Rash Statements
For: Ask the Experts, October 2002
The rash caused by poison ivy is an immune-system reaction
to an oil called urushiol (uh-ROO-she-all) that occurs in the sap of the
plant genus Toxicodendron. Poison ivy, oak, and sumac all belong
to this genus (cashews and mangos are close relatives).
How can you avoid an outbreak?
Stay away from the plants, if you can. Wear protective clothing, including
gloves, when out in the woods or working in the yard. Learn to recognize
the leaves and berries of the toxicodendrons common to your area.
The FDA recently approved a nonprescription liquid called
Ivy Block ($12 for 4 ounces) that has been shown to prevent or minimize
the rash. Its active ingredient is bentoquatum—a clay filler that
blocks absorption of urushiol. It may be useful for those who work and
play outdoors and can't avoid the plants. (It has not been tested
on children under 6.) You spread it on your skin before exposure; it leaves
a visible coating so you can tell where it is.
Will eating a few leaves of the plant
desensitize you? Not at all. And it may make you very sick.
Do pets get poison ivy? No,
but they can carry urushiol on their fur and spread it to you. Bathe your
pet, wearing gloves, if you think it has brushed against a toxicodendron.
Will scratching the rash (and breaking
the blisters) cause it to spread? No. The water inside the blisters
does not contain urushiol. But try not to scratch anyway, because scratching
can lead to infection. If the rash seems to have spread to areas of your
body that were protected by clothing, you may unknowingly have had urushiol
on your hands or clothing and spread it. If you think you've been
exposed, be careful when undressing.
How do you get rid of urushiol once
it is on your skin or clothing? If you think you have been exposed,
wash the area with soap and lots of water within 5 to 10 minutes, if possible.
The longer you wait, the less effective washing becomes. If you're
out in the woods, use water from a lake or stream, premoistened towelettes,
rubbing alcohol, or even soda or beer from the picnic basket. Wear gloves
to remove clothing and shoes. Wash clothes in strong detergent, and wipe
off shoes. Urushiol is very durable. If you don't wash it off shoes,
garden tools, and other items, it will still be there many months hence
and can cause a reaction.
Can the rash be transmitted from
person to person? No. By the time the rash appears, the urushiol
is gone. In theory, if you have urushiol on your skin—that is, after
exposure to the plant but before the rash appears, you might transmit
the oil by touching someone. But this is not a common means of transmission.
Is anyone immune to poison ivy?
It's thought that up to 70% of us are sensitive. But you may not
start reacting until you've been exposed a few times. Never count
on being immune.
Are there areas where the plants
don't grow? Toxicodendrons are common nearly everywhere from
Mexico to Canada. The only states that have none are Nevada, Hawaii, and
Alaska. Some states have no poison ivy but do have poison oak.
Is it just the leaves that cause
the problem? All parts of the plant can be toxic, even if dead.
If you are trying to rid your yard of it, you can kill it with a herbicide,
but you'll still need to wear heavy protective gloves and clothing
when removing the "corpses."
Is it a good idea to burn the plants?
No, that can release urushiol into the air. This is a danger in forest
fires, especially for firefighters.
How can you relieve the itch? Cool compresses, cool baths, calamine lotion or cream, baking soda baths or compresses, or colloidal oatmeal baths all have their advocates. Nonprescription cortisone creams can also help. The rash usually lasts less than three weeks and itches less as time goes on. But if it is widespread and very painful, see a doctor, who may prescribe a corticoid product.
UC Berkeley Wellness Letter, August 1997
