Poison ivy and its pals: some common myths

Poision ivy, poision oak and poison sumac look very different, but they're all part of the same family, and they all cause an allergic reaction for most people

June 26, 2019 

Summer + outside = poison ivy

So, you wore shorts in the woods, and now your skin is itchy, red and swollen. Congratulations, you may have picked up the juice from a member of family Anacardiaceae, which include poison ivy, poison oak and poison sumac.

Mangoes and cashews also belong to this family, which might also explain the rash you got after chewing on a mango rind. According to the American Academy of Dermatology, more than 50 million people a year get a rash from one of these plants, making it more allergenic than all other plants combined. 

Despite that, poison ivy and its pals are often misunderstood. Here’s some common myths about the Anacardiaceae family.

1. The rash is contagious

Nay. Most people catch develop a rash only after contact with the plant’s juices, or urushiol (you-ROO-shee-all), an oily blend of chemicals that the skin absorbs quickly. People with high sensitivity to urushiol might break out from second-hand contact with pets or clothes. But fluids from a weeping rash will not cause the rash to spread elsewhere on the body or to other people. Only contact with urushiol will cause a rash.

2. You can develop an immunity to poison ivy

Not true…So don’t start eating their leaves! There’s very little scientific evidence supporting the idea that people can reduce their sensitivity to poison ivy by increasing exposure. In fact, the more times a person is exposed to poison ivy, the more likely they’ll develop a rash. That’s because the rash is your bodies’ immune system responding to what it perceives as a threat. Once your skin recognizes the poison ivy juice, it will trigger a rash again, sometimes within hours.

There’s some funny irony here. Like other allergens, urushiol isn’t toxic or poisonous on its own. But our immune system doesn’t recognize urushiol, so it attacks the exposed skin.  The closest scientists have come to providing any kind of immunity was in 2016, when researchers isolated the specific protein in our skin that causes that terrible itching. This might lead to better treatment or prevention options. So that’s good news! 

3. “I know I’m immune to poison ivy”

Yes, you could be one of the 10 to 15 percent of the population who tolerate urushiol. But don’t get too excited. You may simply have not encountered it frequently enough to develop an immune response (see above). Evidence also shows that people’s sensitivity to urushiol can change over time. The first time you’re exposed to urushiol it may take several days to get a rash, but if you get it every year, you’ll probably break out within hours.

4. “Leaves of three, let it be”

This is true for poison ivy and poison oak, but not poison sumac (which have between 3 and 15 leaves)  All three can be tricky to identify, because they change colors with the seasons. For poison ivy that means starting in spring with red-tinged leaves, transitioning to a deep green for summer and ending the year with fall colors: yellow, gold and red.

Poison oak and ivy can also take the form of a single plant, a shrub or a thick, hairy vine. No wonder so many of us have trouble avoiding them!

Here’s some pro-tips for avoiding and dealing with poison ivy, sumac and oak rashes:

• Wear long pants when you know you’ll be tromping in the woods. Scrub your skin with soapy water immediately if you know you’ve been exposed. Urushiol absorbs into the skin quickly
• Wash your clothes! Urushiol is very stable and can remain active for years.
• Once you get a rash, there’s a few ways to make yourself more comfortable, including cold washcloths, topical steroids and patience. The rash will likely disappear in less than two weeks.
• If the rash becomes severe, doctors may prescribe oral steroids/p>

Rossie Izlar is a digital producer on the UNC-TV Science team.