May 18, 2015: What’s the important information to know about poison ivy, sumac and oak?

We find ourselves in the time of year where grass and flowers are growing, but so are those Toxicodendrons: poison ivy (Toxicodendron radicans), poison oak (Toxicodendron toxicarium, Toxicodendron diver-silobum), and poison sumac (Toxicodendron vernix).  In the United States, these are the cause for most common allergic reactions. Approximately 10-50 million Americans will develop and allergic rash after being exposed. Unfortunately, these poisonous plants are pretty much everywhere in the U.S., except Hawaii and Alaska. There are myths and tales associated with exposure, who is allergic and what’s the best treatment. This will be a quick insight into these pesky plants and clarification on some of these questions.

The antigenic oleoresin, urushiol, is the culprit responsible for the hypersensitivity dermatitis. These catechols are haptens that penetrate the skin almost immediately after exposure and bind with proteins. In turn, the immune system makes antibodies and these are what get activated in each subsequent exposure causing symptoms. These antigens are essentially identical in all these plants and cause cross-sensitivity. An allergic reaction seldom happens after the first time someone is exposed. However, a second exposure could cause a severe reaction. Only about 15 percent of people are resistant to these plants and sensitivity decreases with age.

Prevention is the best defense against a reaction. If there’s a risk for exposure, wear long pants, long sleeves, gloves and boots. Wearing rubber gloves is not beneficial for preventing dermatitis, as catechols are soluble in rubber. Next, wash thoroughly with soap and lukewarm water, as quickly as possible, after a potential contamination. It is estimated that 100% of the oils can be washed away if decontamination happens within the first 15 minutes of exposure and decreases to 0% by 1 hour post exposure. Avoid contact with plants that appear dead as they still have urushiol for years.

Antigens aren’t in the vesicles from the rash. Therefore, it isn’t spread or transmitted if they erupt. Transmission occurs from the urushiol in the sap and it doesn’t dry, even after coming in contact with objects. So, if the oils are on your clothes, your pet, under our fingernails or left on your skin, you can re-expose yourself or contaminate others. Although dermal route is the most common route referred to with exposures, it can also be harmful if ingested or inhaled.

As previously mentioned, urushiol is absorbed quickly and can be absorbed within 30 minutes. Rash typically appears within 24-48 hours after contact, but can be as early as 8 hours or delayed for up to 2 weeks. Avoiding contact is the best solution. Bentoquatum may be effective against exposure if used as a barrier. Decontamination would be the next line of defense. Once an exposure has occurred, topical steroids and antihistamines are the mainstay for treatment. Prescription cortisone can halt the reaction if used early. Unfortunately, once the vesicular stage has started, treatment with systemic steroids is the only effective solution. Oatmeal baths and cool showers may also be helpful with pruritus.

  • 1st picture-poison oak
  • 2nd picture-poison sumac
  • 3rd picture-poison ivy




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This question prepared by: Renee Miller, RN, MSN, CSPI with the Tennessee Poison Center


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Donna Seger, MD

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Tennessee Poison Center

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