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


Please note this login is to submit events or press releases. Use this page here to login for your Independent subscription

Not a member? Sign up here.