Poison Ivy, Oak & Sumac Rash

Poison ivy, poison oak, and poison sumac cause an itchy, often blistering rash called Toxicodendron dermatitis, a type of allergic contact dermatitis. The rash is an allergic reaction to urushiol, a sticky, long-lasting oil found in these plants. About 85 percent of people are allergic to urushiol. The rash usually appears 12 to 72 hours after contact and lasts one to three weeks. At Belaray Dermatology, severe or widespread poison ivy is evaluated and treated at the Hicksville and Stony Brook offices.

What Causes the Poison Ivy Rash?

Poison ivy, oak, and sumac all contain urushiol, an oily resin that triggers an allergic reaction in most people. When urushiol touches the skin, the immune system reacts and produces the red, itchy, blistering rash of allergic contact dermatitis. You can pick up urushiol directly from the plant, or indirectly from anything the oil has touched, such as gardening tools, clothing, shoes, sports equipment, or a pet's fur. Because the oil is invisible and very sticky, it is easy to spread to other parts of the body before you realize you have touched it.

What the Rash Looks Like

The rash is intensely itchy and usually shows up as red streaks or patches where the plant brushed against the skin, often in straight lines. Small bumps develop into blisters that may ooze and then crust over. On thinner skin the rash appears sooner, and on thicker skin it can take longer, which is why the rash often seems to appear in stages over several days.

Facts vs. Myths

Poison ivy is surrounded by myths that cause needless worry. Here is what is actually true.

• Myth: The rash spreads when you scratch it or when the blisters break. The fluid inside the blisters does not contain urushiol and does not spread the rash. New patches that appear over a few days come from areas that received less oil or have thicker skin, or from urushiol still on unwashed skin, clothing, or objects.
• Myth: You can catch poison ivy from another person. The rash itself is not contagious. Only the urushiol oil transfers, so you would have to touch oil that is still on someone's skin, clothing, or pet.
• Myth: Dead or dried-out plants are safe to handle. Urushiol stays active for months to years, even on dead plants and on old clothing, shoes, or tools.
• Myth: If you have never reacted, you are immune for life. Sensitivity can develop at any time after repeated exposure, so a first reaction can happen at any age.
• Myth: Burning the plants is a good way to get rid of them. Never burn poison ivy, oak, or sumac. Urushiol travels in the smoke and can cause a severe rash on exposed skin and a dangerous reaction in the lungs if it is inhaled.

What to Do Right After Contact

Acting quickly can prevent or reduce the rash.

• Wash the skin with soap and cool water as soon as possible, ideally within about 10 minutes. A dedicated poison-ivy wash (for example Tecnu or Zanfel) can also help, but plain soap and water works if you act fast.
• Scrub under the fingernails, where oil often hides and gets spread to the face and eyes.
• Wash contaminated clothing, shoes, and tools separately in hot water, and wipe down anything else the oil may have touched, including pets.
• Avoid touching your face and eyes until you have washed your hands thoroughly.

How to Treat the Rash

Once the rash appears, treatment focuses on calming the itch and protecting the skin while it heals.

• Apply cool, wet compresses, calamine lotion, or a colloidal oatmeal bath to soothe itching.
• Use an over-the-counter 1% hydrocortisone cream on mild rashes.
• An oral antihistamine at night can help you sleep through the itch.
• Keep fingernails short and try not to scratch, which can break the skin and lead to infection.

When to See a Dermatologist

See a dermatologist promptly if the rash is on your face, eyes, mouth, or genitals, covers a large part of the body, causes severe swelling, involves many blisters, or is not improving after a week or two. Poison ivy is a form of contact dermatitis, and if you get rashes often without a clear cause, ask about contact dermatitis and patch testing. Belaray offers same-week evaluation and prescription treatment at its Hicksville (Nassau County) and Stony Brook (Suffolk County) offices.

How to Prevent Poison Ivy

• Learn to recognize the plants. Poison ivy and poison oak usually grow in clusters of three leaflets, so the saying is “leaves of three, let it be.” Poison sumac has 7 to 13 leaflets on each stem.
• Identify it in winter or when there are no leaves. A mature poison ivy vine climbing a tree is covered in thick, reddish-brown aerial roots that give it a fuzzy, hairy, rope-like look, which is why gardeners say “hairy vine, no friend of mine.” Clusters of small, waxy, white or cream-colored berries can also linger into fall and winter. The bare vine and roots still contain urushiol, so treat any hairy vine as poison ivy and do not touch it.
• Wear long sleeves, long pants, gloves, and closed shoes when hiking, gardening, or clearing brush.
• A barrier lotion containing bentoquatam, applied before exposure, can reduce how much urushiol reaches the skin.
• Wash your skin, clothing, tools, and pets after possible contact, and never burn the plants to remove them.

Frequently Asked Questions

How long does a poison ivy rash last?

A poison ivy rash usually appears 12 to 72 hours after contact with the plant's oil and lasts about one to three weeks. Milder cases fade on their own with home care, while severe or widespread rashes clear faster with a prescription steroid from a dermatologist.

Is poison ivy contagious? Can it spread to other people?

No. The rash itself is not contagious, and the fluid in the blisters does not spread it. Poison ivy only spreads through urushiol, the plant's oil, so you would have to touch oil that is still on someone's skin, clothing, tools, or pet.

Why does my poison ivy rash keep spreading?

It usually is not truly spreading. New patches over several days come from areas that got less oil or have thicker skin, or from urushiol still on unwashed skin, clothes, or objects. Washing everything the oil touched, and yourself, stops new spots from appearing.

What dries up poison ivy the fastest?

The single most important step is washing the urushiol off with soap and water as soon as possible, ideally within about 10 minutes. For the rash itself, cool compresses, calamine lotion, colloidal oatmeal baths, and over-the-counter hydrocortisone help. Severe cases resolve fastest with a prescription steroid from a dermatologist.

Can you be immune to poison ivy?

About 15 percent of people do not react to urushiol, but sensitivity can develop at any point after repeated exposure. Never assume you are immune, because a first reaction can happen at any age, even if you have handled the plants before without a rash.

When should I see a dermatologist for poison ivy?

See a dermatologist if the rash is on your face, eyes, mouth, or genitals, covers a large area, causes severe swelling, shows signs of infection, or is not improving. Belaray Dermatology offers same-week evaluation and prescription treatment at its Hicksville and Stony Brook offices.

Related reading: contact dermatitis and patch testing, eczema in children, and our recommended over-the-counter products.