Poison Ivy

Poison ivy (Rhus dermatitis) is a "feature" of summer. It isn't hard to diagnose: it's characterised by linear streaks (lines) of extraodinarily itchy (pruritic) vesicles where the plant leaves have brushed against the skin. Contrary to what you might think, fluid from ruptured skin blisters does not spread the eruption; however, the plant oil which is still present on the skin, under the fingernails, and on clothing can cause new areas of eruption if it isn't removed by washing with soap and water. The plant oil (oleoresin) may also be carried by animals on their fur, so petting or hugging a dog that has been rolling around in the woods can result in the classic poison ivy rash with no obvious history of exposure. All parts of the plant contain the sap, and the allergen (urushiol) is present on live or dead leaves, which means you must use caution cleaning out old plant material in the fall and winter. Watch out - burning this material can produce smoke with the oil in it, which can cause extensive eruptions. The eruption may appear as quickly as 8 hours after contact or may be delayed for a week or more. That is why poison ivy appears to spread - the areas exposed most intensely erupt first, and the areas just barely touched break out later.

Use cold wet compresses during the acute blistering stage. They are highly effective and should be used for 15 to 30 minutes several times a day for 1 to 3 days until blistering and severe itching is controlled. Topical steroids do not penetrate through blisters.

Short, cool tub baths with or without Aveeno® are very soothing. Calamine lotion controls itching but prolonged use causes excessive drying. Hydroxyzine (Atarax®) and diphenhydramine (Benadryl®) help control itching and encourage sleep.

Hydrocortisone 1% cream, available over the counter as Cort-Aid® or any number of other brands, is helpful to reduce the inflammation and itching. A stronger prescription preparation may be necessary. Prednisone or similar steroids are used orally for severe, widespread inflammation. Alternatively, a steroid injection can be given. Children who initially don't look too bad may get worse over the next few days and parents need to call their child's doctor if the condition worsens dramatically.

Poison ivy and poison oak are of course neither ivy nor oak species. Sensitization to one plant in the Rhus family produces cross-reactions with the other plants in the family - notably poison sumac and poison oak.

There is unfortunately no real preventative treatment; just avoid exposure if you can. Washing the skin with any type of soap inactivates and removes all surface oleoresin; it is most effective if done within 15 minutes of exposure, so if you think you or your child has been exposed, thoroughly scrub with soap and water as soon as possible and change clothes.

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