Now that it’s warming up and summer is approaching, everyone is getting back into their yards. I am also starting to see many cases of poison ivy in the clinic again. Just writing this article is making me itch.
The oil in the leaves of poison ivy (Toxicodendron radicans) is a common cause of contact dermatitis. An allergic reaction in the skin is called contact dermatitis. The poison ivy oil/chemical gets absorbed into the skin and changes the outside of the skin cells so that these cells look different to your body. Since these affected skin cells now look different than normal cells, your body’s immune system attacks these “foreign” (different-looking) cells. It is your immune system’s reaction to these cells that causes all of your symptoms, including the redness and unrelenting itch.
This allergic reaction is a delayed hypersensitivity reaction. You must have a previous exposure to the offending substance (the oil from the plant) which sensitizes your body’s immune response, so that the next time you are exposed to the same chemical, this immune response fires up and starts attacking the cells that have been exposed to the oil.
Why does poison ivy seem to spread?
The intensity of the reaction and how long it lasts depends on how much of the oil gets onto the skin, the thickness of the skin, and the amount of time it sits there before it is washed away. If your dog rolls in a patch of poison ivy and you pet your dog while it is still covered in poison ivy oil or the plant itself, you can have an allergic reaction from this exposure, although it’s not as common as coming into contact with the poison ivy plant yourself. If your hands come in contact with poison ivy, then you rub your eye, or your arm (before you wash it off your hands), then the poison ivy spreads to that area. You spread a little oil to new areas with each touch, scratch or rub and the rash and itch seems to spread.
How long it takes for you to have a reaction to poison ivy once you are exposed depends a lot on the thickness of skin. On the palms of your hands, the skin is thick and it takes more oil and time for a reaction to occur. Around your eyes, inner arms, and backs of hands, the skin is thinner and it takes less oil and time of exposure to react.
Can you spread it when you pop the blisters that form?
No, only the oil spreads the rash, and once it binds with the proteins in your skin, it can no longer be spread. Blisters occur over a period of 24 to 48 hours after exposure and these blisters result from the damage to your skin by the immune response and the fluid they contain is from this response.
How long will the itch last?
After the rash appears it usually runs for two to four weeks. However, this will depend upon your poison ivy time of exposure, how much you were exposed to, and how quickly you get started on medications to help turn off the allergic reaction.
What can I do to prevent it?
Avoidance is the best. But make sure to wear long sleeves, long pants and gloves if you know you may come in contact with poison ivy. After possible exposure, before you go inside undress and wash/shower off with soap. This will help to remove the oil before it has a chance to irritate your skin and start the immune reaction. Know what the poison ivy plant looks like, so you can avoid it.
When patients come to the clinic, the reaction is usually already significant and we will usually treat with steroids in shot or pill form. There are some over-the-counter medications that may help, such as antihistamines and some topical agents (talk to your pharmacist). If your reaction is severe, it’s probably best to come to the clinic.
— This article was written by Barry Holdampf, MD, a family practice physician who joined the Scott & White Taylor Clinic in November 2010. He specializes in providing medical care to families, including pediatric and adult patients.