Poison Oak and Ivy

Summary
If you do nothing, it'll heal in two weeks. If you try all these over the counter and/or natural remedies, wait 14 days. If you go to the doctor for serious mind altering steroids, it's gone within a day.

What is it and how does it work?
Various species of the genus Rhus. The sap and crushed leaves contain a chemical which is absorbed by skin cells. The body mounts an immune response to these contaminated cells. Once begun, the reaction ends only when all the contaminated cells have been shed. This is one argument for scratching as much as possible, at the expense of additional scarring.

What are effective treatments?
There are a lot of conflicting suggestions for treatment. Antihistamines are either very effective or worthless. If the affected area is small enough, self treatment with over the counter remedies can provide "temporary relief." One cheap suggestion is to apply very hot (but not scalding) water to the area, which is supposed to provide several hours of relief by deadening the nerves in the area. One person reported losing a lot of skin with this method. Others report that the itching recurs worse than before, possibly due to increased blood flow in the area. I did not try this method.

Various over the counter remedies (rhuligel, caladryl, calamine lotion, benadryl) contain alcohol which appears to work by cooling and drying the area. This is reputed to cause cracking and even more itching. In my case, the itching returned very quickly. Hydrocortisone cream is supposed to be effective, although some people indicate that over the counter concentrations are too weak to be effective. I observed no response to over the counter hydrocortisone.

Symptoms may persist for up to two weeks after exposure. None of the above remedies will reduce this time.

For more serious or widespread cases, a doctor can prescribe steroids which apparently suppress the immune response to contaminated cells. Topical steroid creams are less effective, but may be preferable because they aren't systemic (absorbed) (some people warn that this is not true when used in the quantities required for a large affected area). Oral, systemic gluco-cortico-steroids may cause behavioral changes, but are effective and rapid (my symptoms disappeared within 24 hours).

How can I prevent this?
Learn to recognize and avoid the plant. If exposed, wash the affected area as quickly as possible with soap and cold water (hot water is reputed to cause the pores to open and allow the oak oil in). A product called Tecnu is supposed to break down the active ingredient in the oil. It's available at some drug stores, or from Solutions (1-800-342-9988). It's supposedly recommended by power company linemen. The oil is very easily spread, and can persist in crystalline form on clothing or other contacted items (including pets) for many months (years?), so you should wash anything you may have touched. Scratching affected areas after symptoms develop can not spread the infection, but different levels of exposure, and secondary exposures, can cause delayed reactions (2-3 days) in adjacent areas, giving the impression of spreading.

There are supposed to be naturopathic regimens to develop immunity to poison oak. Some people are naturally immune.

Under no circumstances should you burn the plant; the smoke is as potent as the plant itself. "Inhaling the smoke can produce a systemic reaction, including potentially serious lung inflammation."

References
Medicine for Mountaineering