As poison ivy creeps up in the central and eastern U.S., poison oak is the bane of many an outdoor traveler or worker on the West Coast. Extremely common in some places, poison oak also comes in a diversity of growth forms, and its foliage easily blends in with brushy surroundings. Normally, the irritating allergic effect provoked by contact with poison oak in most people does not create permanent scars.
Poison oak, or Toxicodendron diversilobum, is a common shrub or vine on the West Coast, growing from British Columbia to Baja, California. Its common name stems from the soft-lobed leaves that bear strong superficial resemblance to the foliage of white oaks –- and suggests the affinity poison oak shows for these trees, often growing tangled along their trunks or in their shade. The plant is deciduous; the leaves turn a rich crimson-burgundy in autumn before falling.
Most people are allergic to an oleoresin that poison oak and other members of the Toxicodendron genus called urusiol possess. Merely brushing the stems or leaves of a poison oak plant can provoke its secretion. While symptoms vary, most people develop a rash -- frequently in linear flushes -- within several days. The inflammation is exceedingly itchy, and scratching can exacerbate the blistering typically accompanying the rash. Individuals with more severe allergies may experience pronounced swelling, enough to force shut eyes or puff up a face, or widespread blistering, in which case they should seek medical attention. The rash eventually subsides over a week or two.
In most cases, rashes caused by poison oak do not leave lingering marks like scars as the redness clears up as the allergic response concludes. However, if blisters or sores are not kept clean and become infected, more serious effects may result -- like abscessing and fever --, and in such cases, permanent scarring is possible.
Folk remedies for poison oak, poison ivy and the other Toxicodendron rogue’s gallery are legion, as are modern chemical products on the shelf. The main key to treatment is quickly -- immediately, if possible -- removing the offending urusiol oil. This may be done with cold water and gentle soap, or with specialized substances like Tecnu, an over-the-counter treatment. The effectiveness of washing decreases quickly over time, but still helps to restrict the spread of the oil. A good approach is to wash thoroughly any part of your body and anything else that may have been exposed to poison oak if you’ve been out in an area replete with the plants, even if you don’t see a rash.
To avoid poison oak, learn to recognize all its seasonal appearances: as a hard, rigid stalk during winter; bearing crimson leaves of spring or autumn growth; and in deep-summer glossy green. Recognize, too, its preferred habitat. In the Pacific Northwest, it tends to grow in drier, sun-sprayed lowlands, avoiding cool, dark mountain forests. In California, it is ubiquitous in many brushy hills, oak savannas and chaparral. Stick to trails where possible and, if working off-trail, avoid loose-fitting clothing and much dangling gear.
- Contact-Poisonous Plants of the World; Toxicodendron spp.; M. Rohde; 1998-2006
- "Wilderness and Environmental Medicine"; Toxicodendron Dermatitis: Poison Ivy, Oak, and Sumac; Aaron C. Gladman, MD; 2006
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