Potent Poison ; Ivy, Oak, Sumac Pack Powerful Potential for Irritating Skin Rash

Just one billionth of a gram of this substance has the potential for causing an irritating skin rash in some individuals, though 100 times that amount is the average for most people.

This chemical is so potent that one-fourth of an ounce is enough to make every man, woman and child on the earth break out in an intolerable, tormenting itch that may last for days.

We’re not talking about some super powerful man-made biological WMM (weapon of mass misery) here, some evil concoction brewed up in the labs of would-be terrorists. We’re speaking of Mother Nature’s very own formulation, a compound called urushiol — the oil manufactured by and found in plants commonly known as poison ivy, poison oak and poison sumac (among others).

Ironically, urushiol is incapable of causing harm on its own. It accomplishes its dirty work by eliciting a localized allergic reaction. It’s as if this oily substance coerces the body to mutilate itself.

An allergic reaction to poison ivy does not usually become apparent until several hours after exposure.

But Dr. Martha Buchanan, assistant public health director at the Knox County Health Department, says some exposed areas of the skin may react more slowly than others, “and that leads to the erroneous impression that the rash is spreading.”

Very briefly, here’s what goes on beneath the skin after your outer skin layer, the epidermis, comes in contact with urushiol. Soon after contact,the chemical diffuses down into the second layer of skin, the dermis.

Here blood cells called T lymphocytes identify the substance as a foreign agent and respond by releasing substances called cytokines. These in turn summon and activate millions of white blood cells called monocytes. They chew up just about everything in site, and so we get the typical redness, itchiness, swelling, blistering, peeling, etc.

And what if you do come into contact with urushiol? What should you do?

Washing off the sap will lessen the reaction, but only if you wash it off before it has a chance to penetrate into the next skin layer.

Experts say use isopropyl (rubbing) alcohol first. Then wash skin with water, not soap. The soap will dissolve some oil and spread it around.

Finally, take a regular shower with soap and warm water.

Any items that may have come in contact with the plant should be washed off with alcohol and water. Use gloves for this task.

The rash, blisters and itch usually go away within 14 to 20 days on their own. But the discomfort is so great that few are able to endure the period without taking something for relief. Wet compresses or soaking in cool water and oral antihistamines may be helpful for mild cases.

Buchanan said that topical corticosteroids commonly called hydrocortisones may be safe and effective for temporary relief of itching associated with poison ivy.Over-the-counter and home remedies include baking soda Aveeno (oatmeal bath), aluminum hydroxide gel, calamine lotion, kaolin and zinc acetate.

For severe cases, however, Buchanan says, doctors may prescribe oral or injectionable corticosteroid drugs that may stop the reaction.

Just always err on the side of caution if you think you might come in contact with these plants, wear protective clothing.

Knoxville writer Douglas Hullander writes “Science in Your World” for the News Sentinel. He may be reached by e-mail at doughullander1@comcast.net.

Myth Busters

Down through the years, these plants and the discomfort they inflict have spawned numerous myths.

Among them:

* Poison Ivy is contagious.

Not so. Only direct skin contact with the oil of the plant can cause the allergic reaction. The liquid in the blisters does not contain the oil, so coming in contact with these excretions will not spread the rash to another person.

Likewise, the liquid will not cause further spreading of the rash should the blisters burst.

Still, its not wise to scratch until the lesions rupture because you simply increase the chances for initiating an infection.

* You can get the rash by simply being near the plants.

False. But if the oil were to become airborne during a fire, for instance, or if the plant were being cut with a mower or trimmer, theres a good chance, if youre close enough, that some of the urushiol could find its way to your skin surface, even your respiratory tract.

* Leaves of three, let them be.

Thats usually good advice where poison oak and poison ivy are concerned, but poison sumac has seven to 13 leaves per branch. So beware.

* Youve been exposed to the leaves of poison ivy numerous times and havent broken out yet, so youre immune.

Not necessarily. Youre probably just very lucky. Experts say 90 percent of people are allergic to the oil, and the more youre exposed, the more likely you are to become sensitized, so for most of us, its just a matter of time.

* Poison oak causes a lot of blisters, but poison ivy causes a less severe skin rash.

Thats false too. Because all three plants produce urushiol, the effects of each are very similar.

* Theres only one form of poison ivy.

No. Actually, poison ivy can look like a shrub or a creep like a vine. Poison ivy leaves vary considerably, too, with respect to the degree the leaves are toothed.

* Eating poison ivy will grant you immunity.

No way.

* Poison ivy is transported throughout the body by the blood stream.

Not true.

* Dead plants are OK to touch.

False. They may still contain the oil long after the plant has died. And the sap may remain active for years on the surface of inanimate objects.