Is there a vaccine for poison ivy?

. . . When I was a girl in the 1940s and got poison ivy all the time, they gave me tincture of poison ivy, in graduated doses, and it calmed the allergy down. Is there anything like that now?
L.W, Newton

Nope, sorry. And you must have been one of the lucky ones as a kid.

In decades past, doctors did try exactly what you remember -- giving small doses of the allergy-causing substance from poison ivy in hopes of making people's immune systems more tolerant of poison ivy. But these attempts usually failed, and sometimes made people worse, said Dr. Robert Stern, chief of dermatology at Beth Israel Deaconess Medical Center.

If doctors gave the substance orally, it passed through the digestive system and caused a red, itchy rash in a particularly unpleasant place, the rectum. If they tried to desensitize people by rubbing a tiny bit of poison ivy on the skin, that elicited exactly the response they were trying to avoid -- a red, itchy skin rash.

Unlike allergic reactions to things like pollen, with poison ivy the exaggerated immune response is not triggered by antibodies but by cells called T cells. The first exposure to poison ivy won't do much, but the second time the T cells are primed to pump out chemicals that trigger inflammation.

Even if there were a good way to desensitize a person to poison ivy, it might be dangerous, said Dr. Mariana Castells, codirector of the allergy and clinical immunology training program at Brigham and Women's Hospital. If you "tolerized" people to the substance in poison ivy, "you might tolerize people to things they should be reacting to," like viruses and bacteria, she said.

Bottom line? Stay away from poison ivy if you can (and don't burn it if you're cleaning up your garden!) If you do get a poison-ivy rash, wash it gently with water (no soap), use oral antihistamines like Benadryl or anti-itch lotions, and topical steroids like Clobetasol. If that fails, your doctor may prescribe an oral steroid such as Prednisone.

JUDY FOREMAN