Well over half of the human population is sensitive to poison ivy, poison oak or poison sumac. Rashes usually peak in early summer, and tens of thousands of people in the United States go to the emergency room every year as a result. Even if you’ve gone your whole life without a sensitivity, you can develop an allergy at any point.
Your best bet for staying rash-free is leaving plant life alone. But when you can’t avoid it, it’s helpful to know the characteristics of poison oak and ivy. A good rule of thumb is “leaves of three, let it be.” Leaf shape, size and color are less helpful, since they are notoriously varied in these plants. Another important tip: The entire plant, from root to leaf, contains the allergenic oil urushiol.
Ready to test your knowledge?
That’s poison ivy. Poison ivy and oak leaves almost always grow in threes, shaped like a lowercase “t” with two leaves (technically called leaflets) on the sides and one at the end with a slightly longer stem.
Fun fact: The allergenic oil is on only the inside of the plant, not the outside, according to John Jelesko, a botanist at Virginia Tech. But best not to press your luck.
That’s poison oak. Like poison ivy, it has three leaves, one with a longer top stem: Are you getting the hang of it? This is a pretty classic leaf for poison oak: small, lobed and a little waxy. But just note that these are not always reliable identifiers. Poison oak leaves that grow in the shade, for example, can be almost the size of your hand and not shiny at all.
That’s Boston ivy. Although it has three points, they are all part of a single leaf.
There is plenty of anecdotal evidence that urushiol can stay active on clothes and objects for perhaps a year, though this hasn’t been well studied. Your safest bet is to clean the tools with soap and wash any clothes that might have oils on them.
Poison ivy, like many plants, changes colors in the fall. And it can give you a rash year round, though there is less oil in dead leaves. Poison oak can change colors even sooner, as early as July in a dry year, said Barb Lachenbruch, a professor emeritus of forest biology at Oregon State University.
That’s wild sarsaparilla. Though it’s sometimes confused with poison ivy, it’s totally safe to touch and actually makes a tasty drink similar to root beer.
Tricky one. That’s poison oak growing up a Douglas fir tree. Poison oak can look like a vine or a shrub or both, but it will always have the leaves of three.
Those are wild strawberries, and they’re totally safe to touch! Yes, they have three leaves. But remember that on poison oak and poison ivy, the top leaf will always have a longer stem.
The fuzzy vine is a big hint, though other plants’ vines can look similar. This particular one is poison ivy, and it can still give you a rash if you touch it in the winter, even if it has no leaves.
Remember it this way: Hairy vine, no friend of mine. If you want to remove it, be sure to wear protection and be ready to work hard. Poison ivy is notoriously stubborn, and a large vine might require a crowbar to loosen.
If you washed her with something like dish soap, she should be fine for cuddles! Dogs are highly unlikely to get a rash themselves but can carry urushiol on their fur, perhaps for days, and spread it to us.
Fun fact: Humans are the only North American species that easily gets a rash from poison ivy. Many animals, like deer, rabbits and bears, actually enjoy eating poison ivy, oak and sumac. And poison ivy berries are a crucial winter food source for dozens of bird species.
While we generally think of poison ivy preferring backyards or forest edges, the plant is surprisingly adaptable and can even live along the beach. Note: Sunburns and rashes do not pair well.
This is Virginia creeper, one of the plants most commonly confused with poison ivy, according to Shelley Mitchell, the education director of the Botanic Garden at Oklahoma State University. It’s certainly safe to touch. Look closely and you can see it has five leaves, not three. Think of it like a hand waiving hi, Dr. Mitchell said, whereas poison ivy is like a hand raising a middle finger.
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