What is poison ivy / poison oak?

There are three related native American plants that can cause rashes: 

• poison ivy
• poison oak
• poison sumac

These plants can cause an allergic reaction in nearly 85 percent of the population. To be allergic to these plants, your child must first be "sensitized" to the oils. This means that next time there is contact with the plant, a rash may occur.

What causes an allergic reaction?