Originally published in The Ottawa Citizen June 24, 2003
Original Title: Poison Ivy
During the summer months, it is common to see people come in with peculiar linear or blotchy blistered red rashes. Welcome to poison ivy country.
Poison ivy was named in 1609 by adventurer, explorer and president of the British colony of Jamestown, Capt. John Smith. It belongs to the cashew family.
Found in areas of southern Canada and parts of the United States, it grows as a vine on trees or as a bush in grassy or bare areas. Often you will encounter it along the edges of roads, footpaths or fields, a new shopping mall or a housing subdivision where it does not have to compete with other vegetation. Hiking trails in and around Ottawa-Gatineau post poison ivy warnings.
Poison ivy is readily identifiable. The leaves grow on the stalk in groups of three. Their colouration starts as red in the spring, changing to shiny green in summer, then yellow, red or orange by the fall. Poisonous white, waxy clustered berries appear later in the season.
Poison ivy is related to poison oak (Pacific Northwest and western Canada) and poison sumac (eastern United States). However, these plants are shrubs and have seven to 13 leaves per stem, unlike poison ivy.
The sap (oleoresin) from the vine or shrub, and urushiol oil (from the Japanese, urushi meaning lacquer) are intensely irritating to the skin. One billionth of a gram (a nanogram) will cause a rash. An affected person’s average exposure is 100 nanograms. To put this natural irritant’s strength in perspective, seven grams (a quarter-ounce) would be enough to cause a rash for everyone on Earth.
The oleoresin can remain active on any surface, including dead plants, for up to five years. Collecting firewood over the winter can inadvertently include the poison ivy vine. Burning the vine will release the urushiol into the air leading to lung and eye irritation.
Poison ivy rash is not an infection but a chemical irritation. The fluid within the rash’s blisters does not contain the oleoresin and will not spread the rash. It will spread from person to person if the hands or clothing remains contaminated with oleoresin. Washing the oleoresin from the skin, clothing and surfaces eliminates the risk of contaminating others.
About 50 to 70 per cent of the population is allergic to urushiol, especially those with cashew allergies. The rash appears 24 to 48 hours after contact with the resin. It quickly becomes red and intensely itchy. Blisters can form. Often, the rash appears in streaks where the vine has scratched the skin.
The rash usually resolves one to two weeks after exposure. Some people with no previous exposure to poison ivy will develop the rash seven to 10 days after exposure. Frequent exposure to poison ivy increasingly stimulates the allergic response and the rate of rash and blister formation.
There is a 10-minute window of opportunity after exposure when thorough soap and water washing of the skin can minimize the chance of a rash. Remove any clothing contaminated by the oil, and wash it thoroughly, being careful not to touch the clothes with your bare hands.
Treatment options depend on the severity and discomfort of the rash. The use of antihistamines, cool compresses, Aveeno colloidal oatmeal baths and topical steroid creams can limit mild to moderate reactions.
Do not intentionally break the blisters. They act as a protective covering for the healing skin underneath them. It can lead to secondary bacterial infections, complicating treatment and potentially worsen scarring. Consult your doctor if large blisters form on your hands. It may be necessary to drain the blisters to allow more freedom of movement, reduce hand stiffness and loss of function.
Wet-to-dry dressings on oozing blisters can dry them out so you can apply steroid creams. Your pharmacist can help prepare a Burow’s solution. Apply this solution to a single thin cotton sheet or fabric and apply it to the skin. Allow the fabric to dry over 30 minutes. Repeat the procedure several times. For those who suffer extensive skin damage, your doctor may prescribe a short-term course of oral steroids. The rash usually resolves within two to four weeks. Prevention is a matter of avoiding the plant. Pets — especially dogs — can pick up the resin on their fur, so be mindful after Greenbelt excursions.
© Dr. Barry Dworkin 2003