Poison ivy is the most common plants that cause a skin rash. More than half the people in the United States are affected with poison ivy. Most people are sensitive to poison ivy and these other plants to some degree. Poison ivy grows vigorously throughout much of North America. It can grow as a shrub up to about 1.2 m (4 ft) tall, as a groundcover 10-25 cm (4-10 in) high, or as a climbing vine on various supports.
The irritating substance is the same for each plant, an oily resin called urushiol. Simply brushing against a plant may not cause a reaction. On the other hand, you may develop dermatitis without ever coming into contact with poison ivy, because the urushiol is so easily spread.
Contact with poison ivy, oak, or sumac plants can cause a rash. Poison rashes are caused by the plants, called Rhus plants. The rash is caused by contact with the oil which is found in these plants. When your skin touches the leaves of a poison ivy plant, it may absorb some of the urushiol made by the plant. It takes only a tiny amount of urushiol to cause a reaction, but direct contact is essential. You may also develop a reaction indirectly if you touch urushiol left on an item, such as clothing, firewood or even a pet's fur. Burning poison ivy, poison oak or poison sumac can also cause a reaction because the smoke contains the oil.
A poison ivy rash will usually begin to appear 1 to 2 days after coming in contact with urushiol. The affected area will get red and swollen. A day or so later, small blisters will begin to form, and the rash will become very itchy. In severe cases, new areas of rash may break out several days or more after initial exposure. This may seem like the rash is spreading.
Prevention is the key to avoiding a poison ivy reaction. However, if you are aware that you came into contact with the plant, wash the exposed area immediately. Also, wash your clothes and any other gear that came into contact with the plant.
The best and safest treatment for Rhus rashes is wth a natural treatment such as Sumactin or with manganese sulfate solution. Manganese sulfate solution has been shown to be effective both to inactivate urushiol on the skin and to relieve itching. Manganese sulfate solution probably acts as a chelating agent for detoxification of urushiol.
Without treatment with steroids, the rash may not go away for up to three weeks without treatment, many children will have worsening symptoms with each exposure, and that some areas of a child's skin that had less exposure to the poison ivy plant will get the rash later than others.