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Skin Rashes Due to Poison Ivy, Poison Oak and Poison Sumac

By: Dr. Brett Wilson

Poison ivy, poison oak and poison sumac are plants that occur throughout the southeast (though poison sumac tends to be in boggy areas). The rashes they cause are not distinguishable from each other so the poison ivy rash will look just like the poison oak or poison sumac rash. Contact with the oil (called urushiol) in leaves and other parts of these plants causes more cases of allergic skin reactions/contact dermatitis than all other plant families combined.  The rash is typically itchy and can present in many forms with streaks of redness, large or small patches of redness and even small or larger blisters.  The rash can only develop where the oil can touch skin and so it is usually occurs on areas not covered by clothing (hands, neck, face, arms and legs) and where one is touched by one’s hands (eyes, face, genital region).  But the oil can also penetrate thinner clothing and thus can occur on areas even covered by t-shirts. The rash can also develop from touching something that has the oil on it such as the fur of a pet or garden tools or even the smoke from the plant if it is burned. The skin of mangoes and ginkgo fruit also contain urushiol and can produce symptoms similar to poison ivy.  The rash and/or blisters can occur on some skin areas days before other areas of the body but this does not mean that the reaction is spreading from one place to another and it does not spread in the bloodstream.  Also, the fluid that leaks from blisters does not spread the rash.  The rash is not contagious to others so one can only get the rash by direct contact with the plant oil. The rash can last up to 3 weeks but may resolve more quickly with medical treatment (see below).

People of all ethnic backgrounds and skin types are at risk of developing a reaction after contact with the plant.  About 50 percent of people develop a rash after touching the plant but the time of the reaction can occur anywhere from 1 to 14 days after exposure. In people who have never been exposed before to the plant, it can even take up to 21 days to develop a reaction.  The severity of reaction to poison ivy tends to decrease with age. It is possible to get a rash at any time of the year including winter but can also be contracted by touching something that has the oil on it such as the fur of a pet or garden tools or even the smoke from the plant if it is burned. The skin of mangoes and ginkgo fruit also contain urushiol and can produce symptoms similar to poison ivy.

Learning to recognize the plants is a key step to avoiding getting a skin reaction. “Leaves of three, let them be” is a phrase used to identify poison ivy and poison oak as they have three leaves on a single stem. Poison sumac has 5, 7, or even up to 13 leaves per stem. But it is not always possible to identify the plants by leaves alone since the appearance can vary depending on the season, climate and growth cycle. And even if the plant is dead, the oil is still on the stem, root and sap of the plant. One other clue is that the leaves can often have shiny black spots since the sap on leaves turns dark when exposed to air.

Prevention: Wearing long pants and socks in wooded areas as well as long sleeve shirts and gloves when doing garden, yard or forest work can help prevent exposure. To create a barrier between the skin and the plant oil, the use of creams or ointments such as Bentoquatam (Ivy Block is a brand name) may be helpful but it must be reapplied every 4 hours and leaves a clay residue on the skin.   Once done with activity that would involve poison ivy exposure, it is recommended to remove any contaminated clothing and place them into a bag or the washing machine directly to prevent spread of the oil.  Gently washing the skin and under fingernails with mild soap (harsh soaps are no more effective) and water as soon as possible can help prevent the rash. If the oil is on the skin longer than 10 minutes, then washing will not help very much and after 60 minutes, will not help at all. There is one over the counter product called Tecnu Extreme which will remove urushiol oil and also reduce symptoms from any developing rash. Keeping fingernails cut short can help prevent secondary infection.

Diagnosis and Treatments:  There is no diagnostic test for poison ivy and the diagnosis is based upon history and how the skin looks. Treatments are generally aimed at relieving itchiness, soreness and discomfort and to prevent secondary skin infection by preventing scratching.

Skin treatments: Adding oatmeal (for example Aveeno oatmeal packets) to a bath, applying cool wet compresses and applying calamine lotion may relieve itching. If blisters leak fluid, over the counter topical medications called astringents such as Burrow’s solution and Domeboro may relieve the rash as well.

Antihistamines: Benadryl (diphenhydramine) orally every 6 hours may help one to ignore the itching (by inducing sleepiness) but does not always actually relieve the itching. Zyrtec or Cetirizine may provide a similar benefit.

Steroid Creams: These are very useful when used during the first few days of symptoms but the over the counter strengths (1 percent hydrocortisone) are not generally effective and so prescription strength steroid cream is needed.

Oral Steroids:  If severe symptoms develop (large areas especially on the face and genital region), oral steroids for 7-21 days can relieve itching and swelling. On rare occasions, injections of a steroid may be necessary.

Skin infections (the rash lasting longer then 3 weeks or increasing in severity despite the above treatments, and white pus-like discharge or crusty yellow/orange scabs) are a potential complication of poison ivy due to scratching excessively and introducing bacteria. However, it is not recommended to use antihistamine creams/lotions, anesthetic creams containing Benzocaine, or antibiotic creams containing neomycin as these may make the rash worse. If an infection occurs, then prescription antibiotics (topical or oral) are typically needed to resolve the infection.


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