Poison ivy rash is allergic contact dermatitis caused by a substance called urushiol, found in the sap of poison ivy. This same substance can be found in other plants as well, notably poison oak, and poison sumac.
Urushiol is a colorless, or slightly yellow oil that oozes from any cut, or crushed, part of the plant, including both stem and leaves. Simply brushing against a plant may not cause a reaction. On the other hand, you may develop dermatitis without ever coming into contact with poison ivy, because the urushiol is so easily spread.
Sticky, and virtually invisible, it can be carried on the fur of animals, on garden tools, golf balls, or on any objects that have come into contact with a broken plant.
After exposure to air, urushiol turns a brownish-black, making it easier to spot, and is neutralized to an inactive state by water.
Once it touches the skin, the urushiol begins to penetrate in a matter of minutes. In those individuals who are sensitive to the chemical, reaction will appear in the form of a linear rash (sometimes resembling insect bites) within 12 to 48 hours. Redness and swelling will be followed by blisters and severe itching.
In a few days, the blisters become crusted and begin to scale. The dermatitis will usually take about ten days to heal, sometimes leaving small pigmented spots, especially in dark skin. The rash can affect any part of the body, especially areas where the skin is thinner and more sensitive to the ivy sap. The soles of the feet and the palms of the hands are thicker and less susceptible.
Prevention is the best cure. The best way to avoid the misery of poison ivy dermatitis is to be on the look-out for it, and stay away. In the backyard, the weed can be destroyed by herbicides, but this is not a working solution for forest preserves or natural sites. It is best to wear long pants and long sleeves, and, if practical, gloves and boots.
Be aware that the plant's almost invisible and oily resin sticks to almost any surface, and can even be carried in the wind or in smoke when it is burned, and inhaled.
Standard barrier creams offer little hope against rampant poison ivy and poison oak.
If you think that you have had a brush with poison ivy, wash all exposed areas with cold, running water as soon as you can reach a stream, lake, or garden hose. If you can do this within five minutes, the water will neutralize, or deactivate, the urushiol in the plant's sap and keep it from spreading to other parts of the body. Soap is not necessary, and may even spread the oil.
If you know that you have a severe response to urushiol, wash the affected areas with Tecnu as soon as you get home. Also when you return home, wash all clothing outside with a garden hose before bringing it into the house, where resin could be transferred to rugs or to furniture. Handle the clothing as little as possible until it is soaked.
Since urushiol can remain active for months, it is important to wash all camping, hiking or hunting gear that may also be carrying the resin.
If you come down with a rash, avoid scratching the blisters. The fluid in the blisters will not spread the dermatitis. Rash that develops after the initial rash is most likely due to lesser levels of exposure of that particular area of the skin during the initial exposure. However, fingernails may carry germs that could cause an infection in the areas where skin is inflamed due to the poison ivy.
Cool showers will help ease the itching and simple, over-the-counter preparations, like calamine lotion or Burrow's solution, will relieve mild rashes. Soaking in a tepid bath with an oatmeal or baking soda solution is often recommended to dry oozing blisters and offer some comfort.
A hot bath or shower often produces relief in that heat releases histamine, the substance in the skin that causes intense itching. Therefore, a hot shower will cause intense itching as the histamine is being released. The heat should be gradually increased to the maximum tolerable and continued until the itching subsides. This process will deplete the cells of histamine, and the patient will obtain up to 8 hours of relief from itching.
In severe cases, corticosteroid drugs can halt the reaction if given soon enough. A doctor may prescribe a steroid cream stronger than 0.5 percent hydrocortisone to be applied to the lesions four to six times a day. An alternative is to use steroid (such as prednisone) pills for short periods of time. The itching may also be treated systemically with either an antihistamine or aspirin.