8 Myths and Truths About Poison Ivy, Oak, and Sumac

Myth #1: These plants are poisonous.
Truth: Poison ivy, poison oak, and poison sumac are all members of the Toxicodendron genus. All members of this group produce chemicals in their plant juices to which most human beings are able to develop a brisk allergic response. The first time one comes into contact with these chemicals there is generally no reaction but the immune system is stimulated to develop the capacity to recognize the molecule the next time a contact occurs.

Myth #2: One must come into direct contact with the plant to develop a rash.
Truth: Generally direct contact with plant juice is required. Occasionally reactions can occur if this juice is transferred indirectly onto the skin of a sensitive individual (for example, from the fur of a pet or clothing that has been contaminated with the plant oils). Sometimes blowing wind, especially soon after a brushfire, can contain enough chemical to cause a rash in very sensitive people.

Myth #3: The appearance of the rash is characteristic for Toxicodendron dermatitis.
Truth: There is nothing specific about the appearance of the eruption. Any other plant allergic contact dermatitis could potentially appear identical. The rash appears as red, itchy bumps and small blisters often distributed in a linear fashion on exposed surfaces. When the blisters rupture, there can be weeping and oozing.

Myth #4: The weeping blister fluid can spread the rash to someone else.
Truth: The only way to spread this rash from one person to another is by the transfer of the plant juice. The blister fluid generally does not contain the allergenic chemical so this is not likely to ever occur.

Myth #5: Individuals allergic to Toxicodendron can react to other members of closely related botanical groups.
Truth: This is true. The allergen present in this plant group is structurally similar enough to react to plant juices from other members of the family Anacardiaceae, like cashew nut oil, mango rind, and certain Chinese lacquers.

Myth #6: Allergic individuals can be desensitized by eating the leaves of the plant.
Truth: It is very difficult to desensitize an allergic individual to this family of chemicals.

Myth #7: Once the eruption occurs, there are a variety of treatments that easily suppress the reaction and can be performed without visiting your physician. They vary from applying human urine to the site of the eruption to drenching the skin in gasoline.
Truth: For mild local reactions, it is generally necessary to apply potent topical steroids to the site for two to three weeks. For more severe reactions, it is often necessary to take oral cortisone (prednisone) in the appropriate dosage for two to three weeks.

Myth #8: There are barrier creams which can be applied to the skin prior to potential exposures which can prevent the rash.
Truth: In the April 2001 issue of the Skin Therapy Letter, two products are mentioned that appear to have significant potential to act as a barrier to the chemical allergen: quaternium-18 bentonite cream (Ivy Block) and Stokogard cream.


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Lee, Nancy P., and Edgar R. Arriola. "Poison Ivy, Oak, and Sumac Dermatitis." Western Journal of Medicine 171 Nov./Dec. 1999: 354-355.