Poisonous plants Symptoms and Causes


All three plants cause an allergic skin reaction (contact dermatitis) by the same mechanism of action. Poison ivy, oak, and sumac all contain an oil called urushiol. This oil is not actually a poison, but it is made of chemicals that are allergens (substances that can cause an allergic reaction).
Typically, an allergic response is not triggered the first time the body encounters the allergen. In fact, some people can be repeatedly exposed to the allergen before an allergy develops. The first time or several times after the body is exposed to an allergen, the immune system becomes sensitized. During this process, the body's white blood cells develop immunoglobulin E (IgE) antibodies to the allergens in the plant oil. Once sensitized, the antibodies quickly detect and bind to the urushiol allergens in the body. These antibodies also trigger the release of chemicals (like histamine) that cause allergic symptoms like runny nose, watery eyes and sneezing, as well as anaphylaxis. Anaphylaxis is a systemic allergic reaction, which means that many parts of the body are affected. Symptoms of anaphylaxis can vary from mild to severe and may be life threatening. The most dangerous symptoms are low blood pressure, breathing difficulties, shock, and loss of consciousness, all of which can be fatal.
Urushiol is present in the stems, leaves and roots of these plants. The oil is released when the outer layer of the plant is broken. Even the smallest scrape or break in this layer can release the oil.
While these plants can cause allergic reactions year round, it is most likely to occur during the spring and summer, when the leaves are tender or bruise easily.
Individuals do not have to touch the plants directly to develop an allergic reaction. The oil is sticky and long lasting. It can be carried on clothing, shoes, or pets. The oil can then be transferred onto the skin and cause an allergic reaction.
Even in very dry conditions, the oil can still cause a reaction for several years. Dead plants can also cause an allergic reaction.
An allergic rash may develop immediately after contact with the oil or several days after contact.
The rash caused from these poisonous plants is not contagious. The rash can only be spread to other parts of the body or to another person if the oil comes into contact with the skin. Neither the blisters on the skin nor the fluids they secrete contain urushiol. Sometimes, if more than one area of skin comes into contact with the skin, one area will develop a reaction quicker than another. This is because certain areas of the skin are thicker than others. Individuals who develop a rash are advised to wash exposed areas of skin with soap and water to prevent the rash from spreading.
Inhaling smoke from burning poisonous leaves can cause an allergic reaction in the airways and lungs. This can cause difficulty breathing, and blisters inside the lungs that may be very painful. Individuals should seek medical care immediately.


The rash from poison ivy, oak, and sumac usually develops within 24 to 48 hours after contact with the oil. However, it can take up to several days for the rash to appear.
A red, itchy and bumpy rash develops on areas of the skin where oil touched. The rash develops the quickest on parts of the body where the skin is the thinnest (like the wrists, ankles, neck, and face).
The worse phase of the rash typically occurs within one week of exposure. During this time, itching may be severe. The bumps on the skin turn into blisters, which may secrete a clear, yellowish fluid. Within a couple weeks, the blisters begin to crust over and dry up as the rash subsides.
Depending on how severe the rash it, it may take anywhere from five to 30 days for the rash to completely resolve.


An allergic reaction to a poison plant is diagnosed when patients experience the typical allergic symptoms and develop the characteristic rash on the skin. Affected areas of the skin will be red and itchy. Oftentimes, the rash appears in patches or streaks where the plant brushed against the skin. Red bumps and oozing blisters may also be present.


Some individuals may experience a severe allergic reactions to poison ivy, oak, or sumac. If the rash covers more than one-quarter of the body, the allergens in the plant oil may cause a systemic reaction called anaphylaxis. Symptoms of anaphylaxis can vary from mild to severe and are potentially deadly. The most dangerous symptoms are low blood pressure, breathing difficulties, shock, and loss of consciousness, all of which can be fatal. Patients should seek medical attention immediately if they experience a severe rash, as well as fever, headache, or nausea, trouble breathing or shortness of breath, extremely painful rash that interferes with normal activity, or enlarged lymph nodes.