Poison Oak: A Guide to Avoiding ‘California’s Most Common Shrub’

Often referred to as “the most common shrub in California,” if you’ve been at all active in the outdoor paradise we call NorCal, you’ve encountered poison oak (PO). Hopefully that interlude was brief and not too unpleasant (ha, ha). The stuff’s absolutely thick in many places, well- known and easily recognized (hopefully) by hikers, fishermen, hunters and outdoor enthusiasts of every stripe. 

The old saying “leaves of three, let it be” remains great advice even today. Along with poison ivy and poison sumac (not found in California), poison oak produces a clear oil compound called Usushiol that easily binds to and is absorbed by human skin. Sensitivity to the rash and itching that follows varies from person to person based on a whole host of circumstances.  

I’ll never forget my first encounter with PO. Our esteemed publisher and his older brother were only toddlers, but managed to bounce the ball they were playing with over our back fence and down the hill behind our house. Of course dad waded through the greenery and fetched the ball, and about a week later found himself in the local emergency room getting cortisone shots. Later, as a long-time NorCal fly fishing guide, I saw it every day and avoided it meticulously, almost as an obsession. Lots of people aren’t so lucky.

So how much do you think you know about this most common shrub? In NorCal it might appear as a tiny bush or a gigantic vine. Sometimes it appears on its own, other times it climbs other bushes or trees. Let’s test your knowledge of our favorite three-leafed little friend.

1: You can get PO from touching objects (like rakes, shovels) that have been in contact with poison oak.

TRUE. According to the Johns Hopkins University web page, the urushiol in poison oak easily adheres to other objects and remains potent for a year or longer. It easily passes from shoes, clothing, pets or smoke from burning PO into the human body.

2: People with light complexions are more susceptible to poison oak. People of color are less susceptible.

FALSE. According to the UNC-TV web page, approximately 10-15 percent of the population are born immune to the effects of urushiol (PO). The rest of us, regardless of skin color, will have a reaction to it. The National Library of Medicine web page describes meeting with a “western Indian chief” where they inquired if the Natives really chewed poison ivy leaves in order to build up immunity. The chief’s response was perfect. “You white men must be crazy,” he said, “to think we would be that foolish.”

3: It would be beneficial for the environment to eradicate poison oak from the wilderness.

FALSE. Lifelong environmental educator and certified arborist Ben Team claims poison oak provides numerous benefits to natural ecosystems. First of all, poison oak appears to have zero negative effects on most animals who browse through it regularly. PO provides habitat for many small animals, lizards, amphibians and insects. Deer, squirrels and other animals consume PO as a major food source. The berries are nutritious food for birds. Poison oak is considered a “pioneer plant,” one of the first to grow back after fires, thereby stabilizing the soil for more complex species like oak trees. The abundance of native PO also keeps invasive species from establishing themselves and having a negative impact on the ecosystem.

4: You can catch PO by coming in contact with someone else’s weeping PO blisters.

FALSE. According to MedicineNet, the only way you can spread PO is by transferring the plant juice (urushiol) to another person. The fluids in PO blisters contain no urushiol.

5: The PO rash is not spread to other parts of the body by scratching.

TRUE. According to the U.S. Food and Drug Administration the only way to spread PO is by coming in contact with the plant oil (urushiol). You may get a rash on your arm one day, and then a few days later the rash erupts on your neck. You assume you touched your arm and then scratched your neck, so the rash spreads. In reality your neck came in contact with the same urushiol your arm did, but the oil is absorbed at different rates by different body parts.

By way of prevention, learn to recognize poison oak in its natural environment and avoid it. It thrives in both wet environments like along lakes and streams, and also in dry, arid chapperels. Anywhere below about 5,000 feet elevation in NorCal is likely ideal habitat for PO. It looks different in different seasons, and you can still get the horrid rash from the bare sticks in the winter time. 

It is possible to thrive in close proximity with “the most common shrub in California.” You need to respect its place in the ecosystem, if only from afar.