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Poison ivy, sumac & oak.

Poison Plants: Ivy--Sumac--Oak

Those nasty weeds--poison ivy, poison oak and poison sumac* - grow practically everywhere in the United States, except Hawaii, Alaska and some desert areas of Nevada. They are the most common causes of allergic reactions in the United States and will affect ten to 50 million Americans every year.

* For the sake of convenience, "poison ivy" in this pamphlet refer not only to ivy but to sumac and oak as well.

Poison Ivy Rash

Poison ivy rash is really an allergic contact dermatitis caused by a substance called urushiol, (you-ROO-shee-ol), found in the sap ofpoison ivy, poison oak and poison sumac.

Urushiol is a colorless or slightly yellow oil that oozes from any cut, or crushed part of the plant, including the stem and the leaves.

You may develop a rash without ever coming into contact with poison ivy, because the urushiol is so easily spread. Sticky, and virtually invisible, it can be carried on the fur of animals, on garden tools, or sports equipment, or on any objects that have come into contact with a crushed or broken plant. After exposure to air, urushiol turns brownish-black, making it easier to spot. It can be neutralized to an inactive state by water.

Once it touches the skin, the urushiol begins to penetrate in a matter of minutes. In those who are sensitive, a reaction will appear in the form of a line or streak of rash (sometimes resembling insect bites) within 12-48 hours. Redness and swelling will be followed by blisters and severe itching. In a few days, the blisters become crusted and begin to scale. The rash will usually take about ten days to heal, sometimes leaving small spots, especially noticeable in dark skin.

The rash can affect almost any part of the body, especially areas where the skin is thin; the soles of the fact and palms of the hands are thicker and less susceptible.

Who's Sensitive, Who's Not

Sensitivity to poison ivy is not something we are born with. It develops only after several encounters with the plants, and sometimes over many years.

Studies have shown that approximately 85 percent of the population will develop an allergic reaction if exposed to poison ivy. This sensitivity, varies from person to person. Although that, are not sure why, scientists believe that an individual's sensitivity to poison changes with time and tends to decline with age.

The first bout of poison ivy, usually, occurs in children between the ages of 8 and 16, and can be quite severe. Ifthere is no repeated exposure to poison or urushiol, sensitivity will probably decrease by half by the time these individuals reach their thirties.

Investigators have found that people who reach adulthood without becoming sensitized have only a 50 percent chance of developing an allergy to poison ivy. Those who were once allergic may, lose their sensitivity later in life. However, dermatologists say you should not assume that you are one of the few people who are not sensitive-only 10 to 15 percent of the population is believed to be resistant. That same percentage (25-40 million people) is thought to be very susceptible to poison ivy. These people will develop a rash and extreme swelling on the face, arms and genitals. In such severe cases, treatment by a dermatologist will be required.

Recognizing Poison ivy

Identifying the plant is the first step toward avoiding poison ivy. The popular saying "leaves of three, let them be," is a good rule of thumb, but it's only partially correct. Poison oak or poison ivy will take on a different appearance depending on the environment. The leaves may vary from groups of three, to groups of five, seven, or even nine.

Poison oak is found in the West and Southwest, poison ivy usually grows east of the Rookies, and poison sumac cast ofthe Mississippi River. The plants grow near streams and lakes, and wherever there are warm, humid summers.

Poison ivy grows as a low shrub, vine or climbing vine. It has yellow-green flowers and white barries. Poison oak is a low shrub or small tree with clusters of yellow berries and the oak-like leaves. Poison sumac grows to a tall, rangy shrub producing 7-13 smoothedged leaves, and cream-colored berries. These weeds arc most dangerous in the spring and summer. That's when there is plenty of sap and urushiol content is high, and the plants are easily bruised. Although poison ivy is usually a summer complaint, cases are sometimes reported in winter, when the sticks may be used for firewood, and the vines for Christmas wreaths. The best way to avoid these toxic plants is to know what they look like in your area and where you work, and to learn to recognize them in all seasons.

What To Do About Poison ivy

Prevention is the best cure. The best way to avoid the misery of poison ivy is to be on the look-out for the plant whenever you are out-of-doors. what you are looking for, and stay away from it. The weeds can be destroyed with herbicides in your own back yard, but this is not a practical solution for forest preserves and other natural areas. If you are going to be in areas where you know poison oak or ivy is likely to grow, wear long pants and long sleeves, and, whenever possible, gloves and boots. Remember that the plant's virtually invisible, oily resin-urushiol-sticks to almost all surfaces, and can even be carried in the wind if it is burned in a fire. Studies have shown that a sensitive person may develop an internal inflammation from inhaling urushiol In addition, don't let pets run through wooded areas since urushiol may be carried home on their fur.

Barrier creams offer little hope against poison oak and ivy, although new products may offer some protection. These may soon be marketed throughout the United States. Dermatologists are also working on a skin treatment to prevent urushiol from penetrating the skin. Ask your physician about new treatments available that might help to protect you.

Treament--A Poison Ivy Primer

If you think you've had a brush with poison ivy, poison oak or poison sumac, follow this simple procedure:

* Wash all exposed areas with cold running water as soon as you can reach a stream, lake or garden hose. Ifyou can do this within five minutes, the water will neutralize or deactivate the urushiolin the plant's sap and keep it from spreading to other parts of the body. Soap is not necessary, and may even spread the oil.

* When you return home, wash all clothing outside, with a garden hose, before bringing it into the house, where resin could be transferred to rugs or to furniture. Handle the clothing as little as possible until it is soaked. Since urushiol can remain active for months, it's important to wash all camping, sporting, fishing or hunting gear that may also be carrying the resin.

* If you do develop a rash, avoid scratching the blisters. Although the fluid in the blisters will not spread the rash, fingernails may carry germs that could cause an infection.

Cool showers will help ease the itching and over-the-counter preparations, like calamine lotion or Burow's solution, will relieve mild rashes. Soaking in a lukewarm bath with an oatmeal or baking soda solution is often recommended to dry oozing blisters and offer some comfort. Over-the-counter hydrocortisone creams will not help. Dermatologists say they aren't strong enough to have any effect on poison ivy rashes.

In severe cases, prescription corticosteroid drugs can halt the reaction if taken soon enough. If you know you've been exposed and have developed severe reactions in the past, be sure to consult your dermatologist. He or she may prescribe steroids, or other medications, which can prevent blisters from forming.


Investigators have found that most people could be immunized against poison ivy through prescription pills. These pills contain gradually increasing amounts of active extract from the plants. However, this procedure can take four months to achieve a reasonable degree of "hyposensitization." In addition, the medication must be continued over a long period of time and it can often cause uncomfortable side effects. This procedure is recommended only if the doses are given before contact with the plant, and only for individuals, such as firefighters, who must live or work in areas where they come into constant contact with poison ivy. Consult your dermatologist for his or her advice on whether you should consider immunization.

Common Myths About Poison Ivy

* Scratching poison ivy blisters will spread the rash. This is not true. The rash is spread by urushiol on the hands--scratching the nose, for instance, or wiping the forehead--before blisters have formed.

* Poison ivy is "catching. " It's not. The rash cannot be passed from person to person--only urushiol can be spread by contact.

* Once allergic, always allergic. False. A person's sensitivity changes over time, even from season to season. People,who were particularly sensitive to poison ivy as children may not be allergic as adults.

* "Leaves of three, let them be." This is usually true, but not always.

* Dead poison ivy plants are no longer toxic. This is not true. Urushiol remains active for up to several years. Never risk handling dead plants.

* There's no immunization against poison ivy. There is, but it's not recommended--the procedure is tedious, and carries unwelcome side effects.

* Hydrocortisone creams will relieve poison ivy itches. They may help with very mild rashes, but, in most cases, these over-the-counter remedies are far too weak to combat the itch of poison ivy.
COPYRIGHT 1993 American Academy of Dermatology
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Publication:Pamphlet by: American Academy of Dermatology
Article Type:Pamphlet
Date:Jun 1, 1993
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