Poison Ivy & Other Poisonous Plants

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Risk Factors and Cause

Exposure to poison ivy, poison oak, and poison sumac can cause an allergic reaction. The characteristic itchy rash develops in response to contact with a substance called urushiol. This substance is present in the leaves, stems, and roots of the plants.

Reactions can occur following direct contact with the plant, through indirect contact (e.g., touching an object that has picked up urushiol from the plant, such as gardening tools and pet fur), and through airborne contact (i.e., burning the plants can release urushiol particles into the air).

People who spend time outdoors in areas where poisonous plants grow are at increased risk for developing an allergic reaction. Wearing long pants, long-sleeved shirts, and gloves while working outside can help reduce the risk. Washing exposed areas of skin with soap and water within 30 minutes of possible exposure also can reduce the risk. Clothes, tools, sporting equipment and other objects that may have come in contact with the plants should be handled with care and washed thoroughly.

Signs and Symptoms

Direct contact with poisonous plant for the first time causes sensitivity. In most cases, this exposure does not produce a reaction. Sensitivity to poison ivy varies from person to person. In some people, subsequent exposure results in a skin rash that develops within 12–48 hours.

Symptoms can be mild, moderate, or severe and include itching, redness (erythema), and blisters. The rash often is linear (i.e., appears in a line where the leaves of the plant have touched the skin). Blisters may ooze clear fluid and usually begin to crust over in a few days. In most cases, rashes caused by poison ivy, poison oak, and poison sumac heal completely in a week or two.

Poison ivy does not spread by touching the rash. In many cases, symptoms develop gradually on areas of the body that absorb urushiol more slowly. Rashes rarely occur on the soles of the feet or the palms of the hands because the skin is thicker in these areas.

In some cases, poison ivy, poison oak, and poison sumac can result in complications. Scratching may prolong the rash, can cause a secondary bacterial infection, and increases the risk for scarring. Complications also can occur when the toxin (urushiol) is inhaled into the nose and throat.

Other complications may indicate a severe allergy and include the following:

• Difficulty breathing or speaking (e.g., hoarseness)
• Dizziness or lightheadedness
• Swelling around the nose and mouth
• Tightness in the chest
• Widespread redness or swelling

Diagnosis

Diagnosis of poison ivy, poison oak, or poison sumac often is made on the basis of physical examination. In most cases, recent exposure to the poisonous plant, followed by observance of the characteristic rash is enough to make a definitive diagnosis.

Because poisonous plants can cause symptoms that are similar to other dermatologic conditions, a physician should be consulted. Physicians examine the area(s) of the body affected by the rash (called distribution) and the type, shape, and arrangement of the blisters.

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