Dear Dr. K: A co-worker came to work with a poison ivy rash. She assured me she's not contagious. Is that true?
Dear Reader: Your co-worker is right: You can't "catch" poison ivy from coming into contact with her rash. But it's summer, so let me give you a refresher course about the many plants that can cause a rash and how to take precautions against them. That way you'll be as safe while gardening in your backyard, biking in a park or hiking in the mountains as you are sitting beside your co-worker in your office.
Many plants have defenses to protect themselves. Some secrete oils or saps that cause animals and humans to develop allergic reactions. If you touch the plant, the contact triggers an allergic reaction that appears in two to 10 days as a red, swollen, itchy, blistering rash. Poison ivy, poison oak and poison sumac are best known for causing the problem. (I've put an illustration of these plants on my website, AskDoctorK.com, so you'll know what to avoid when you're outdoors.)
If you do encounter one of these plants, the allergic reaction will go away on its own in about 10 days. But you'll likely be desperate for relief from the burning, itching sensation long before then.
My colleague at Harvard Medical School, dermatologist Dr. Kenneth Arndt, shared some tips for relieving symptoms. First, apply cool compresses, then pat your skin dry. Try an over-the-counter hydrocortisone cream. If that's not strong enough, ask your doctor to prescribe a more potent steroid cream. You'll have to apply the cream a few times a day until the rash clears up.
Of course, it's better to avoid the rash in the first place. That means protecting yourself when you're outside. Wear long sleeves and pants, as well as thick work gloves, when gardening. Be careful about those clothes and gloves. They may have kept plant oils off your skin while you were outdoors, brushing against poison ivy, but those oils remain on clothes and gloves for several days. So if after you come indoors you touch the outside of the unwashed clothes or gloves, you could transfer the oils to your skin and get poison ivy.
If you think any part of your body may have come in contact with poisonous plants, wash the area with soap and water as soon as you can. The faster you wash, the more effective it will be. If you wash immediately, most of the plant oil will come off. If you wait more than two hours, it's too late.
Don't forget to always wash your hands, even if you don't think they touched a plant. Your hands may not have touched the plant, but they could well have touched the part of you that touched the plant. And when you wash your hands, scrub under your fingernails, as that's a place that oils like to hide.
Dr. Komaroff is a physician and professor at Harvard Medical School. See his website to send questions and get additional information: www.AskDoctorK.com.