Here's information to help you avoid exposure - or failing that, how to treat an outbreak.
Poison oak, poison ivy (found east of the Cascades) and poison sumac share common blood: An oily sap, called urushiol (you-ROO-shee-ol), runs through their roots, stems and leaves. Urushiol is an allergen, and that's what makes poison oak wicked.
In sensitive people, the colorless or pale yellow oil sets off an allergic reaction causing redness, swelling, blisters and gosh-awful itching.
Poison oak is leafing out now, but no season is safe. "It is irritating in all conditions, all year round," says Gail Baker, an assistant professor of biology at Lane Community College who treks students to places such as Mount Pisgah Arboretum and Buford Park to talk about the weed.
Spring and summer are the worst, though, because the plants are juicy with sap and full with leaves.
Just brushing against the plant is enough to release the oil. You have a 15- to 20-minute grace period to wash off, ideally with soap. Remember under fingernails and rings, too.
After that, the oil fixes itself to proteins on your skin, says Dr. Frances Storrs, a dermatologist specializing in contact dermatitis at Oregon Health Sciences University in Portland. Your skin starts absorbing it, and trouble begins.
You can also pick up urushiol secondhand. It sticks to balls, golf clubs, garden tools and clothing, and can remain there for months. If you're around burning poison oak, oil particles in the smoke can settle on your skin. And the oil sneakily clings to Fido's fur.
"If little kids are getting it over and over," Storrs says, "it's probably coming from the family pet."
The rash usually arises 12 to 48 hours after exposure. It takes one to three weeks to heal. A bad case can make your skin darker or lighter for up to months.
An ounce of prevention: Smooth on a barrier cream, such as IvyArmor or IvyBlock, which contain chemicals to trap or block urushiol, preventing it from penetrating the skin. Wear long pants, long sleeves and boots during tromps in the woods. Launder clothes immediately upon return. Don gloves for yardwork. Wipe garden tools with rubbing alcohol.
You have a 15-20 minute grace period to wash off the oil from poison oak. In sensitive people, the oil can cause swelling, blisters and horrendous oozing and itching.
Here's a primer on the evil weed:
Q: What does poison oak look like?
A: In spring, three little leaflets unfurl from the stem, Baker says. Each leaflet is lobed, like a little oak leaf. New leaves are shiny red. They grow into a shiny green that loses luster as the season progresses and reach about an inch to 2 1/2 inches in length.
The plant has sprays of white flowers and, in fall, white berries. Its autumn leaves are crimson. "It can be very beautiful," Baker says. "I have heard of people gathering it to put in bouquets." Don't do that.
Q: Where does poison oak grow?
A: "Practically anywhere," says Richard Halfe, curator of the herbarium in the Department of Botany and Plant Pathology at Oregon State University. It can grow as a vine or a shrub, on fence rows, along stream beds, in the woods, up utility poles, in meadows.
Q: Who's allergic, and who's not?
A. About 15 percent of the population is resistant to poison oak, according to The American Academy of Dermatology. Sensitivity varies from person to person, and sensitivity can change over time. Allergic children can become less sensitive in adulthood.
You're not born allergic. You must be exposed to poison oak at least twice to react. Some are then immediately sensitive. Others could require dozens of exposures or may never reach the threshold.
Storrs, who has conducted research at OHSU on poison oak, guesses that no more than 30 percent of Oregon's population is allergic. Rash-free so far? "Don't be overconfident," advises Dr. Troy Richey, a Springfield dermatologist. "You can develop an allergy after many exposures."
Q: I'm allergic. What's with the rash?
A: Your skin is loaded with immune cells that are always on the lookout for trouble, says Richey, who calls poison oak rashes "an immune response gone haywire." The weed's sap is a harmless molecule that the body mistakes for an enemy. Cells release packets of histamine. Histamine helps dilate blood vessels, increasing blood flow to rush immune cells to the scene, says Dr. Patricia O'Hare, a dermatologist with PeaceHealth in Eugene. That also prompts the itching, redness and swelling.
Q: Can the rash spread?
A: No, even though it may seem like it. Thin skin, such as your face, absorbs urushiol more quickly than thick skin. So different parts of your body can break out at different times after the same exposure. Or you might be re-exposing yourself with oil under your nails or from a contaminated object. The fluid from a weepy rash is not contagious. Only urushiol can spread the rash.
Q: Why is scratching a no-no?
A: "People can break down their skin from scratching and get an infection from bacteria," says Dr. Gary Young, medical director of the emergency department at Sacred Heart Medical Center. Scratching can lead to scarring, too.
Q: What can I do at home?
A. If the rash is weeping, dermatologists recommend a drying soak such as a Burrow's or Domeboro solution. Ask the pharmacist if you can't find them. Either soak the area or make a compress, treating for about 15 minutes. Check with your doctor about how often to repeat. Lukewarm baths with baking soda or oatmeal - such as Aveeno - can also help dry the rash.
Cool showers are soothing. Applying baking-soda paste can relieve symptoms. Over-the-counter hydrocortisone creams will help reduce inflammation. Benadryl cream, an antihistamine, will calm the itching.
Dermatologists, however, prefer oral Benadryl because some patients develop an allergic rash from Benadryl cream. For the same reason, dermatologists frown on numbing calamine lotions. Regular calamine is OK.
One approach: Take oral Benadryl to quell itching; use hydrocortisone cream to treat inflammation.
Q: When should I see a doctor?
A: If you have swelling around the eyes, lips or tongue. If large areas of your body are affected. If the rash is on sensitive areas such as your face or genitals. If the rash is severe. If you're really miserable.
Q: What can doctors do?
A: They can prescribe a range of high-potency steroid creams, including a stronger version of hydrocortisone. When a cream won't cut it, they can prescribe a two-week course of prednisone, a steroid. "Oral prednisone brings normalcy back to life quicker than anything else," Richey says. "You give a low dose for a short duration. But it's a powerful drug with a lot of effects on the body, and you don't give it willy-nilly."
Q: How do I get rid of it in my yard?
A: Spring is a great time to kill new starts, says Pollyanna Lind of the Eugene-based Northwest Coalition for Alternatives to Pesticides. Wear protective clothing. Then grub starts out when the soil is soft, getting as much root as possible. Rake up the plants, bag in plastic and dispose. Do not compost; they'll grow there.
Then keep starts at bay by covering the area with a piece of carpeting and mulch. You need to plant something in its place or poison oak will re-establish itself. This process may need repeating for a few years.
Wait until leaves have dropped in the fall or winter to deal with larger, more robust poison oak.
Both the coalition and OSU Extension Service suggest fencing the affected area and letting a goat graze there for several years.
In Lane County's residential zones, a person is permitted to have one goat per half acre, says John Cole, land management director. Check with your city for its rules. Eugene, for example, allows goats in limited areas on lots of at least 20,000 square feet.
The Extension Service says two herbicides are effective against poison oak: triclotyr and glyphosate. Triclotyr can be purchased under several trade names, including Crossbow. Use it on a day when the temperature is 70 degrees or cooler. Glyphosate is also sold under multiple trade names, including Roundup. It is most effective in late summer or fall.
Tip: Roundup kills grass; Crossbow does not.
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