Roughly half of all adults in the United States are sensitive to poison oak and poison ivy. This year alone, 40 to 60 million people will suffer at least one bout of the rash these plants cause. Poison oak and poison ivy are botanically and chemically related. Poison ivy tends to grow east of the Rockies, and poison oak tends to grow in the western states, although there is some crossover. And a person sensitive to poison ivy will also react to poison oak.
Where It Grows
Poison oak ranges from southern Canada all the way to Baja, Mexico. It grows nicely at the ocean shore and flourishes along streams and in foothills where it is hot in summer and wet in winter. It grows poorly above 4,000 feet, in rain forests, and in the desert. Its leaves vary from bright green to red; in winter, it looks dead. But beware: the poisonous oil is always there.
What It Looks Like
It is vital to know what the plant looks like. The common saying „leaves three, leave it be” is only partially correct. Poison oak leaves cluster in groups of three, five, seven, or nine. To make matters worse, the plant’s appearance differs in different parts of the West. Poison oak in Northern California doesn’t resemble the plant in Southern California.
The poisonous oil, called urushiol, is a light, almost colorless substance found throughout the plant in leaves, berries, stalks and roots. It oozes out whenever these fragile structures are traumatized. The oil, which cannot be seen easily, settles onto skin and quickly penetrates. Once out of the plant, the oil rapidly oxidizes and forms a polymer that resembles Japanese black lacquer. During the summer, along dusty and well-traveled roads, or in areas of high wind, the black lacquer of urushiol can be seen on many trees. It is still active and a little-recognized source of poison oak exposure. Pets are another unexpected source. The oil attaches to the fur of dogs and cats, who generally aren’t bothered by it but promptly transmit it to their owners.
We’re not born sensitive to poison oak; we acquire sensitivity through exposure. The first exposure generally occurs in childhood, causing little or no reaction. However, it sets in motion the immunologic machinery called „contact sensitization.” On the next exposure-perhaps a year or more later-a horrendous rash may appear within two days of a brush with poison oak. Often the rash is so severe it’s remembered for life.
Not all adults are equally sensitive. Of the estimated 125 million sensitive people in the U.S., about 15 to 20 percent are exquisitely sensitive. They get a severe, explosive eruption that arises within hours to a day after exposure. Inflammation, swelling and blisters spread throughout the skin. This type of reaction is a medical emergency and requires treatment by a doctor.
Mild to Moderate Reactions
Most adults are mildly to moderately sensitive. After exposure, a rash appears within two to four days. While annoying, the rash heals spontaneously in seven to ten days, with or without treatment. Most sufferers don’t seek a physician’s help but go to the local drugstore for over-the-counter medications.
Of the fortunate 50 percent of American adults who consider themselves insensitive to poison oak or ivy, most are actually „subclinically” sensitive. They react, but only if they get a massive exposure or are tested with large amounts of purified urushiol. They are not immune, and may spontaneously become sensitive in middle age. Only about 10 to 15 percent of the U.S. population is truly immune or tolerant to poison oak.
Sensitivity Can Change
An individual’s level of sensitivity varies over a lifetime; it doesn’t change quickly, but a person who is very sensitive as a child may be just moderately sensitive as an adult. A lucky few lose their sensitivity altogether as they age, probably through lack of exposure.
Avoiding the plant is the best way to prevent poison oak dermatitis. Wearing protective clothing is a must. Barrier preparations can be helpful as well; the best one on the market is called Stokogard Outdoor Creme. Ask your pharmacist to order it from Stockhausen in North Carolina. It is an oily substance that binds specifically to urushiol and holds it from the skin. However, it is an inelegant, oily, greasy preparation which smells like dead fish for the first minute or so after application, although it’s not noticeable after that. After four to eight hours, it must be washed off. Otherwise, it begins to release bound urushiol, which gradually penetrates the skin.
Removing the Oil
If you do have a brush with poison oak, solvents such as acetone, rubbing alcohol, gasoline, or paint thinner can remove the oil. Apply liberal amounts of isopropyl alcohol to the skin, including the face and hands. Rinse with large amounts of water. (If the alcohol evaporates on the skin, the oil is transported to another area rather than removed.) Since alcohol also removes protective oils from the skin, a new exposure before the oils are replenished will cause even more trouble.
Water not only flushes the alcohol from the skin but tends to slowly oxidize (inactivate) urushiol. This oxidizing effect can be enhanced by adding bleach, hydrogen peroxide, or hypochlorite.
Clean all poison oak-contaminated objects, such as golf clubs, hunting gear, shovels, or picks, before packing up. At home, clothes, including shoes, should be taken off and washed. If urushiol is on the seat of your pants and you sit down in a chair, the oil will be in the chair, waiting for the next person to sit down.
Treatment varies with the rash’s severity. The most sensitive individuals, who rapidly develop a severe eruption, must immediately go to their physician or dermatologist. The inflammation can be reduced with systemic corticosteroids. The sooner treatment starts, the more effective it will be.
Unfortunately, mildly to moderately sensitive individuals don’t respond well to any treatment. Systemic corticosteroids aren’t useful, and topical over-the-counter corticosteroids-even potent ones-have relatively little effect. To help relieve the itching, take cool soaks in a tub containing Aveeno, bicarbonate of soda, or vinegar. Applying calamine lotion may help. Additives such as Benadryl or lidocaine add little to calamine except cost. Histamine release is a minor component of poison oak inflammation, so antihistamines generally don’t help. In children, antihistamines may be useful if given at bedtime since their sedative properties help reduce scratching at night.
Can you become desensitized by taking urushiol by mouth? In a word, no. In 1993, the Food and Drug Administration forced a recall of all such products on the market. However, a small company in San Mateo, California, is working on a preventive vaccine they expect to market in three to four years.
Until then, your best course is to stay out of harm’s way-or quickly decontaminate yourself if you do encounter the aggravating weed.