Poison ivy, poison oak, and poison sumac are three of the most common causes of allergic skin reactions (contact dermatitis) in North America. When these plants cause a skin reaction, it is called Rhus dermatitis.
These plants, from the genus Toxicodendron (which means "poison tree"), produce oil called urushiol, which triggers the allergic reaction. Patients who are allergic to these plants may experience a rash that consists of swollen, itchy, red bumps, and blisters that appear wherever the oil has touched the skin. The oil may also cause an allergic reaction if it is transferred from pets, clothing, shoes, camping gear, or gardening tools to the skin.
These plants grow in wooded areas (forests) throughout the United States, except for Alaska, Hawaii, and some areas of Nevada. The itchy and sometimes painful rash caused by contact with these plants occurs most frequently during the spring, summer, and early fall, when individuals are most likely to spend time outdoors.
An estimated three out of four people are allergic to the oil found in these poisonous plants, according to experts, although the degree of sensitivity varies among individuals. Some people will experience a quick reaction immediately after coming into contact with very small amounts of urushiol, while others may require large amounts of urushiol for a reaction to develop.
Researchers estimate that 85% of all people will develop an allergic reaction to poison ivy if they are adequately exposed to the oil. Adults who have not been exposed to poison ivy only have a 50% chance of developing an allergy to poison ivy. For unknown reasons, about 15% of people appear to be resistant to developing an allergic reaction.
The saying, "Leaves of three, let it be," is often used to describe the physical appearance of poisonous plants. However, not all three-leaved plants contain urushiol, and some that are poisonous have more than three leaves. For instance, while poison ivy usually has three leaves, they may also appear in groups of fives or sevens.
Individuals should learn what each of these plants looks like in order to prevent coming into contact with them. Topical creams like bentoquatam (IvyBlock®), are available over-the-counter and may help prevent or reduce allergic rashes caused by poison plants. If individuals suspect they have come into contact with any of these plants, they should wash exposed skin with soap and water.
Allergic individuals usually develop the rash within 24 to 48 hours after contact with the oil. However, it can take up to several days for the rash to appear. The rash will heal on its own in about five to 30 days, depending on the severity of the symptoms. If symptoms are mild, a cool shower, cool compress, or cool bath with baking soda or oatmeal may help relieve the itching and dry blisters. Medications, such as hydrocortisone or antihistamines, may help relieve itching and swelling. If the rash covers a large area of the body, or it is near the eyes, a healthcare provider may prescribe oral corticosteroids to reduce inflammation and itching.
Some individuals may develop a severe, life-threatening reaction called anaphylaxis. The most serious symptoms of anaphylaxis include low blood pressure, breathing difficulties, shock, and loss of consciousness. Anaphylaxis is a medical emergency that requires immediate treatment with a medication called epinephrine.
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types of plants
Poison ivy: The Latin name for poison ivy is Toxicodendron radicans. This plant may grow as a vine on trees and other surfaces, up to about 50 feet high. It may also grow as a shrub, reaching a height of about four or five feet.
Poison ivy is a hardy plant that can grow in many different conditions. It thrives in areas like sand, stony, or rocky shores of streams, rivers or lakes. It is also commonly found in thickets along the borders of wooded areas and in forest openings.
Poison ivy leaves are typically arranged in groups of three, but the leaves may also appear in groups of five or seven. The leaves in each cluster are about the same size, ranging from one-half inch to two inches long. The edges of the leaves may be slightly notched or smooth. The leaves are shiny and turn bright red in the fall.
Poison ivy produces flowers, which are yellowish to greenish white and about one-quarter inch wide. These flowers grow in clusters on a thin stem.
Small, berry-like fruits appear after the flowers have faded. These fruits are white or green in color and about one-sixth of an inch wide.
Poison oak: The Latin name for poison oak is Toxicodendron diversilobum. This plant has leaves that are lobed like those of an oak tree. Poison oak leaves are slightly larger than poison ivy's, and they grow in clusters of three, five, or seven. The plant's flowers and fruit are also similar to those of poison ivy. Poison oak may grow up to three feet high as either a shrub or a vine. Poison oak leaves have short, smooth hair on the undersides. This plant also produces berries, which are fuzzy and white. Even though poison oak loses its leaves during the winter, the plant remains poisonous year round because the vines also contain urushiol.
Poison sumac: The Latin name for poison oak is Toxicodendron vernix. This poisonous plant is less widespread than poison ivy and poison oak. The plant is most common in the Midwest. It can grow as tall as a tree or shrub with clusters of seven to 13 leaves. The leaves are arranged in pairs, with one leaf at the end. Poison sumac also produces small, yellowish flowers that grow in clusters. The flowers mature into berries that are white to green in color. Clusters of berries may grow up to 12-inches long.
There is also a species of sumac that is not poisonous. The nonpoisonous sumac plant has red berries.
procedure after exposure
Clothing should be removed and washed with detergent in warm water. Dry cleaning clothes will also eliminate the oil from clothing.
Wash all exposed areas of skin with soap and cool water. Using soap and water within 30 minutes of possible contact may prevent an allergic reaction. In the woods, water from a stream may effectively wash away the oil. Using water alone within five minutes of possible contact with the plant may prevent an allergic reaction.
Bathe pets exposed to the plants.
Wash any camping gear, garden tools, or other items that may have come into contact with urushiol.