Doc Talk: What to do when poison plants cause allergic skin reactions

05/06/2013 1:28 PM

08/08/2014 10:16 AM

It’s that time of year when vegetation is growing quickly, including poison ivy, poison sumac and poison oak. These notorious plants cause more allergic skin reactions (contact dermatitis) than all other plants combined. The substance that leads to the allergic reaction is called urushiol, a colorless oil in the leaves, fruit, stem, root and sap of the plant. When exposed to air it turns brown and will sometimes leave brown spots on the leaves.

Contact dermatitis can affect all skin types. A person can be exposed to the oil in multiple ways, including direct contact with the parts of the plant described above, breathing in smoke of burning plants, touching clothing that has been exposed, or touching an animal that has been exposed.

The symptoms of contact dermatitis include intense itching, swelling, redness and blister formation. Symptoms typically occur several hours to a few days after exposure to the plant oil. Symptoms can last a few days or up to three weeks. Blister formation can occur over many days and does not mean that the rash is spreading. Fluid that leaks from the blisters is not contagious. The rash itself is not contagious either. The rash can be transferred to another person only if the oil is still on the body. This is why it is very important to clean all clothing, bedding and objects that the person has come in contact with.

To diagnose contact dermatitis, your doctor will examine the rash; no specific testing is needed. There are various treatment options. Antihistamines such as diphenhydramine (Benadryl) don’t provide much relief from itching, but can cause sleepiness. Better sleep may provide respite from the itchiness. Calamine lotion can help alleviate itching. Medications such as Domeboro and Burow’s solution can help reduce weeping of blisters and relieve the itching. Topical steroids are often used to reduce inflammation and itching. Over-the-counter hydrocortisone usually isn’t as helpful as stronger topical steroids that can be prescribed by your doctor. Occasionally, steroid pills such as Prednisone are prescribed if the rash is widespread. Topical antibiotic creams, antihistamines and anesthetics should not be used as they have the potential to make the rash worse.

The best way to prevent contact dermatitis is to simply avoid the plants that cause it. Follow the adage: “Leaves of three, leave them be.” If you know you will be in an area with a lot of vegetation, wear long- sleeved clothing, pants and gloves to protect your skin. If you do come into contact with poison ivy, you should wash your skin immediately, within less than 15 minutes. Be sure to wash gently and don’t rub or scrub the skin.

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