Poison Ivy

General Information

Poison Ivy, poison oak, and poison sumac are plants found throughout North America except in desert regions and at high altitudes. Contact with these plants can cause a skin rash known as allergic contact dermatitis. 

The rash is caused by  urushiol oil produced which the plant produces. The oil is found in all parts of the plant including the leaves, stems, roots, flowers, and berries. Urushiol oil is an allergen which means it triggers an immune or allergic response when it comes in contact with skin. The rash is therefor an allergic rash and not really poisonous or infectious. The rash usually looks like red streaks where the plant brushed against the skin. There may also be small bumps and in more intense cases there may be larger fluid filled blisters. The rash is nearly always very itchy.

Important facts about the poison ivy rash

  • Because this is an allergic reaction it is not contagious despite the wide held belief to the contrary. Someone who has the oil on their skin can transfer the oil to someone else and they can get a rash but once the oil has been washed off the rash itself is not contagious.
  • An individual can not spread the rash around their own body by scratching it either although it may appear that this is happening since some portions of the rash may not become visible until  days after the first rash is seen.  
  • The rash can develop anywhere from a few hours to a few weeks after skin comes in contact with the oil,l but most people will react within a day or two. Each exposure seems to shorten the time period between exposure and development of the rash.
  • Because the rash is due to an allergic response to the oil not everyone is susceptible to it. Only those who are allergic to Urushiol will develop a rash. Some people do not react to the oil at all, however this can change over time. Repeated exposure can cause someone who is not initially sensitive to become sensitive so care should always be taken around poison ivy even if you have never reacted to it in the past.


The best way to prevent the rash caused by poison ivy is to avoid contact with the plant. This is easier to do if you know what the plant looks like. The two pictures above are examples of poison ivy. A search of google images will turn up lots of pictures of poison sumac and poison oak.

Poison Ivy can exist in different forms from small sprigs hiding among your bushes or in the grass to vines several inches thick climbing your trees. The smaller plants can be very difficult to see. If this is a concern it can be helpful to wear long sleeves and long pants to reduce the risk of exposure. Be careful to wash the clothes well afterward because even indirect contact with oil that got on the clothes can cause a rash. The oil is very stable and can remain active on an unwashed surface for many years. Dogs and cats can carry the oil on their fur if they come in contact with the plants. Unless the animal is washed the oil can remain there for a very long time and contact with the oil can cause repeated reactions to the pet owner. If one or more members of a household develop a poison ivy rash without any known contact it may be a good idea to bathe all household pets that have exposure to the outdoors even if they only go for an occasional walk outside.

What do you do if you brush against a poison ivy plant? If the area in question is quickly washed with soap and water the rash can be prevented or the severity reduced. Waiting more than 10 minutes to wash off may significantly reduce the chances of stopping the rash and after an hour washing may have very little effect at all.


  • Mild cases  - Mild cases usually involve a singe small patch of skin. These can be treated with cool compresses and over the counter antihistamines and cortisone creams. Other products like Solarcaine gel which have a numbing agent in them may also give temporary relief from the itch.
  • Moderate cases - These usually involve a single large area or several smaller areas. Treatment for these cases may require the use of prescription strength cortisone cream in addition to the measures mentioned above.
  • Severe cases - In these cases there may be several large areas of the body involved or there is swelling of the face. For these cases oral cortisone is almost certainly needed to reduce the itching adequately and allow the person to work and sleep comfortably. Antihistamines and topical agents may also be used but topical cortisone is not necessary.


The most common complication is the development of a bacterial skin infection caused by the breakdown of our natural barriers when blisters break open on the skin. Frequent scratching then introduces bacteria into these areas from non-strerile fingernails. If conditions are right bacteria will get under the skin and cause a skin infection known as cellulitis. For this reason it is important to keep the fingers as clean as possible and do everything possible to avoid scratching.