Poison Ivy (Toxicodendron radicans or formerly Rhus toxicodendron) is a climbing plant common in eastern and central United States with ternate leaves and greenish flowers followed by white berries; yields an irritating oil that causes a rash on contact. Grows as a vine in the East, Midwest and South, it grows as a vine. In the far Northern and Western United States, Canada and around the Great Lakes, it grows as a shrub. Each leaf has three leaflets.

Poison ivy leaves are coated with a mixture of chemicals called urushiol. When people get urushiol on their skin, it causes an allergic contact dermatitis. This is a T cell-mediated immune response, also called delayed hypersensitivity, in which the body's immune system recognizes as foreign, and attacks, the complex of urushiol-derivatives with skin proteins. The irony is that urushiol, in the absence of the immune attack, would be harmless. The most common treatment for severe contact dermatitis is with corticosteroids, which diminish the immune attack and resulting inflammation. A recent recommendation for mild cases is to use manganese sulfate solution to reduce the itching.

Symptoms from a mild rash can sometimes be relieved by the following:

Cool compresses with water or milk

Calamine - A nonprescription lotion

Aveeno oatmeal bath - A product you put in the bath to relieve itching

Oral antihistamines such as diphenhydramine (Benadryl)

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. During this time, it's important to try to keep from scratching the blisters. Bacteria from under your fingernails can get into the blisters and cause an infection. After about a week, the blisters will start to dry up and the rash will start to go away. In severe cases, where the poison ivy rash covers large parts of the body, it may last much longer.

Although it is often recommended that people learn to recognize the poison ivy plant ("Leaves of three, leave them be"), in practice, this is hard to do, since poison ivy and its relatives are often mixed in with other vegetation and not noticed until after the rash has begun. Keeping the skin covered in situations when exposure is hard to avoid is the best way to prevent the problem.

The clinical name for the skin irritation caused by Poison Ivy is Rhus Dermatitis . It usually starts as itching and small blisters within a few hours after exposure. Depending on how strong the exposure was and/or how sensitive the person is, that may be all there is to it. However, it may develop into an inflamed, swollen rash with open, weeping sores that persists for up to two weeks. Severe cases may require a visit to the doctor. Urushiol is absorbed into the skin within three minutes of exposure. If it is washed off quickly with dishwashing soap and water, the consequences will be less, but you are seldom close to a lavatory when you get exposed, so learning to recognize and avoid it is the best strategy.

Poison ivy rashes typically go away on their own within one to three weeks. In the meantime, you can use self-care methods and over-the-counter medications to relieve signs and symptoms. If the rash is widespread or results in a large number of blisters, your doctor may prescribe a corticosteroid, such as prednisone.

Using a weedeater to remove poison ivy will result in spraying your legs with poison ivy. If you are bare-legged and get scratches while splattered with sap from poison ivy, you may be headed to the emergency room.