But poison oak may have more than three leaves, and depending on the season, species and local environment, plants can vary. All parts of the plant, including roots, can cause an allergic reaction ...

Poison ivy, poison oak, and poison sumac are three plants notorious for causing itchy, uncomfortable rashes that can turn a pleasant outdoor experience into a nightmare.

Here's what you need to know about some of the more common plants to avoid, like poison hemlock, poison ivy and poison oak.