You can look, but you better not touch...The Coasters, 1959
A look at natural history, some human biology, preventive measures, and myths.
Three-leafed, poison oak foliage poking through the ferns in late February. It was nearly invisible the week before! The young leaves flash a shiny, copper color that later turns green.
Hikes in our favorite Park prominently feature beautiful plants...towering redwoods, ramrod firs, courageous tan oaks, stalwart live oaks, and kinky madrones in the glades...and alders and big leaf maples overhanging the creek. Ferns, mushrooms, mosses, and horsetails take us to Paleozoic times...and back again. Springtime delivers waves of flowers...trillium, houndstooth, poppies, lupines, phlox, and more.
Springtime also brings us close to a scourge of the coastal woods: Poison Oak... (Toxicodendron diversilobum). For that matter, summer, fall, and winter do, too.
Poison oak is definitely a native plant, so we’ll make no disparaging comments about invasive species! It’s all ours.
The leaves of poison oak come in threes, just like poison ivy. The poison oak leaves have a subtly bumpy edge, reminding some of lobulated white oak leaves, whereas the ivy has smooth edges. The juice of either one is trouble on your skin.
How does it work?
The Coasters again: “Poison Ivy, Lord, will make you itch.”
“Poison” is a loaded word. We think of certain mushrooms, foxglove (digitalis), hemlock, and other plants that make a person sick (or worse) after eating them. We won’t be eating any poison oak, but this plant gets you through the skin.
Poison oak and its Eastern relative, Poison Ivy, and Poison Sumac share an oily resin in the leaves, stems, and sap. This substance, urushiol, is a powerful skin sensitizer, meaning it binds to proteins in the skin. The human immune system identifies this hybrid material as “foreign.” In an effort to defend the host, the immune system launches specialized cells to attack the “invader.” That allergic response inflames the skin as collateral damage.
After a first exposure or two, a person may not notice much, but harm waits in the wings. Subsequent exposures can result in an intensely itchy, bumpy, blistery rash that can range from a nuisance to a condition that can ruin a couple weeks. Unpleasant drugs usually come into play in the bad cases. The severity of the reaction seems to get worse with each new exposure...as well as after a heftier dose of the resin.
Web images of bumpy red stage and blisters
Adult hikers who were explorative kids once upon a time probably have been exposed...and the allergy persists a lifetime. The worst cases I saw in my practice were adolescent boys horsing around among the bare twigs in the ravines all day in late winter...before the shiny leaves sprouted. (They’re all grown up now, but their allergy endures.)
Brushing against the leaves is obviously a bad idea, but exposures to the naked stalks and roots can do the same. This resin is quite durable. If you come back from a hike with this resin on your shoes, laces, socks, or pants, you’ll get it on your hands when you change your clothes. Then you rub your eyes...Uh oh! If you handle those clothes a month later without washing them, the resin will still be there, and you may dose yourself again.
If your puppy dashes off the trail into the brush, Fido may come back to you with an invisible gloss of urushiol on his fur. (Your Park-compliant dog leash can get resin-ated, too!)
Mountain bikers on overgrown trails may accumulate oodles of resin on their garments and equipment. It leaves a mark....
Eventually, the skin replaces damaged and inflamed cells. The allergy afflicted skin dries out and peels away, but that often takes 2 weeks or a little more.
It’s a Sneaky Plant!
Poison oak can grow into impenetrable thatches like this one...but it can also be sneaky!
Here’s an enterprising poison oak plant creeping over the back of a park bench on the Seacliff Beach stairs in early April. It grew 2-3 inches a day!
Propagation
Poison oak is “committed to the future.” It sends root runners 30 feet or more to push up new resin-dispatching foliage. It makes demure blossoms which become berries which birds will pluck up and deposit far away. It happily grows 2 stories up a tree and scatters seeds in the wind. A cut twig on moist ground will push roots into the soil and set up housekeeping. It is not...ever...going away.
Keep our Tectonic Plates Close!
Some of us quip that the only reason the San Andreas Fault hasn’t cleaved off the coast of California like Madagascar or Baja California is that the roots of poison oak have securely stitched the North American Plate to the Pacific Plate.
The sheer density of this winter dormant patch of poison oak from the highlands of Big Sur suggests that plate suturing might not be a totally preposterous theory. (OK, that’s just a joke.)
Some Easterners deprecate California’s fall colors. They’re possibly opinionated, but they have probably missed the crimson autumnal splendor of our poison oak.
Practical Prevention
Statistically, about 15% of people seem not to develop an allergy to poison oak resin even if exposed repeatedly. That’s a great blessing! I’m jealous. That leaves 85% who will. People who haven’t yet suffered, and who act foolishly in the underbrush thinking they are exempt, often learn the hard way they’re among the 85 percenters destined to itch like crazy.
Time is important. The resin binds to your skin proteins rather quickly, within an hour or two, and then it won’t wash off. The deed is done.
Once you break out with itchy red bumps, usually a day or two later...it’s too late. It’s gotcha, and it usually gets worse before it dries up. Better to think ahead than play catch-up!
Stay on the trails and avoid the brush. State Parks, with the Advocates’ Volunteer support, does a diligent job of clearing overhanging brush...but there are 40 miles of trails. An ambitious poison oak plant can send a juicy, drooping, head high shoot over a trail in a mere week in April, especially after a wet winter!
If you do plan to venture off trail into greenery, wear long pants, consider wearing gloves, and assume that you’ll come out with some resin on your clothes. Throw those clothes in the washer with strong detergent when you get home, and wash your hands with strong soap as soon as possible. Try not to fiddle with your face (or other tender parts) in the meantime!
Remember that after the leaves fall in autumn, those coffee-and-cream colored twigs are still happy to share resin with you. Leaves don’t pop out until February...later at altitude.
If you have a furry pet that snuffles around in the brush, it’s time for a serious shampoo when you get home. Assume you’ll have resin on your hands, and wash with strong soap.
Bikers moving through overhanging vegetation below 5000’ elevation are going to get dosed. There are commercial products which claim to shield the skin from the resin. Every bike store carries them, and the web is full of bold claims. Regard those nostrums as “possibly helpful,” but NOT a substitute for prudence. Meanwhile, those garments need washing after a ride, and the bike needs a bath, too, with serious soap. (e.g. Simple Green.)
Teach school aged children to recognize the three-leafed plants when they are just sprouting, later when they are green and leafy, and when they turn red in the fall. Dress kids to cover exposed skin if feasible, and make bathing a ritual when you return home.
Splendor in the Grass was a suggestive movie in the early 1960’s. Splendor in the Brush in coastal California...not too wise.
Let’s De-bunk Some Myths
Poison Oak can get you just by being close. Not true, thankfully. The resin is thick and sticky, and it doesn’t spontaneously waft through the air from the verge of a trail. Exposure requires physical contact with the leaves, stems, roots...flowers and berries, too.
Weed whacking poison oak generates a spatter of juicy leaf fragments that will contaminate exposed skin and everything you wear. Just Don’t Do It. Hire a goat.
Now, this is rough. Agricultural and other brush clearing burns can volatilize the urushiol resin into the plume of smoke, and the inhalation can cause lung problems. This can be a serious problem for fire fighters in the foothills.
Poison Oak is contagious. That’s also not true. Once the resin has bonded with your skin, which happens in about an hour or so, you can’t wash it off. It’s molecularly stuck to you. The itchy red bumps appearing a day or two later are a sign your immune cells are doing battle underneath...but the free resin is no longer loose on the skin. If the rash develops blisters, which it commonly does, the blister fluid does not contain urushiol, and it won’t spread to another area of the body or another person. (Lots of bogus info about that out there.)
However, people with fresh resin on their fingers or their clothes can share that with acquaintances...or eyes, or private spots.
Remember the doggie. Wash your hands, socks, shoelaces, and pants! Hiking poles & dog leashes, too.
Skin in different parts of the body reacts at different rates. If a rash develops in a new area a day or two after the first bumps, that’s likely the reason. Resin does not migrate over the skin or spread in the bloodstream.
Poison oak isn’t a problem in winter. As mentioned: Not true.
When the sap is running in early spring, and when there is lush foliage, it’s obviously worse, but those dead looking twigs can get you.
There are dietary measures that can reduce the severity of the allergic reaction. Wish that were true...but nope. Even in our county.
Eating poison oak or taking extract pills can reduce the intensity of the allergic reaction. There are some peculiar propositions out there for people with wishful thinking and disposable income. Please don’t do it. Urushiol probably does come through the GI tract with properties intact, and the first skin it finds at the other end...guess what.
This is quirky! Mango skin contains a bit of urushiol, and it can cause rashes on the cheek. Yes, that is true! It’s in the skin, not the flesh of the fruit. Not a bad idea to peel a mango with gloves, and give kids the peeled pieces, not the whole fruit.
Treatment
There are a lot of old wives’ tales out there, and even professionals are not always consistent in their advice regarding this common problem. It’s a little frustrating.
Old fashioned, over-the-counter (OTC) drying creams, oatmeal poultices, and shake lotions can help a bit with oozing skin conditions. There’s nothing much better than Calamine lotion to dry the poison oak blisters. (Coasters again: You’ll be drowning in an ocean...of Calamine lotion.) Do NOT, however, use skin remedies which contain antihistamines (like diphenhydramine) or local anesthetics. Why not?
They don’t work. Drat.
The added drugs can cause allergic reactions in their own right, and you can make things worse, not better.
If poison oak is becoming a plague for somebody in your family, it’s worth consulting a knowledgeable primary care doctor or a dermatologist for guidance.
Mild steroid creams, such as hydrocortisone cream, are available OTC without prescription. They are generally too weak to do much good for this problem, even if applied early, and they have virtually no benefit if the rash has gone to blisters.
Prescription steroids, oral steroids, shots, and other advanced measures require a visit with a licensed healthcare professional.
If you have been through this drill a few times, that professional might be willing to give you an anticipatory supply so you can get a right-away jump on treatment.
That makes sense if the patient has unavoidable exposures, such as a park ranger, landscaper, real cowboy, good shepherd, professional mountain biker, field biologist, land surveyor, or exuberant teenager.
Survival of the Fittest—Got that!
This resurgent poison oak plant sprouted right up through the soil of the catastrophic Carr Fire near Redding in 2018. Rangers initially thought it burned “down to mineral earth,” but the poison oak declared: Not dead yet.
Author Note: Wells Shoemaker MD is an avid hiker, backpacker, retired pediatrician, and author. Once a regular distance runner and a mountain biker in Nisene Marks, he has developed a 70+ year personal relationship with poison oak.
Photos by the author except web images of skin rash.
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