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A Rash of Itchiness
(Poison Ivy)

By Dr. Peter W. Kujtan, B.Sc., M.D., Ph.D.

Article originally printed in the July 19, 2003 issue,
Reprinted in the July 23-24, 2005 issue,
on page 16 in the August 23-24, 2008 issue
and on page 39 in the June 23, 2010 issue of
The Mississauga News under the feature: Health & Beauty, Medicine Matters.

Poison Ivy and Poison Oak are two common Ontario plants from the Cashew Family that are the number one cause of contact dermatitis in North America. Poison Ivy is a three-leaf plant that can flower and has berries. It can grow as a shrub, and can climb or creep. The culprit is Urushiol oil contained in all parts of the plant.

Touching an intact plant is harmless, but these plants are fragile, and simply brushing a leaf can damage it and release the oil. Urushiol is one of the most allergenic substances known to man. Less than 1/100th of an ounce is enough to produce a break-out in every person in Canada! Any trace of Urushiol will produce an itchy weeping rash in 1-2 days.

Some people appear to have a natural immunity to it. This should not be confused with first time exposure which requires up to 10 days for the rash to develop. Some people will break out into an anaphylactic reaction within 4 hours. This group needs to get to the hospital immediately. For the avid gardeners it is interesting to note that an experimental vaccine has been in clinical trials with promising results.

Urushiol is an oily resin that binds to skin proteins. It can easily be removed with soap and water prior to binding. Time is of the essence. Once it binds, it attracts circulating T-cells which begin the cascade of an immune reaction. Blood vessels develop microscopic gaps which cause watery blisters. Scratching the rash and blisters will not spread the eruption. You need to spread the unbound oil to spread the rash.

Urushiol can remain dormant on clothes and gardening tools for years. I have seen mysterious laundry rashes attributable to minute oil traces on clothing. Attempts to destroy the plants with weed-wacking and burning can liberate the oil. The oil can also be carried in soot. Wash exposed clothes and implements as soon as possible with soap and water.

There are chemicals on the market such as Bentoquantum that may be used to minimize exposure, but keeping skin covered works better. Unless you are vigilant, you will only realize exposure in hind sight. Once you do recognize a break-out, try using calamine lotion and anti-histamines to minimize itching. A mild over the counter steroid cream can be started in a pinch. Topical anesthetics and oatmeal baths also help.

A more severe reaction will require a trip to your doctor for more potent steroids. One of the most common treatment failures is a rebound phenomenon. Patients stop their medicines once they appear to get better, only to have the rash come back in a week or two! In some people, repeated exposure does reduce the reaction while in others it intensifies. It is certainly worth the time to learn how to identify this common culprit found all over our region.

Related resources:

Poison Ivy: The Scourge of the Trail. Hike Ontario Fact Sheet 17.

Poison Ivy, Oak, and Sumac Information Center. Fast Facts, Pictures, Products, Remedies / Treatments, Q&A Board, Viewer FAQ, FAQ, General Info, Control.

Poison Ivy Fact Sheet from Kent County Health Department.

What Poison Ivy Looks Like.

Poison ivy from Wikipedia, the free encyclopedia.

Poison ivy - oak - sumac rash from MedlinePlus.

Poison Ivy, Oak, Sumac Factsheet from Texas Department of Insurance, Division of Workers’ Compensation (TDI/DWC).

Poison Ivy Fact Sheet from Maine Medical Center. Distinguishing Characteristics – “Leaves of three let them be”. Toxicity. Potential Exposures, Symptoms. Treatment. Prevention.

Poison Ivy Treatment Guide from About.com.

Other Articles by Dr. Kujtan