Having treated thousands of cases of poison oak in my career, I’d like to share with you what I’ve learned about this miserable affliction.
The poison oak plant which is so prevalent in our locale, contains an oil in its sap called urushiol. This oil is found in all parts of the plant; leaves, stems, and roots. Even in extremely minute quantities, like a billionth of a gram, it can cause a very severe allergic reaction to our skin. This usually occurs within 24-36 hours after exposure.
Eighty five percent of our population is susceptible to this rash and a lucky fifteen percent have a natural resistance to it.
You can be exposed to the oil by direct contact with any part of the plant, or by indirect contact with an object such as your own hands, clothing, tools, or anything that may have the urushiol oil on it. There have also been reported cases of smoke from burning poison oak, causing either a skin rash or a reaction in the lungs, although I have never seen this in any patient I’ve treated.
Once you have contact with the oil you have only a matter of minutes to wash it off before it will bind to the skin and begin the allergic rash. The best way to remove the oil from the skin is to rinse with lots of water and then wash with soap and water. Most any kind of soap will do. Also, wash any object which may have come in contact with the oil with soap and water, including the clothes you were wearing. And don’t forget to do the same to your shoes, tools, and pets. Urushiol oil can remain active on inanimate objects for over a year.
There are a number of over the counter products including Technu and Zanfel, which are to be used on the skin after exposure to poison oak, to remove the oil. I have heard mixed reviews on their effectiveness. For now, I’ll stick with water and soap.
Poison oak rash never becomes systemic. It is medically called a “contact dermatitis,” and the only place where a rash can develop is where the urushiol oil has contacted the skin. Poison oak rash can affect almost any part of the body. The rash does not spread by touching it even if it is oozing a liquid, although it may seem to when it breaks out on new areas over a number of days. This may happen because the oil from the poison oak plant absorbs more slowly on thicker skin, such as the forearms, legs, or trunk and faster on thinner skin such as the face and genitals, making it seem like it is spreading.
Can poison oak rash be prevented before contact with the oil? Some allergy pills or shots have been used with limited success, but in general, they are no longer used, because of potentially serious side effects
A poison oak rash will always eventually clear up on its own if one is willing to wait it out. There are an abundance of home remedies to cure poison oak, none of which have been proven to be effective. However there is effective, proven, and safe medical treatment for those who wish not to suffer for several weeks. Your doctor may prescribe some form of a steroid cream which is stronger and much more effective than over-the-counter cortisone cream. If the rash is more serious and especially involving the face, systemic treatment may be necessary. This involves the use of cortisone pills called prednisone, which is my preferred treatment, or as a steroid shot. Either of these treatments is safe and very effective for most patients. Your doctor will help to determine the best treatment for your particular condition.
The bottom line is that you should avoid contact with poison oak, wash your skin and clothing as soon as possible if you do come in contact, and see your doctor for effective medical treatment if symptoms persist or worsen.
- Terry Hollenbeck, M.D., is a retired urgent care physician at Palo Alto Medical Foundation Santa Cruz in Scotts Valley. Readers can view previous columns on his website, valleydoctor.wordpress.com, or e-mail
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