The three plants namely poison oak, poison ivy and poison sumac contain an irritating oil sap known as urushiol which leads to an allergic reaction when it gets in touch with the skin and results in the formation of itchy rash that appears in hours of exposure or several days later. One might get directly exposed to urushiol or indirectly through touching objects that have come into contact with the sap of one of the poisonous plant.

The resulting rash is a kind of allergic contact dermatitis. Skin gets sensitized after getting exposed to the substance. When a person gets exposed to urshiol, the skin alerts the immune system regarding the presence of the irritating chemical. At first no visible reaction occurs when a person comes in contact with the plant. When the immune system prepares a defensive reaction for the next time the skin encounters the substance that the skin gets sensitized to the new contact with urushiol which causes an allergic reaction.

Cause

It is caused due to any allergy to resin of the Rhus plant. One is not require to directly come into contact with the roots, leaves or branches in order to get the rash as the plant resins can indirectly reach the skin when one touches the clothing or pet carrying the resin. It can also spread through the air from the pollen. It is an acquired allergy. Some people might not become allergic to Rhus plant whereas many people become allergic to this plant.

Symptoms

The first symptoms of this allergy include redness and extreme itching. The rashes which are caused are in the pattern of streaks or patches consistent with where the plant came in contact with the skin. The rashes which are formed are in the form of papules and might also form large blisters. The rashes generally appear within two days of exposure. They last for one to three weeks.

Treatment

There is no cure for the rashes if they start. One must try and avoid the plant. If contact with the plant has occurred then the oils should be removed from the skin instantly. It has been found that cleaning the affected area with an ordinary soap within 6 hours of the first exposure has been found out to be effective. It has been found out that manganese sulfate solution has been effective in relieving the itch. Cortisone type preparations taken orally have been found out to be effective in treating Rhus rash.