Ask Dr. Kent . . .

I had a patient come in the office today with a very itchy rash scattered on his hands, arms, and lower legs. It started to develop about 1 day after trimming his yard. When I examined the rash, I knew immediately that it was poison oak dermatitis. Poison oak, sumac, and ivy dermatitis are the most common causes of allergic contact dermatitis in the United States. The allergens in poison ivy and poison oak are contained in the resinous sap called urushiol. The sap is in all parts of the plant. Cashew trees, mango trees, Japanese lacquer trees and ginkgo are in the same plant family and they have allergens related to poison ivy.

Workers that harvest the cashews from the resinous nutshells often develop contact dermatitis. Dermatitis will develop when a person comes into direct contact with the resin on leaves, stems, or roots. How severe the dermatitis becomes depends on the amount of resin that touches the skin, a person’s susceptibility, and regional resin reactivity.

Dermatitis can range from mild redness of the skin to the development of vesicles. One can develop dermatitis from exposure to the smoke of burning plants. The dermatitis can develop as early as 8 hours after exposure to a week later. If one’s skin continues to come into contact with resin on clothing or pets, new areas can continue to develop.

A person can prevent the dermatitis by washing the skin immediately with soap and water. Soap will inactivate the resin. After 10 minutes, only 50% of the resin can be removed from the skin. No resin can be removed after 1 hour. Ivy-Block, an organockey compound, can prevent dermatitis in 50% of exposed patients by forming a barrier.

A person can use cold wet compresses on the dermatitis 15 to 30 minutes several times per day. An Aveeno Oatmeal bath can be soothing to the inflamed skin. Diphenhydramine and Hydroxyzine can help with itching. Calamine lotion can help with itching but can dry the skin over time. Topical steroids can be used to help with inflammation and itching. In severe cases of dermatitis from poison ivy or oak, oral steroids and or injection of steroids may be required.
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