Hikers, beware: The atmospheric rivers that drenched California this winter have produced what the California Poison Control System is calling a “bumper crop’ of poison oak that’s flourishing in grassy hillsides, forests, recreation areas, and coastal locations.

The CPCS says the plant is a serious threat, especially to those who are allergic to it.

It’s identifiable not only for its leaf structure — as the hikers’ saying goes, “leaves of 3, let it be” — but also for its climbing, vinelike appearance. The University of California Agriculture and Natural Resources in Davis says it forms a dense, leafy shrub that can stand as tall as 6 feet high, with either glossy or dull leaves. The stalk of the central leaflet in the three-leaf cluster is longer than the other two.

Dr. Rais Vorha, medical director for the Fresno/Madera division of the CPCS, says that you can be contaminated by poison oak not only by touching the plant directly but also by touching clothing, shoes, gloves, pets, and tools that have come in contact with the plant.

“Even smoke from burning plants can cause irritation,” he said.

Exposure in allergic individuals can result in a rash erupting one to six days after exposure that will itch and form water blisters.

Poison Oak Tips

• Wear boots, gloves, and long pants when hiking.
• Stay on trails away from brush where poison oak grows.
• If you are exposed, wash the area thoroughly with lukewarm water and apply rubbing alcohol, which may wash away the plant’s oil.
• Wash all clothing, tools, and pets that have been exposed.
• Calamine lotion or hydrocortisone cream and antihistamines can help stop itching.
• Do not scratch the rash because that can lead to infection.
• Seek immediate medical help if you have trouble breathing or swallowing, the rash covers much of your body, you have many blisters, or swelling occurs, especially in the eyelids, face, or genitals.

For more information, visit the CPCS poison oak website or call Poison Control at 1-800-222-1222.