Poison Oak: "Leaves of three; leave them be" by David Robles, MD, PhD

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Poison oak is a weed that has three leaflets per leaf. It belongs to the genus Toxicodendron—which includes poison oak, poison ivy, and poison sumac. Together, they cause more allergic contact dermatitis than all other plant families combined. The old adage “leaves of three; leave them be," refers to each leaf having three leaflets. 

"Leaves of three; 
leave them be"

 Poison oak grows mostly in the Western United States as a shrub. The leaves, roots, or twigs contain the oils (resin), which is capable of causing dermatitis. The rash is very itchy and is characterized by itching, redness, and even blister formation. The dermatitis usually first appears in sensitized individuals within 1-3 days after contact. The rash does not spread by the fluid from the blisters. The reaction can vary from mild to severe and in rare cases, may require hospitalization. 




If you live in the Western North America (from British Columbia down to the Baja California Peninsula) you should familiarize yourself with this plant so you will be able to recognize it on the trails. 
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