The Big Three: Poison Oak, Ivy and Sumac

A leisurely day hike, a challenging trail run or a weekend camping trip can provide great relaxation, help maintain fitness and reduce stress.

But pursuing the wonders of nature can also have drawbacks.

In addition to the potential dangers of the sun's rays and the discomfort of insect bites, outdoor enthusiasts should be aware of the evils of a trio of problematic plants - poison oak, poison ivy and poison sumac.

According to the American Academy of Dermatology in Schaumburg, Ill., the toxic oily resin from the plants are among the country's most common allergic reactions.

As many as 50 million North Americans are affected per year.

And for those active in the great outdoors, there's little escape. With the exception of Hawaii, Alaska and some desert areas of Nevada, the weed is prevalent throughout the United States in its three regional varieties:

* Poison oak - A low-lying shrub or small tree or vine with three or five leaflets and clusters of yellow berries, is found in the West and Southwest. The plant's leaves turn a deep red in the fall.

* Poison ivy - A low-growing shrub or vine with green-yellow flowers and white berries, is dominant east of the Rockies, but also grows in other regions.

* Poison sumac - A tall rangy shrub with 7-13 leaves and cream-colored berries primarily located in the Great Lakes regions and in swamps and bogs east of the Mississippi River.

Although all three plants flourish in the spring and summer, allergic reactions can occur in the fall and winter when the plants' sticks and vines are mistakeningly used as firewood or in holiday wreaths.

"We get a lot of calls in the winter from people who have think they may have inhaled the toxic oil after they've burned their fields," said a spokesman at the Regional Poison Control Center in Sacramento, Calif. "It can be very dangerous if you get poison oak, ivy or sumac in your lungs. Firefighters are very susceptible."

The "poison" in each of the three plants is the result of an allergic reaction to urishiol, the colorless or slightly yellow oil that oozes from any cut or crushed part of the plant.