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About 25-40 million Americans will need medical treatment post-exposure to poison ivy annually. All ethnicities and skin types are affected equally by poison ivy; however, children are often less sensitive than adults to the plant. Poison ivy is typically diagnosed clinically after medical history and a physical examination are taken. If necessary, a culture may be done if concern for secondary bacterial infection exists. 

What is poison ivy?

Poison ivy, a plant that is part of the toxicendron species, accounts for more allergic contact dermatitis rashes than all other plant families combined. There are many members of the toxicendron species which include common or northern poison ivy (toxicodendron radicans), western poison ivy (toxicodendron rydbergii), eastern poison oak (toxicodendron toxicarium), western poison oak (toxicodendron diversilobum), and poison sumac (toxicodendron vernix). This plant is found broadly throughout the United States. Toxicodendron means “poisonous tree”.

Poison Ivy on ground


The allergenic compound found in poison ivy is called urushiol. Not everyone is sensitive to the compound, about 50% of people will react to poison ivy when encountered in nature, and 75% reacting to patch testing with urushiol. Reactions can be started by direct contact with the plant, contact with objects contaminated with urushiol, or inhalation of fumes from burning poison ivy plants. The urushiol is a light, colorless oil which is present in all parts of the plant, including the fruit, leaves, stem, and root.

Broken plants are much more likely to cause the rash than intact plants, and the plants are easily broken by the wind, rain, and rubbing. Urushiol containing plant parts remain allergenic and irritants all year around. The allergenicity also can persist for years after the plant has died. The reaction occurs by first the urushiol penetrating through the top layer of the skin, where it is then taken up and processed by other cells, which then travel to the lymph nodes. 

Indentifying poison ivy

Identifying the plant before coming into contact with it will lower the risk of developing an allergic contact rash. The plants can be identified by three leaflets, where the saying “leaves of three, let them be” originates from. They also often have flowering branches. Poison sumac have leaflets of 5, 7 or more and it grows as a shrub or a small tree. It grows in standing water or swampy areas. Poison sumac may have black dots on them, which is oxidized urushiol. The poison ivy plant grows as a shrub in far Northern and Western United States, Canada and around the Great Lakes. It grows as a vine in the East, Midwest and South of the US. It may have yellow-green flowers or green berries. Poison oak has 3 small leaflets, grows as a shrub or a vine and may have yellow-white berries. It is recommended to familiarize yourself with pictures of the plants before spending time in forested areas. 

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Exposure to poison ivy

Camping, hiking, landscaping, firefighting, gardening, construction, farming, etc. all increase risk of poison ivy exposure. Avoiding the plants altogether is the best method to prevent exposure. Wearing protective clothing is helpful to prevent direct contact with the skin, such as long sleeves, long pants, boots, and gloves. Do be aware that clothing, pets, backpacks, shoes, shoelaces, jewelry, etc. can hold the urushiol on them. For example, if a piece of clothing were to have urushiol on it and was never cleansed, then it could cause an allergic contact rash years later.

Urushiol can remain active for years. We recommend using thick vinyl gloves when working in the yard, because latex and rubber gloves do not always protect against poison ivy. We recommend washing exposed clothes immediately in a washing machine with detergent (or a special preparation designed for poison ivy). Never burn a poison ivy plant because inhalation of the fumes can cause an allergic reaction. If you have poison ivy in your yard, you can apply an herbicide or remove the plant and root while wearing vinyl gloves.

Make sure to keep pets away from the plants, as their fur can harbor urushiol and if there is an exposure to wash their fur gently with soap and water. There has been shown to be some benefit of using an over-the-counter barrier cream with bentoquatam (5% quaterium, 18% bentonite lotion) which can be applied to the skin before going outdoors. However, even with this barrier cream it is recommended to wear protective clothing. Bentoquatum must be re-applied every four hours on the skin.

Poison ivy symptoms 

Symptoms of the rash include severe itching, redness, and small, fluid-filled blisters. The rash typically presents in a line or streaks consistent with brushing up against a poison ivy plant. If the contact was from pet fur or another method of indirect contact, then it may present differently.

Some people will experience hives and occasionally “black spot” dermatitis when the urushiol is left on the skin, causing black spots that cannot be washed off. The symptoms of the rash usually start within 4 to 96 hours post-exposure and peak between 1 to 14 days after exposure. If the rash is left untreated, it will typically resolve in 1 to 3 weeks.

If the dried black urushiol is left on clothing, tools, etc., it can put close contacts at risk of exposure as well.

New lesions can appear up to 21 days post-exposure in previously unexposed individuals. This may make it seem as if the rash is spreading, but it is not. Due to the rash disrupting the healthy skin barrier, people are at risk for secondary bacteria infection in the affected areas with skin bacteria, most commonly staph aureus.

After the rash has resolved, it can often leave behind a darker coloration in the skin called post-inflammatory hyperpigmentation, which is from the inflammation the rash caused. This coloration will return to the normal skin tone with time, but it can take months.

What to do

If you know you have been exposed to poison ivy, you should remove any contaminated clothing and wash the skin gently with mild soap and lukewarm water. After the first 10 minutes of urushiol exposure to the skin, 50% can be removed with soap and water. That percentage decreases as the urushiol is left on the skin longer. However, washing even two hours after exposure can greatly reduce the likelihood and severity of the allergic rash. Be sure to wash underneath your fingernails as well because the oil can be forgotten there. Experts advise not to scrub the area vigorously, as that can worsen the rash. 

All clothing that had come in contact with the plant should be washed with warm water and soap as well.

Yellow crusting and pus at the site of the rash can be signs of a skin infection. A culture may be taken as well to determine what bacteria is growing. With the increasing prevalence of resistant bacteria, a culture can help determine what antibiotics the bacteria are susceptible to or resistant to. If you develop difficulty breathing or swallowing, severe swelling, or fevers, then seek emergent care immediately. 

Treatments: Prescription and over-the-counter

Over-the-counter medication

Over-the-counter oatmeal baths and cool, wet compresses can help calm the itching. Treatment with creams containing menthol and phenol (calamine lotion) may also provide a cooling, symptomatic relief. Avoiding antihistamine creams and topical antibiotic creams is recommended, as these can irritate the skin further.

It is important to avoid scratching the rash because it will worsen the itch. If your rash has developed blisters, the blister or its fluid will not spread the rash. The rash is not contagious. Over-the-counter antihistamines such as Claritin, Zyrtec, Allegra, or Benadryl are not effective for the itch in poison ivy dermatitis because it is not caused from histamine release. However, antihistamines with the sedating effects, such as Benadryl, can help you sleep if the itch is keeping you up at night.

Prescription medication

Prescription-strength, high potency topical steroid creams such as Clobetasol are the most effective treatment in the early stages of the rash. If your rash is localized to a small area or has not been present for long, then your provider may prescribe a steroid cream. If your rash is more extreme or involving areas such as the face or genitalia, then your provider may prescribe an oral steroid medication such as prednisone for 2 to 3 weeks to help prevent recurrence of the rash after completion of the steroids.

Injections of steroid have not been well studied for their benefit in poison ivy dermatitis cases, but they may be helpful if the rash is not widespread. Steroids work by helping to reduce swelling and itching present with the rash; however, over-the-counter topical steroid creams are typically not strong enough to treat poison ivy dermatitis. We will evaluate you and determine if an antibiotic is necessary. 

Please visit our dermatology specialists at Regency  if you have a rash which you believe may be related to poison ivy exposure for further evaluation and treatment. 



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