Your skin is one of the first parts of your body to come in contact with the environment. Contact with certain substances, however, can sometimes be harmful. For example, contact with the sap of either poison ivy, poison oak, or poison sumac plants, which contain an oily substance called urushiol, produces an allergic reaction in millions of people each year. This reaction is commonly referred to as poison ivy dermatitis.
As with any allergen, the first exposure to urushiol does not produce any outward reaction. Yet inside your body, the immune system is preparing for additional exposures. The immune response begins when white blood cells engulf and destroy the allergen. As the allergen is destroyed, antibodies are created, specifically IgE antibodies. The IgE antibodies prepare the immune system for the next encounter with the same allergen. IgE antibodies attach themselves to mast cells. Mast cells are cells that can be found in the respiratory system, gastrointestinal tract, and skin. This process is called sensitization.
If you have been sensitized to urushiol and again come in contact with the sap of poison ivy plants, the urushiol allergen will now be recognized by the antibodies on mast cells. In an attempt to fight off the invaders, mast cells release histamine, which when binding to histamine receptors on skin cells, result in inflammation.
Severe itching and burning will most likely ensue, followed by a blistering rash that may last up to 10 days. Corticosteroid creams can be rubbed into the affected area to lessen the symptoms of the allergic reaction, but this will not shorten the duration of the rash.