those who are affected by urushiol, it causes a very irritating rash. In extreme cases, corticosteroids can be needed to treat rashes and severe itching. The first symptom of contact is a severe itching of the skin that develops into reddish colored inflammation or non-colored bumps, and then blistering of the skin occurs. In severe cases, clear fluids ooze from open blistered sores. Once the urushiol poison has had contact with the skin, it is quickly bound to the skin. The poison can be washed off within a short time after contact, but once bound to the skin, it cannot be washed away.
The oozing fluids released by itching blisters do not spread the poison. The appearance of a spreading rash indicates that some areas received more of the poison and reacted sooner than other areas. The blisters and oozing result from blood vessels that develop gaps and leak fluid through the skin; if the skin is cooled, the vessels constrict and leak less. If poison ivy is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty. If poison ivy is eaten, the digestive tract and airways will be affected, in some cases causing death.
Urushiol oil can remain active for several years, so handling dead leaves or vines can cause a reaction. In addition oil transferred from the plant to other objects (such as pet fur) can cause the rash if it comes into contact with the skin.[3]
If a reaction occurs, eating mangos can magnify the allergic reaction and, for some, lead to the need for medical attention.[4]
Characteristic appearance
The leaves are compound with three almond-shaped leaflets. The berries (actually drupes) are a grayish-white color and are a favorite winter food of some birds. Hence the mnemonic,
"Leaves of three, let it be; berries white, danger in sight."
The color ranges from light green (usually the younger leaves) to dark green (mature leaves), turning 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. In comparison, blackberry and raspberry leaves also come in threes, but they have many teeth along the leaf edge, and the top surface of their leaves is very wrinkled where the veins are. The stem and vine of poison ivy are brown and woody, while blackberry stems are green with thorns.
Confusion with other plants
- Box elder (Acer negundo) saplings can look almost indistinguishable from poison ivy. While box elder trees often have five or seven leaflets, three leaflets are also common. The two can be differentiated by observing where the leaf stalk (the "branch" the three leaflets are attached to) meets the main branch. Another leaf stalk directly on the opposite side is characteristic of Box elder. If the three-leaflet leaves alternate along the main branch, it may be poison ivy.
- Virginia creeper (Parthenocissus quinquefolia) vines can look like poison ivy. The younger leaves can consist of three leaflets but have a few more serrations along the leaf edge, and the leaf surface is somewhat wrinkled. Most Virginia creeper leaves have five leaflets, however. Virginia creeper and poison ivy very often grow together, even on the same tree.
- Western Poison-oak leaflets also come in threes on the end of a stem, but each leaflet 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, tends to climb the trunks of trees, and can spread rapidly along the ground.
- Poison Sumac (Toxicodendron vernix) has compound leaves with 7–15 leaflets. Poison sumac never has only three leaflets.
- Blackberry vines bear a passing resemblance to poison ivy, with which may share territory. The chief difference between blackberry vines and poison ivy is that blackberry vines have spines on them, whereas poison ivy is smooth. Also, the three-leaflet pattern of blackberry vine leaves changes as the plant grows: the two bottom leaves both split into two leaves, for a total of five in a cluster.
- The thick vines of grape, with no rootlets visible, differ from the vines of poison ivy, which have so many rootlets that the stem going up a tree looks furry.
A young poison ivy plant
Use in homeopathy
Dilute forms of Rhus toxicodendrom are used in homeopathic medicine, most often as a remedy for musculoskeletal complaints with progressive stiffness that worsens with cold, wet, or inactivity and improves with motion, warmth, and use. The patient may have a red tip of the tongue or a red triangle on the tongue, herpetic outbreaks, and itchiness that improves with very hot water.[5]
There are numerous historical accounts of North American natives' use of the sap from R. toxicodendron to cure warts (see immunomodulators).[6]
Treatment
Applying cool compresses on the affected areas is sometimes adequate for relief. There are several over-the-counter lotions and ointments for treating poison ivy irritation and itchiness. However, in contrast to most allergies, diphenhydramine has no effect on the rash but can provide some relief from the itching. It is taken orally and not applied as a topical cream.[7] There are several prescription medications that are administered for treatment; for example, hydroxyzine hydrochloride (sold as Atarax or Rezine) helps relieve itching and dry blisters. In extreme cases cortisone and prednisone pills or shots are used.
According to the FDA, in case of known contact, exposed skin needs to be cleaned within 10 minutes of contact with rubbing alcohol, then washed with water only (soap can move the urushiol to other parts of the body). After washing the contact area the FDA recommends taking a shower with soap and warm water. When tools and clothing come into contact with the oil, the use of gloves can prevent contact between any oil and the skin. Tools and other objects that have had contact with the oil are cleaned with rubbing alcohol and water.[8]
Numerous folk remedies for poison ivy rash are known.[9]
See also
- Burow's solution, for treating poison ivy injuries
- Bentoquatam
References
- ^ [1]
- ^ [2]
- ^ http://www.aad.org/public/Publications/pamphlets/Poison_IvyOakSumac.htm
- ^ Mangos and Poison Ivy (New England Journal of Medicine Web Article)
- ^ Morrsion, MD, Roger (1993). Desktop guide to keynotes and comfirmatory symptoms. Grass Valley, CA: Hahnemann Clinic Publishing. pp. 323–327. ISBN 0-9635368-0-X.
- ^ Plants for a Future.
- ^ http://www.drgreene.org/body.cfm?id=21&action=detail&ref=559
- ^ http://pediatrics.about.com/cs/conditions/a/poison_ivy.htm
- ^ http://www.uspharmacist.com/index.asp?show=article&page=8_1996.htm
External links
- How Stuff Works: Poison ivy
- The Poison ivy tutorial
- Contact-Poisonous Plants of the World
- Treating Poison ivy, Poison-oak, or Poison Sumac
- Poison ivy myths
- Links to pictures (Hardin MD/Univ of Iowa)
- photos and stories
- Toxicodendron radicans images at bioimages.vanderbilt.edu
- Poison Oak at Wayne's Word
- Poison Ivy Information and Treatments