P­oison Ivy, Poison Oak & Poison Sumac

Poison ivy, poison oak, and poison sumac grow almost everywhere in the United States, except Hawaii, Alaska, and some desert areas in the Western U.S. Poison ivy usually grows east of the Rocky Mountains and in Canada. Poison oak grows in the Western Uni­ted States, Canada, Mexico (western poison oak), and in the Southeastern states (eastern poison oak). Poison sumac grows in the Eastern states and southern Canada.

A Plant Induced Rash:

A plant induced rash is an allergic contact dermatitis caused by contact with oil called urushiol. Urushiol is found in the sap of the poisonous plants like poison ivy, poison oak, and poison sumac. It is a colourless or pale yellow oil that oozes from any cut or crushed part of the plant. Once exposure to air, urushiol turns brownish-black in colour. Damaged leaves look like they have spots of black enamel thus making it easier to recognize and identify the plant. Contact with urushiol can occur in three ways:

  • Direct contact – by touching the sap of the toxic plant.
  • Indirect contact – by touching something on which urushiol is present. This oil can stick to the fur of animals, to garden tools, sports equipment, or to any objects that may have come into contact with it.
  • Airborne contact – by burning the poison plants. This will release the urushiol particles into the air.

When urushiol gets on the skin, it will begin to penetrate in minutes. A reaction appears, usually within 12 to 48 hours. There is severe itching, redness, and swelling, followed by blisters. This rash is often arranged in streaks or lines where the person brushed against the plant. In a few days, the blisters will become crusted and take 10 days or longer to heal. Poison plant dermatitis can affect any part of the body. The rash does not spread by touching it, although it may seem to when it breaks out in new areas. This may happen because the urushiol absorbs more slowly into skin that is thicker, skin such as on the forearms, legs, and trunk.

Is everyone sensitive to this chemical?

Sensitivity may develop after the first direct skin contact with urushiol oil. An allergic reaction seldom occurs on the first exposure. A second encounter may produce a reaction which can be severe. About 85 percent of the population will develop an allergic reaction when exposed to poison ivy. The sensitivity will vary from person to person. For people who reach adulthood without becoming sensitive, they will then have only a 50 percent chance of developing an allergy to poison ivy. However, only about 15 percent of the population seems to be resistant.

Sensitivity to poison ivy tends to decline with age. Children who have reacted to poison ivy will probably find that their sensitivity decreases by young adulthood without repeated exposure. People who were once allergic to poison ivy may even lose their sensitivity later in life.

Recognizing Poison Ivy, Poison Oak and Poison Sumac:

Identifying the poison ivy plant is the first step to avoid the rash. The popular saying leaves of three, beware of me is a good rule of thumb for poison ivy and poison oak but is only partly correct. A more exact saying would be leaflets of three, beware of me, because each for poison ivy and poison oak each leaf has three leaflets. Poison sumac has a row of paired leaves. The middle or end leaf is on a longer stalk than the other two or more leaves.

Unfortunately, Poison Ivy has different forms. It grows as vines or low shrubs. Poison oak, with its oak-like leaves, is a low shrub in the East and can be a low shrub or a high shrub in the West. Poison sumac can be a tall shrub or a small tree. The plants also differ in where they grow. Poison ivy tends to grow in fertile, well-drained soil. Western poison oak requires a great deal of water, and Eastern poison oak prefers sandy soil and will sometimes grow near lakes. Poison sumac tends to grow in standing water, for example; peat bogs.

These plants are most common in the spring and summer. When they grow, there is plenty of sap and these plants will bruise easily. The leaves may have black marks where they have been bruised. Although poison ivy rash is usually a summer complaint, cases may occur in winter when people burn wood to clear yards that has urushiol on it, or cut poison ivy vines for wreaths.

It is important to recognize these toxic plants in all seasons. In the early fall, their leaves can turn colors such as yellow or red while other plants are still green. The berry-like fruit on the mature female plants will also change color in the fall; from green to off-white. In the winter, the plants will lose their leaves. And in the spring, poison ivy has yellow-green flowers.

Prevention of Poison Rashes:

Prevent the misery of a poison rash by looking out for the poison plants and staying away from them. You can destroy these weeds with herbicides in your own backyard, but this will not be practical when you are working in the field. If you are going to be in areas where you know these poison plants will likely be growing, wear long pants, long sleeves, boots, and gloves. Remember that the plant s oil, urushiol, will stick to almost all surfaces, and it does not dry. Therefore, do not let pets run through wooded areas since they may carry home the urushiol on their fur. Since urushiol can travel in the wind if the plants are burned in a fire, do not burn plants that look like poison ivy, poison oak or poison sumac.

Barrier skin creams such as a lotion containing bentoquatum offer some protection before contact with poison ivy, poison oak, or poison sumac. Over-the-counter products prevent urushiol from penetrating the skin. Ask your doctor or pharmacist for details.


If you think you ve had a brush with poison ivy, poison oak, or poison sumac, follow these simple steps:

  • Wash all exposed areas with cold running water as soon as you can reach a stream, lake, or garden hose. If you can do this within five minutes, the water may keep the urushiol from contacting your skin and spreading to other parts of your body. Within the first 30 minutes after coming into contact, soap and water are helpful to eliminate or reduce the rash.
  • Wash your clothing in a washing machine with detergent. If you bring the clothes into your house, be careful that you do not transfer the urushiol to rugs or furniture. You may also dry clean contaminated clothes. Because urushiol can remain active for months, wash all camping, sporting, fishing, or hunting gear that was in contact with the oil.
  • Relieve the itching of mild rashes by taking cool showers and applying over-the-counter preparations like calamine lotion or Burrow s solution. Soaking in a lukewarm bath with an oatmeal or baking soda solution may also ease itching and dry oozing blisters. Over-the-counter hydrocortisone creams are not strong enough to have much effect on poison ivy rashes.

Prescription cortisone can halt the reaction if used early. If you know you have been exposed and developed severe reactions in the past, consult a dermatologist or doctor. They may prescribe cortisone or other meds that prevent blisters from forming. If you use a cortisone treatment you must use the cortisone for longer than six days or the rash may return.

The Plants – Learn to Recognize Them:

As you can see from the pictures below, a plant induced rash could ruin your field work for the entire field season. Learn to recognize these plants so that you can avoid them!

Poison Oak (Above)

For more information on poisonous plants, please go to the following site:  http://www.cdc.gov/niosh/topics/plants/

All images are reprinted with permission from Jones & Bartlett Publishers,
Wilderness First Aid: Emergency Care for Remote Locations, 1998