Blistering Hike

Beware the Poison Oak

by Virginia Hayes

All that late rain was great for the shrubs of the chaparral and riparian woodlands that make up our local flora. It resulted in great displays of spring flowers, but there is one native that most of us could do without: poison oak (Toxicodendron diversilobum), which is widespread in most of the plant communities in our backcountry. Enjoying such outdoor activities as hiking and rock climbing can lead to an irritating encounter with this shrub.

Hopefully you know whether you are among the 85 to 90 percent of the populace that reacts to this species and can take measures to avoid it or mitigate its effects if you accidentally stumble upon it. Usually, it takes actual physical contact with some part of the plant to trigger the allergic reaction, but be aware that pollen from the flowers and smoke from burning the plant can also cause trouble. It’s not supposed to happen, but reports of volatilized oil on hot days causing outbreaks are not uncommon either. This time of year, the bright and glossy leaves are easy to spot and in fall when they become a blaze of red they are even pretty to look at. In the winter, though, the deciduous stems can be just as toxic, but much harder to spot. In some really old specimens, bare vines as big as your wrist may snake way up into the tree canopy before showing any leaves. Since poison oak doesn’t confine itself to the wild, it may still rear its ugly head in backyards of our more rural areas too. Clearing weeds or just trekking through the underbrush can bring you in contact with these innocent-looking creepers. The result will not be pleasant.

If you don’t know how sensitive you might be, it’s best to learn what poison oak looks like and avoid it. The old adage “leaves in threes, leave it be” works pretty well. Typically, the leaves are arranged in triplets on the end of short stalks. In California, they are almost uniformly lobed and reminiscent of the oak tree from which they take their common name. It may be hard to stay completely away since it is so common along most local hiking trails. There are heroic souls who volunteer to keep trails cleared of this health hazard, but they can’t keep up on years like this, so vigilance is required. The active ingredient that causes all this grief is urushiol. As little as one nanogram (a billionth of a gram) is enough to set off the immune response. The chemical is remarkably long-lasting too. It can persist in dead plants for one to five years (even centuries-old specimens have caused a rash in sensitive people). It may take from a few hours to several days to manifest itself and some parts of your body will be more sensitive than others. That soft skin under your chin or behind your knees will erupt with blisters faster than your toughened feet. The itching will then begin. In fact, that will probably be your first clue that something is amiss. By then it is too late to really intercept the oil and you will just have to treat the dermatitis with topical ointments and salves. Those containing hydrocortisone are the most effective at this stage. If you know that you have been in contact with the plant, you do have some options to reduce the exposure. Since it is an oil, urushiol is removed from the skin by a solvent or soap. Use straight alcohol or something like witch hazel that contains a lot of alcohol, or another oil such as baby oil or vegetable oil (I’ve even heard of using mayonnaise!) to wipe yourself down, and then work up a good lather with hand soap or dishwashing detergent. If you don’t have access to any of these, wash in cold water. Lots of it. It will only spread the oil around if you don’t get it completely rinsed off. The sooner the better is also good advice because urushiol has a way of being absorbed into the skin cells and forming bonds there that are hard to break. This process can take as few as 15 minutes, but is probably more like a few hours.

Most people recover from the localized rash in a little over a week. Others of us are extremely sensitive and may have a system-wide reaction. If severe enough, some sufferers have required hospitalization and large doses of corticosteroids to reduce the inflammation — another good reason to just keep away from poison oak.

Virginia Hayes, curator of Ganna Walska Lotusland, will answer your gardening questions. Address them to Gardens, The Independent, 122 W. Figueroa St., S.B., CA 93101. Send email to

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