Poison oak (Toxicodendron diversilobum and T. pubescens): how to identify it

Poison oak vs true oak, blackberry and poison ivy

The trap with true oak is that a poison oak leaflet can look like a small oak leaf. Look at where the blade joins the twig: a true oak leaf grows singly, while poison oak's grow in sets. The trap with poison ivy is that it is just as hazardous; telling them apart matters less than recognizing both. In the East, Alabama Extension says poison oak's leaflet teeth are more rounded and its leaves often less shiny than poison ivy's.

Why you shouldn't touch it: urushiol

These lines are as the health and extension sources state them. They are not medical advice.

• Every part, every season. The American Academy of Dermatology says these plants are poisonous year-round and that touching any part, including the roots, can cause a rash, even during the winter. NC State says all parts of Atlantic poison oak are poisonous, even when dormant.
• Never burn it. UC IPM says that when poison oak is burned, the oils can disperse via smoke particles, and breathing that smoke can cause severe respiratory irritation. Poison Control says the dead leaves and stems should never be used as kindling, because inhaling the smoke can cause very severe breathing problems.
• It lingers on things. UC IPM says urushiol can persist on tools, clothing, pets and vehicles and stay able to cause a reaction for months or even years. Damage to the plant releases the oil, so weed eating, clearing brush, pruning or trampling are the risky jobs.
• Who reacts. UC IPM estimates that 50% to 75% of adults are sensitive to urushiol. Poison Control says the rash often starts 1 to 2 days after contact, sometimes up to a week, and typically lasts 1 to 2 weeks.

If you touched poison oak: first steps and when to get help

First steps. Poison Control says to rinse your skin with lukewarm, soapy water as soon as possible, then wash, separately, all the clothes you were wearing, along with any tools, backpacks and pets that may have been exposed. UC IPM explains why speed matters: the skin absorbs urushiol quickly, and after 30 minutes the oil has been absorbed. It also says to wash hands and under the fingernails, which spread the oil to other parts of the body, especially the face.

See a doctor, according to Poison Control, if the rash covers a large area or if you can't control the itching. In the US, Poison Control answers at 1-800-222-1222, online or by phone, 24 hours a day.

Pets. UC IPM says a dog's or cat's coat usually protects it from the oil, but the oil on its fur can spread to you; the AAD suggests bathing a pet you suspect has been near these plants, wearing rubber gloves.

Where poison oak grows in the US and Canada

Poison Control sums up the split: poison oak is mainly a plant of the Western states, poison ivy and poison sumac of the Midwest and East. UC IPM gives western poison oak's range as British Columbia to the Baja California peninsula, mainly the western parts of Washington and Oregon, and nearly all of California, where it grows from sea level to about 5,000 feet in coastlands, oak woodlands, rangelands, conifer forests, stream sides, brushlands, parks and gardens. UC IPM calls it the only Toxicodendron species in California.

NC State describes Atlantic poison oak as native to the central and eastern United States, common on North Carolina's coastal plain, and growing in dry, sandy forests and thickets, where it spreads by rhizomes into large colonies.

For a wider view of plants that irritate skin, see plants that cause skin rashes. To keep track of a patch you want to avoid on a trail or in a yard, Plant Identifier's Plant Map records where each located identification was made. If poison oak has to go, ask your county extension office first, wear long sleeves, gloves and long pants, wash everything afterwards, and don't burn it.