Poison sumac is a shrub or small tree that can cause an itchy, painful rash when you touch it. It grows in wet, swampy areas of the eastern United States and is actually more potent than its notorious cousins, poison ivy and poison oak. The plant contains an oil called urushiol that triggers an allergic reaction in many people. Within hours or days of contact, red bumps and blisters can appear on your skin, itching intensely for weeks.

You can identify poison sumac by its leaves, which grow in pairs along a central stem with one leaf at the tip (usually 7 to 13 leaves total). In fall, the leaves turn brilliant shades of orange and red, making the plant beautiful but still dangerous. It also produces small whitish berries that hang in drooping clusters.

The best defense is learning what poison sumac looks like and avoiding it completely. If you brush against it while hiking, wash the area immediately with soap and cool water. The rash itself isn't contagious, meaning you can't spread it to others by touching them, but the oil can linger on clothes, tools, or pet fur and cause new reactions. Even dead poison sumac plants contain the irritating oil, so never burn them. The smoke can cause severe reactions in your lungs and eyes.