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Poison Ivy: Facts and myths

By Jim Crawford

I had a client call in needing information on poison ivy. It seems he thought winter would be a good time to get rid of some vines “because only the leaves cause irritation.” He has since learned that is a myth. Each year I receive several inquiries about poison ivy so I thought it was time to lay to rest some of the myths of these plants.

MYTH: Poison ivy and poison oak only grow as small shrubs or vines.

FACT: Both plants are in the Sumac family. Both normally grow as shrubs from 3 to 10 feet tall, but they also grow as woody vines that twine around trees and larger shrubs. These vines can be up to 6 inches in diameter.

MYTH: Poison ivy and poison oak are hard to identify.

FACT: They actually are readily identified by their leaves. The leaves grow in groups of three on a common stem and resemble oak or ivy leaves. Each of the three slightly glossy, sharply pointed green leaflets of poison ivy has a stalk. Poison oak leaves have a more rounded tip with the leaves resembling an oak leaf. The undersides of poison oak leaves are covered with hair and are always a lighter green than the tops. Only the center leaflet on poison oak has a stem. The general rule to remember is “Leaves of three, let them be!”

MYTH: Only the leaves can cause an irritation.

FACT: All parts of the plants except the pollen contains an extremely poisonous substance called urushiol. Poisoning occurs when this oil comes into contact with the skin causing painful irritation and blistering. Sensitivity to this irritant is acquired by repeated exposure to the plants. It may take 6-10 exposures to the toxin before you develop a sensitivity great enough to cause an irritation. The bad news is once you have developed this sensitivity, any exposure is likely to cause a breakout.

MYTH: Your skin starts to break out immediately upon being infected.

FACT: Symptoms can begin within a few hours after contact or can arise 3 to 5 days later depending on one’s sensitivity and the extent of contact. The oil must penetrate the skin before it can start to work. Irritation rarely occurs on the palms, scalp or soles of your feet because the outer skin in these areas is very tough and difficult for the oil to penetrate. If you wash the oil off your skin before it penetrates (within 5 minutes) the reaction can either be avoided or greatly reduced. Since this toxin is oil based, simply rinsing off with water will tend to spread the oil around increasing the area of exposure. A strong soap with COLD water, alcohol or bleach is best to break down the oil and remove it from the skin surface. Once the oil penetrates the skin, washing will not improve the situation.

MYTH: Scratching the blisters or the fluid oozing from the blisters will spread the poison to other parts of the body.

FACT: The liquid in the blisters is body fluids and can not spread the rash. If the chemical has not been completely washed off the skin, touching affected areas and then another part of the body can transfer the chemical and thus the rash. Similarly, the rash can not be passed between people unless the chemical is present. The major harm that comes from scratching the affected areas is the risk of infection. Scratching opens the skin surface and can allow infections to develop.

MYTH: The rash and itching lasts several weeks.

FACT: The rash is usually self-limited – it is at it’s worst after about 5 days and gradually improves within a couple of weeks. At first, the skin that has been exposed becomes red, and then bumps and blisters appear. This is usually accompanied by itching and sometimes swelling. After reaching their peak in several days, the blisters break and oozing sores begin to crust over and disappear.

MYTH: Burning is a good way to get rid of poison ivy or poison oak.

FACT: Smoke from burning these plants can be extremely harmful. The oil is not volatile at bonfire temperatures, however droplets of oil on the ash can transmit the rash to the skin. Inhalation of such smoke can result in poisoning the lungs that can require hospitalization.

MYTH: The oil is not longer dangerous after a few hours.

FACT: The oil can remain toxic for up to a year and some sources say 5 years! All tools and equipment should be thoroughly washed after exposure to the toxin. All clothing that has become contaminated should be isolated and washed separately from other clothing. Clothes should be washed two to three times with hot water, soap and either bleach or ammonia to ensure the oil is removed from the clothes. You should then rinse the washer by running it with no clothes in the tank to ensure all oil is removed from the system.

For more information stop by your University of Missouri Extension office and ask for MU Guide Sheet G4880 Poison Ivy: Identification and Control.

Jim Crawford is a field specialist in Agricultural Engineering for the University of Missouri Extension.