With half of the U.S. population sensitive to poison ivy and more and more people venturing into the wilderness, episodes of poison ivy dermatitis are increasing.

Poison ivy is difficult to identify. East of the Rocky Mountains, poison ivy tends to grow as a climbing vine on trees, poles and houses. West of the Rockies, poison oak grows as small bushes and sometimes in a dense forest can be a climbing vine.These weeds tend not to grow above 4,000 feet elevation. The Rocky and Sierra Nevada mountain ranges are safe. The weeds do not grow in hot, dry deserts unless rain and water are bountiful.

Although half of us are reactive, only 15-25 percent will respond with incapacitating swelling, blistering eruptions requiring treatment with systematic corticosteroids and significant loss of time from work.

There is no routine way to learn one's degree of sensitivity. The most reliable method is a history of past dermatitis.

The resin (urushiol) is a colorless or slightly yellow, light oil. It runs in resin canals just under the surface, running from the roots through the stems, into the leaves and flowers, and just under the surface of the fruit of these plants. It does not appear in the nectar sucked by honey bees. The leaves of the weeds are very fragile and easily ruptured by high winds or brushing by humans or animals. The light oil immediately oozes onto the surface, where it turns black (known as the "black spot test").

When the light oil oozes onto human skin, one generally cannot see it. If it is on the sole of a shoe or the palm of a hand or glove, it can be spread to other areas by direct contact. The oil may stay on the surface of animal fur. On some objects, the oil can stay in an active form for months or years.

Smoke blown by the wind can produce very severe airborne dermatitis. This almost never occurs with professional firefighters but is reported with volunteer firefighters or people on picnics downwind from a campsite. These episodes need emergency medical care.

Clothes act as a barrier. There are topical barriers that can act as binders.

Probably the best barrier preparation available is Stokogard Outdoor Cream. Because of FDA constraints, it is sold only through industrial supply outlets with no advertising of its protective value against poison ivy/oak. Although it is sticky and not especially elegant, it should be applied to shoes, clothing and skin that will be exposed to the weeds and then washed off within 4 to 8 hours afterward.

Ivy Shield is sold in pharmaceutical outlets. It binds the resin (urushiol) and slowly releases it onto the skin. Its status with the FDA remains unclear at present. It may no longer be available. Ivy Block is another good barrier preparation.

Decontamination with isopropyl alcohol used liberally (not in swab-type dabs) is recommended. If used with too little isopropyl alcohol, the oil will actually be spread to another site and enlarge the injury. Other solvents could be used (e.g., paint thinner or gasoline), but they are hard on the skin.

Water removes urushiol from the skin, and oxidizes and inactivates it. Water does not penetrate the skin as do solvents. Following solvent application, water will clear all solubilized material off the skin. It should be used liberally.

Hydrogen peroxide, (an oxidizing agent) works effectively. When mixed with water, hydrogen peroxide can be even more effective.

Sensitive people need to have the urushiol washed off immediately, and moderately sensitive people have about an hour for rinsing. The sooner the decontamination is started, the better (probably between 1 and 4 hours).

Summary

Reduce poison ivy dermatitis with the following steps:

1. Avoid the plants.

2. Wear protective clothing and use appropriate barrier preparations.

3. Replenish the barrier protection every 4 to 6 hours if practical.

4. Decontaminate after known exposure with liberal amount of water and then reapply the barrier preparation.

5. Decontaminate at the end of the day with isopropyl alcohol and water rinse.

6. Dispose of all contaminated clothing and equipment.