The Poison Plants of Summer: Poison Ivy, Oak and Sumac

Summer is in full swing. You know the signs. Mom fires up the grill, Dad finds his green thumb, your kids fetch a ball in the weeds… and the whole family comes down with an itchy rash. That’s right, the poison plants are back, and this summer, they promise to send 40 million Americans to seek medical care.

Poison Ivy, Oak and Sumac

These three plants are native to America and surprised early European explorers. Captain John Smith wrote, “The poisoned weed is much in shape like our English ivy, but being touched, causeth redness, itching, and lastly, blisters.”

Today, we know these plants cause a type of allergic dermatitis. Upon exposure, the immune system revs up, attacking the plant oil and damaging the skin. The few who don’t react should still watch out because an allergy can develop anytime, even when previous exposure did not cause a problem.

The offending oil is urushiol (oo-ROO-shee-awl), a yellowish substance inside the plant’s leaves, stems, and roots. Because the oil is inside, undisturbed leaves won’t harm you. However, if the plants become dry, insect-chewed, or otherwise damaged, the oil leaks to the surface, where it comes into contact with humans and other animals.

As it turns out, only primates are allergic. Dogs, cats, cattle, and sheep don’t break out but can pass the oil to their human keepers. Clothing and tools also spread the oil, and since urushiol remains active for years, unsuspecting spring gardeners can get a rash from last season’s gloves and tools.

Treating the Rash

If you come into contact with one of these plants, you should wash immediately with soap and water. Unfortunately, this won’t always prevent the rash because the oil bonds fast to human skin and is nearly impossible to remove within 30 minutes of exposure. This also means you will not spread the rash by touching the affected skin. The rash may have the illusion of spreading, but this is because areas with the greatest exposure and thinner skin tend to break out first.

Once you have the rash, it typically lasts 2 to 3 weeks as the damaged skin is replaced with new skin. All you can do is treat the symptoms and prevent infection. For mild cases, over-the-counter hydrocortisone cream and oral antihistamines—like cetirizine—work well to control inflammation and itching. Topical antibiotic ointment may prevent bacterial infection when the skin is broken open from repeated scratching. If you have a widespread rash, face or genital involvement, or signs of infected skin, it’s time to see your doctor. In these cases, prescription steroids or antibiotics might be necessary.

Preventing the Rash

Prevention by avoidance is best. All three plants have compound leaves, most commonly with three leaflets. My Grandma Bert used to say, “Leaves of three, let them be!” and she was right. The leaves are smooth and glossy, colored with a summer green that transitions to autumn shades of orange and scarlet. Poison ivy is a stout, weedy vine that climbs trees east of the Rocky Mountains. Poison oak is larger, shrub-like, and found west of the Rockies. Poison sumac grows in swampy areas of the Southeastern United States, where it can reach heights of twenty feet.

Medications containing the chemical bentoquatam (BEN-toe-kwa-tam) prevent the rash by providing a barrier on the surface of exposed skin. It is available over the counter and approved for ages 6 and up. To remain effective, it should be applied at least 15 minutes prior to expected exposure and reapplied every 4 hours.

Poison Hemlock

This one is different than the first three, but still an important plant to recognize and avoid. Poison Hemlock is not native to America—settlers brought it from Europe as an ornamental garden plant. Today, it grows in nearly every state (including Ohio). Poison hemlock does not contain urushiol, so you won’t get a long-lasting rash from brushing against the leaves. However, the plant contains poisons known as alkaloids inside the seeds, roots, stems, and leaves. Alkaloids interfere with the body’s ability to send messages through the nervous system. This can result in vomiting, seizures, difficulty breathing, confusion, and death. And since poison hemlock resembles wild carrots, parsnip and parsley, many people eat it by mistake and end up in an emergency room. Touching the plant can also be dangerous because the alkaloids can enter your bloodstream through small scratches in the skin.

So, get out there and enjoy your summer. Fire up the grill. Tend the garden. Play ball. But don’t forget to freshen up your plant identification skills and steer away from the poison plants of summer. Otherwise, you might find yourself seeking medical care for itchy skin… or worse!