Poison Ivy, Oak, Sumac

Medical Dermatology

Skin Conditions

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Poison ivy, poison oak, and poison sumac are the most common cause of allergic reactions in the United States. Each year 10 to 50 million Americans develop an allergic rash after contact with these poison plants. They 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.

Poison plant rash is an allergic contact dermatitis caused by contact with oil called urushiol which is found in the sap of poisonous plants like poison ivy, poison oak, and poison sumac. It is colorless or pale yellow oil that oozes from any cut or crushed part of the plant, including the roots, stems, and leaves. After exposure to air, urushiol turns brownish-black. Contact with urushiol can occur in three ways:


Direct contact

  • touching the sap of the toxic plant.

Indirect contact

  • touching something on which urushiol is present. The oil can stick to the fur of animals, to garden tools or sports equipment, or to any objects that have come into contact with it.

Airborne contact

  • burning poison plants put urushiol particles into the air.
     

When urushiol gets on the skin, it begins to penetrate in minutes. A reaction appears, usually within 12 to 48 hours. There is severe itching, redness, and swelling, followed by blisters which is often arranged in streaks or lines where the person brushed against the plant. In a few days, the blisters become crusted and take 10 days or longer to heal.

Poison plant dermatitis can affect almost 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 urushiol absorbs more slowly into some areas of skin and takes longer to break out there. Sometimes new lesions can keep erupting for weeks.

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

Identifying the poison ivy plant is the first step in avoiding the rash. The popular saying "leaves of three, beware of me" is a good rule of thumb for poison ivy and poison oak. Poison sumac, however, has a row of paired leaves. The middle or end leaf is on a longer stalk than the other two or more leaves. This differs from most other three-leaf look-alikes. 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 or high shrub in the West. Poison sumac is a tall shrub or small tree.

Prevent the misery of poison ivy by looking out for the plant and staying away from it. You can destroy these weeds with herbicides in your own backyard. If you are going to be where you know poison ivy likely grows, wear long pants, long sleeves, boots, and gloves. Remember that the plant¹s nearly invisible oil, urushiol, sticks to almost all surfaces, and does not dry. Do not let pets run through wooded areas since they may carry home urushiol on their fur. Because urushiol can travel in the wind if it burns in a fire, do not burn plants that look like poison ivy.

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 dermatologist 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, soap and water are helpful.
  • 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. Urushiol can remain active for months so wash 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 Zanfel, calamine lotion or Burow¹s 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 have developed severe reactions in the past, consult your dermatologist. He or she may prescribe cortisone or other medicines that can prevent blisters from forming. If you receive treatment with a cortisone drug, you should take it longer than six days, or the rash may return.