Know the Difference: Poison Ivy, Poison Oak and Poison Sumac

While summer officially ends in September, there are plenty of people who enjoy camping, hiking and other outdoor activities well into the fall. Coming into contact with poison ivy, poison oak, or poison sumac, however, can put a damper on all of the fun.

It might be hard to avoid these poisonous plants altogether, but it’s a good idea to learn a few key ways to identify them, limit your exposure, and apply effective treatment.

How can you tell poisonous plants apart?

Most of us have heard the expression: “Leaves of three, let it be.” That’s good advice when it comes to poisonous plants, but what do poison ivy, sumac, and oak actually look like, and can you always trust that adage?

Poison ivy, oak, or sumac may display subtle differences, depending on the season or location in which they’re growing. But they all have small white, tan, green, yellow, or cream-colored berries in the autumn months. That alone can be helpful in differentiating them from other similar, but harmless plants. Here are a few additional tips for telling them apart:

Poison Ivy

Poison ivy has leaves of three, though it has been known to sometimes have more. Its leaves are broad and spoon-shaped, appearing reddish-colored in the spring, green during the summer months, and bright red, orange or yellow in the fall. It can grow as a climbing vine, one that spreads through grass, or even as a shrub.

Poison Oak

Poison oak is rarely found in Wisconsin, but it’s not impossible to find it here. Its leaves closely resemble oak leaves. While it usually has three leaflets, it can have as many as seven in each grouping. Leaves also have deep tooth-like edges around the perimeter.

Poison Sumac

Poison sumac, while not nearly as common as poison ivy or poison oak, is mostly found in wet, wooded areas of Wisconsin. Each leaf stem contains seven to 13 leaflets and features smooth edges and pointy tips. The leaves grow in pairs opposite one another on the leaf stem. It typically grows as a shrub or small tree.

How can I protect myself against poisonous plants?

“Your best defense is knowing how to spot each plant before you come into contact with it,” said Dr. Zachary Baeseman, Family Medicine Physician and Associate Medical Director at ThedaCare. “If you’re not sure whether something is poisonous, but it has three leaves, err on the side of caution.”

Your best defense is knowing how to spot each plant before you come into contact with it.

Zachary Baeseman, MD, ThedaCare

Other tips for prevention include:

• Applying a barrier cream to your skin before you go out into the woods
• Wearing long sleeves and pants (doubles as protection against tick-borne illnesses)
• Staying on established walking or hiking trails
• Washing well with soap and water once you return home
• Bathing your dog with a good pet shampoo if you have a concern your pet has come into contact with a poisonous plant (remember to wear rubber gloves)

If any poisonous plants have invaded your yard, wash your garden tools and gloves regularly. If you’re trying to remove the plants from your yard or working around them, wear long sleeves and pants tucked into boots. It’s also a good idea to wear impermeable gloves.

What symptoms result from contact with a poisonous plant?

“They all have a similar mechanism for causing rashes,” Dr. Baeseman says. “Each plant transfers a resinous sap material that causes irritation and produces a rash. The rash typically resembles a straight line of redness and may include some fluid-filled blisters. With significant exposure, the area of redness can be more widespread.”

If you have difficulty breathing or swallowing, or your face is swelling after
encountering a poisonous plant, CALL 911.

Keep in mind, a rash from poison ivy or other poisonous plants cannot be spread from person to person, even through fluid-filled blisters. Refrain from scratching blisters, as dirt from under your fingernails could cause an infection and add to your discomfort.

One note — if you develop a painful rash that has blisters, you may have shingles.

“Shingles has a few characteristics that make it very distinguishable from poison ivy, but it may not be obvious if your rash is small or if it’s located in a small area,” Dr. Baeseman says. “If you’re in doubt, you should send your provider a picture, schedule a virtual visit, or make an appointment for an in-person examination.”

What is the best course of treatment?

Applying a wet compress or soaking the affected area in cool water can help relieve the itching. Some over-the-counter products can provide relief, such as antihistamines or hydrocortisone cream. For severe cases, your doctor can prescribe a topical steroid or oral corticosteroid.

If you’ve encountered a poisonous plant, it’s critical to remove your clothes as soon as possible and wash them with detergent.

“Most basic laundry detergents are going to be adequate enough to remove the poisonous substance from your clothing, but you should do it right away,” Dr. Baeseman says.  

When do I need to see a doctor?

Rashes from poisonous plants will often clear up on their own with minimal care or treatment. However, you should see your doctor if you experience any of the following:

• A temperature over 100 degrees Fahrenheit
• Pus or soft yellow scabs, or tenderness on the rash
• Itching that worsens or keeps you awake at night
• A rash that doen’t improve within two or three weeks; spreads to your eyes, mouth, genital area; or covers more than one-fourth of your skin

A growing threat: wild parsnip

While poison ivy, oak and sumac are important to watch out for, Dr. Baeseman warns the increasing presence of wild parsnip in our region also warrants concern.

“Wild parsnip and a variety of plants in the same category, such as hogweed, wild celery, or wild carrot, have a different mechanism of action,” Dr. Baeseman says. “Generally speaking, it’s not a resinous sap; it’s actually a UV reaction with the sun following contact with the plant that causes a problem.”

Over the course of the past decade, wild parsnip has become a well-known invasive species in Wisconsin, spreading to more than half of its counties.

“Unfortunately, any wooded area could contain wild parsnip,” Dr. Baeseman says. “Fields — including cornfields — are also a common breeding ground for hogweed, wild parsnip, and wild carrot, all of which could result in potentially lethal third-degree burns,” Dr. Baeseman says.

Fields — including cornfields — are also a common breeding ground for hogweed, wild parsnip, and wild carrot.

Zachary Baeseman, MD, ThedaCare

Unlike the itchy reaction to poison ivy, oak, or sumac, people exposed to wild parsnip and the like will experience more of a burning feeling. The best course of action upon coming into contact with such plants is to avoid sunlight and to shower immediately afterward.

“There are several plants that can produce painful and irritating results following contact,” Dr. Baeseman says. “But this shouldn’t stop you from exploring the great outdoors. Familiarize yourself with each plant’s most common traits, learn where they are most prominent, and be vigilant about your surroundings. Wearing appropriate clothing and practicing good hygiene are also important. Awareness is everything.”