Poison ivy, poison oak and poison sumac are all capable of causing a rash called contact dermatitis. This is because all three plants contain an allergenic oil called urushiol in their leaves, flowers, berries, stem and roots. Poison oak can grow as a shrub or a vine and has three leaves similar in appearance to the leaves of an oak tree. Although all three poisonous plants are different, the rash they cause is the same. Identifying that rash is an important part of treating it.
Pay attention to your symptoms. If you develop an itchiness in a spot that you know for sure was in contact with poison oak, it is likely this is caused by a poison oak rash. That said, you do not have to have had direct contact with poison oak to develop the rash. Poison oak can be contacted through indirect contact when the oils are on your clothes, pet fur, sporting equipment, garden equipment or in the air from leaves burning.
Look at the rash to see if it looks like a poison oak rash. There will be red streaks or a general redness in the area in which the urushiol oil came into contact with the skin. There may also be small or large bumps called hives in various areas. In many cases a poison oak rash may also have blisters that ooze clear fluid.
Check to see if the rash has spread. A poison oak rash will not spread beyond the areas that have had direct or indirect contact with the urushiol oil. However, it is important to remember before you wash, when the urushiol oil is still on your skin it can be spread if you touch or itch or one area and then another. Additionally, it is not contagious. Anyone who gets the rash has had either direct or indirect contact with the urushiol oil.
Check for symptoms of a severe reaction. In many cases people can have a severe allergy to poison ivy, poison oak and poison sumac. In cases such as these they may develop swelling or widespread blistering.