Poison Oak - A General Overview

By Matt Pritchard

Let's start with one undeniable fact - Poison Oak sucks. This isn't open for debate, nor does this come as breaking news to those with memories of oozing rashes and tireless itching. Yep, Poison Oak (and its evil twin Poison Ivy) is an unfortunate reality for most hikers. Here in the Bay Area, most of our foothills host pockets of the stuff and it's usually just a matter of time before you have your first dance with an itchy rash and a bottle of Calamine lotion.

Probably the most interesting thing about Poison Oak is the amount of bad information swirling around. Maybe people just want to think the worst of this plant, but some of the "facts" you hear in conversation with seemingly well-informed people are largely B.S. I'm not a doctor, but I've done my research and I decided to write this little article to clear up a few points.

What exactly is Poison Oak?

Green Poison Oak Red Poison Oak

Poison Oak is an obnoxious little plant, native to the West Coast of North America. The plant's taxonomical name is Toxicodendron Diversilobum - the first word literally meaning "poison tree". It typically appears as a vine or shrub with clusters of three leaves. The plants are usually low lying, but can grow quite tall (6 feet plus). The leaves themselves appear similar in shape to an oak leaf, with rounded points and noticeable veining. In the springtime, the leaves take on a reddish hue which eventually gives way to green in the summer. The leaves usually have a slight luster to them - this is the shiny urushiol oil. See the images at right. Notice the variation in color, but the consistent shape of the leaves.

What's the deal with the rash?

Contact with the Urushiol oil of a Poison Oak plant can cause a form of contact dermatitis - an itchy rash that often causes localized swelling and blistering of the exposed skin. Absorption of the oil after contact usually takes anywhere from 30 minutes to several hours, giving you time to take action if possible. Most people will develop a rash a few days after exposure. I, personally, usually see a rash appear a week after exposure, but more recently have seen it appear after only two or three days.

The rash usually appears as a red, swollen patch of skin that itches like a sumbitch. The rash will sometimes develop blisters, which may ooze, or "weep". The fluid from these blisters is not Urushiol and cannot spread the Poison Oak rash to other people or other parts of your body.

How do I treat the rash once it appears?

First and foremost - don't scratch the rash, no matter how bad it itches. Second, keep it as clean as possible. If you follow just these two rules, the rash will usually fade away within a week or two. No treatment can make the rash disappear any faster, but several topical medications can help ease the symptoms. Calamine lotion or newer calamine gels can help reduce the itching and make your life much more comfortable. I swear by Oak-n-Ivy Calagel. It has always made a big difference for me when I've used it in the past. These treatments are widely available at drug stores.

Large rashes, rashes that appear infected, and any rash that is accompanied by a fever should be examined by a doctor. The doctor may prescribe a corticosteroid to ease the swelling and itching associated with the rash.

Is Poison Oak contagious? Can it spread to other parts of your body?

The simple answer to both questions is "No". The not-so-simple answer is "Well, maybe, but probably not." Only urushiol can cause the reaction of contact dermatitis. Once you've touched (or brushed up against) urushiol, the oil itself can be spread by contact to other parts of your body, clothes, friends, etc. After you've quarantined your clothes and gear and had a decent shower, you are clean. The rash may still appear, but you've stopped the possibility of "spreading" the oil any further.

Aside from being gross, the blistered appearance and weeping of the rash often lead the misinformed to presume it is contagious. It is not. Again, unless you are a totally filthy bastard that hasn't had a good shower since your initial exposure, all of the urushiol was probably washed off well before the rash even appeared. Everyone repeat after me - "POISON OAK IS NOT CONTAGIOUS".

As mentioned above, the rash usually takes a day to several days to appear after exposure. Often, the rash appears sooner in some exposed places than others (e.g. Tuesday it appears on your legs and on Thursday you find some on your arm). This often leads people to believe the rash is spreading. I subscribe to the concept that Poison Oak can't be spread after the oil has been neutralized.

However, I've recently heard from two different sources that Poison Oak can spread through your blood stream and/or lymphatic system. I think this misconception is rooted in the fact that the basic physiological reaction to Urushiol does involve your T-cells and lymph nodes. The concept of "internal" spreading seems highly implausible to me, but my research hasn't turned up any indisputable evidence either way, so I'll leave this one open for debate. If you happen to be a dermatologist or expert in the field of plant toxicology, I'd love to hear from you on this point. Please contact me here.

How can I keep from getting it?

Wear a Haz-Mat suit during every hike and you'll be A-OK. Assuming this is unreasonable, there are still some simple precautions you can take to minimize your chances of exposure. First and foremost, learn how to identify Poison Oak - see the description and pictures above. Avoiding the plant is a simple solution, but sometimes you don't see it coming or even notice you've come into contact with it. Covering your skin while hiking can greatly reduce your chance of exposure. Wearing pants (especially) and long sleeved shirts while hiking is a simple solution. If you see poison oak at any point during your hike, assume you've come into contact and take the following precautions.

  • Try to avoid any hand to face contact until you've had a chance to thoroughly wash your hands.
  • Once you arrive at your car or at home, strip off your shoes and clothes and quarantine them in a garbage sack. After showering, wash your clothes as you normally would and wipe down your shoes/boots with warm, soapy water.
  • Take a shower using plenty of soap and some decidedly aggressive scrubbing. Urushiol is a sticky substance and may persist through one washing. When in doubt, soap up twice.
  • Alternatively, you can use a mineral sprit-based product like Tecnu to strip away any Urushiol on your body. If you do use Tecnu, you'll probably want to shower also, which delivers the best one, two combination and reduces your chances of getting a rash.

One final note about avoiding Poison Oak has to do with the beloved family pet. Dogs and cats that spend time outside often frequent the areas that Poison Oak calls home - you can't blame them, there's just too many good smells. While dogs and cats aren't allergic to Poison Oak themselves, they can carry it back home on their fur and contaminate anyone that pets them or even brushes against them. If your pets have been in an area known for Poison Oak, take the time to give them a good bath.

Are some people immune to Poison Oak? Can I build immunity?

Sensitivity to Poison Oak varies from person to person. Some people show no symptoms or rash even after repeated exposures, while others present acute reactions after casual encounters with the stuff. Immunity from Poison Oak isn't really possible, in the traditional sense. People that seem to be immune can still be surprised by an outbreak when all of the biological conditions are just so. This article published by the American Botanical Council treats the subject with far greater detail for those who are interested. Even if you think you're immune, it is worth your while to take the precautions discussed above after exposure.

What about building immunity by repeated, controlled exposure, or God forbid ingestion of the plant? NO - not gonna happen - don't even try it. In fact, some research suggests that repeated exposure to Poison Oak may increase a person's sensitivity to its toxins, especially in localized areas that have presented rashes in the past.

Other Resources

Poison Ivy, Oak, and Sumac Information Center

American Botanical Council article on Poison Oak

WebMD article on the subject

Questions or comments about this article? Let us know.