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From Oil to Rash

The urushiol found in the sap of the poison ivy plant binds to skin cells when it comes into contact, says Ziska.

Touching the sap of the plant as well as touching something on which urushiol is present, such as garden tools, can result in an allergic reaction, according to the American Academy of Dermatology (AAD). Burning poison ivy plants can release urushiol particles into the air.

When the oil gets on the skin, it can penetrate in minutes, according to the AAD.

"Once it is absorbed, there is not much you can do," Ziska adds.

"Most people don't know they have come into contact until hours later or even longer, when they start reacting," says David Peng, MD, assistant professor of clinical dermatology at the University of Southern California Keck School of Medicine, Los Angeles. He runs the contact dermatitis clinic at USC, and poison ivy rash is a kind of contact dermatitis.

Typically, there is itching, redness, swelling, and the rash, according to the AAD.

"It can take hours to days to exhibit the rash," says Ronald Brancaccio, MD, clinical professor of dermatology at the New York University School of Medicine and a practicing dermatologist at the Skin Institute of New York. A reaction usually occurs within 12 to 48 hours, the AAD estimates.

Pre-emptive Poison Ivy Plan

Since the poison ivy rash can take its time in showing up, experts recommend a pre-emptive strike approach.

"If you think you have come into contact, wash the [oil] off first, using rubbing alcohol," Peng says. Then use plain hot water. Then use soap and hot water. Discard the soap, and wash the washcloth."

Brancaccio says it's good enough to wash with plain soap and water of any temperature and OK to skip the alcohol and plain water steps.

If you're out on a hiking trail or camping, use cold water from a stream or other source, the AAD recommends, and the sooner the better.

Once you've washed the oil off your skin, you are not contagious and cannot give the poison ivy rash to someone else.

All experts agree on one point, however: launder the clothes you wore when exposed to the poison ivy as well as tents and other camping gear. The oil can stick to clothing and re-expose you.