1. Poison ivy grows throughout North America in wooded areas, especially near the outskirts, and is sometimes found on exposed rock and as underbrush in open fields. It can be a shrub-like cluster or a vine crawling up other plants. Identify it by its cluster of three leaves with reddish hairs on the vine. It has no thorns.
2. Poison oak is an upright shrub that grows in thickets and forests along the western coast. Like poison ivy, its leaves grow in groups of three but with scalloped edges (resembling the leaves of an oak tree, hence the name). The leaves range in color from reddish to bright green, depending on the time of year.
3. Poison sumac grows in wet, swampy areas, commonly in the southern and eastern US and Canada. Unlike poison ivy and poison oak, it's a small tree or large shrub, and instead of growing in groups of three, its branches grow between 7 and 13 leaves. The leaves are oblong, tapering to a sharp point. You can identify the poison variety of sumac by its drooping green berries while harmless regular sumac has bright red, upright clusters of berries.
The skin reaction is not to the plants themselves, but to their toxic sap called urushiol. It's found in all parts of the plant, not just the leaves (a common myth). Also keep in mind that any exposure to urushiol will cause a reaction, even if it's indirect contact with gardening tools or clothing.
If you can treat the exposed area soon enough, you may be able to avoid or lessen the reaction. Rinse well with water only (soap can spread the sap), then use antihistamines and hydrocortizone creams to alleviate the symptoms. Soaking in a cool oatmeal or baking soda bath can also help soothe the itching.
If you've ever been sidelined by these nasty plants, you know it's well worth the extra diligence to avoid them when gardening, hiking or camping this summer. Check the photos and save your sanity!