Poisonous Plants

Poison ivy, poison oak and poison sumac are the most common poisonous plants. They all produce urushiol, an oil that triggers an allergic reaction in almost everyone. Simply touching these plants is enough to cause an itchy, annoying skin rash. You can also develop a rash if you touch an object or clothing that has touched the plants’ oil. This rash is a type of contact dermatitis.

Almost everyone is allergic to poisonous plants. Nearly 90 percent of people who touch urushiol develop an itchy skin rash. It only takes a small amount — 50 micrograms (about the size of a grain of salt) — to prompt an allergic reaction. However, your vulnerability to urushiol changes over time. Even if you’ve never developed a rash from touching a poisonous plant before, you can still have a reaction later in life.

Sensitivity to urushiol also varies by person. Some people are more likely to have an immune response after exposure to the oil. Roughly 25 percent of people don’t have an allergic reaction to urushiol. But up to 25 percent of people have a severe immune response.

It’s a common misconception that you can develop a rash by touching the rash of someone who has touched a poisonous plant. Fluid from blisters doesn’t contain urushiol, so it isn’t contagious. However, you can break out in a rash if you touch lingering urushiol on their body, clothes or any other contaminated objects.

These poisonous plants exist everywhere in the mainland United States. Knowing what they look like can help you avoid contact.

• Poison ivy. Poison ivy grows as a shrub in the Western United States or as a vine in the eastern part of the country. Shrubs may have white berries. The leaves have three leaflets, and they change color during the year. Leaves are reddish in spring, green in summer and yellow, orange or red in fall.
• Poison oak. Poison oak grows as a shrub (sometimes with white or yellow berries) in the Eastern and Southern United States. It’s a vine in the western regions. Like poison ivy, its leaves have three leaflets, but poison oak leaves have rounded tips. The bottoms of the leaves are fuzzy and lighter in color.
• Poison sumac. Poison sumac trees grow as tall as 20 feet. Their leaves contain groups of seven to 13 smooth leaflets that grow in pairs. These clusters often have cream-colored, green or pale-yellow berries. These trees grow in wet, marshy areas in the Northwest, Midwest and Southeast United States.

Rashes caused by poison ivy, poison oak and poison sumac look the same. The most common reaction is a breakout of red, itchy bumps. However, some people may experience black spots or streaks with minor swelling or redness. This type of allergic response is rare.

Depending on how sensitive your skin is, your rash may appear within a few hours to a few days after you touch urushiol. Your rash may appear in one or two places where you touch urushiol, or it may cover your entire body in severe cases. Once you break out, the most common symptoms include:

• Blisters
• Itchy skin rash
• Redness
• Swelling

You may also have difficulty breathing if you’ve burned poisonous plant leaves and inhaled the smoke. Once your rash appears, it will likely last up to 14 days. Some rashes last as long as 21 days. During this time, your rash will develop in stages:

• Itching. You will feel intense itching where the poisonous plant touched your skin.
• Rash. A rash quickly appears after you start to itch. Most people develop an intense rash with blisters.
• Blisters. Blisters that appear will eventually burst open and leak fluid.
• Crusting with more itching. Blisters begin to dry and crust over. You will still feel itchy.

Our providers can usually diagnose your poisonous plant rash by looking at it. They will ask several questions about your activities to determine if you’ve been exposed to these plants. If you haven’t been outside in areas where poisonous plants may be, they will evaluate you further to identify the cause of your rash.

Poisonous plant rashes usually heal on their own within a couple of weeks. Our providers recommend these over-the-counter treatments to help manage and relieve your symptoms while you wait to heal:

• Anti-itch cream. Hydrocortisone creams and calamine lotion can reduce your itching. Once your blisters burst and start to drain, you can switch to topical solutions made with aluminum acetate.
• Antihistamines. Oral medications can relieve itching. Do not use topical antihistamines. They can make your rash and itching worse.

If your poisonous plant rash is severe or has spread across your body, our provider may prescribe an oral steroid like prednisone.

These at-home remedies can also relieve your symptoms:

• Cold compresses. Place a cold, wet (wrung-out) washcloth over your itchy skin to relieve the itchiness.
• Lukewarm bath. Take short, lukewarm baths with either colloidal oatmeal or 1 cup of baking soda. If you prefer showers, keep them short and cool.

These self-care behaviors will also help your rash heal faster:

• Wash everything. Wash your body with warm, soapy water to remove all urushiol. You should also wash whatever you were wearing because urushiol can stick to clothes. Take the time to clean anything else that touched the poisonous plant (gardening tools, camping gear, pets, etc.)
• Don’t scratch. It may be hard to resist scratching but try not to. If you scratch too hard and break the skin, you could get an infection.
• Leave blisters alone. Don’t touch or pick at your blisters. The overlying skin of your blisters protects the skin underneath and prevents infection.
• Keep skin clean and dry. These steps can help prevent infection.

Remembering what poisonous plants look like and avoiding them is the best way to prevent a rash. But these additional steps may also help you prevent a breakout:

• Remove or kill the plants. If you identify poison ivy, poison oak or poison sumac in your yard, spray an herbicide or pull them up. Wear gloves and be sure to remove the roots of the plants. Do not burn the plants (smoke can carry urushiol). Throw the gloves away and wash your hands.
• Wash your skin or your pet. Wash your skin and scrub under your fingernails within 30 minutes of urushiol exposure. If you think your pet was exposed, wash them thoroughly while wearing long rubber gloves.
• Wear protective clothing. If you think you’ll be near poisonous plants, wear long pants, long sleeves, gloves, socks and closed-toed shoes.

For most people, poisonous plants only cause an itchy rash. However, you should seek immediate medical attention if you have difficulty breathing after inhaling smoke from poisonous plant leaves.

You should also see a healthcare provider if your:

• Blisters ooze puss
• Fever rises over 100°F
• Rash affects your eyes, genitals or mouth
• Rash doesn’t improve within a few weeks
• Rash is severe and widespread
• Skin continues to swell