Even airborne contact is possible, especially in the fall or winter when these poisonous plants are burned among other brush, and particles of urushiol are released into the air. If the airborne particles land on your skin or you inhale them, you can get a widespread rash and severe irritation in the respiratory tract.
The rash, which presents like itchy red patches, often accompanied by blisters arranged in streaks, typically surfaces [within hours] to four days after exposure. It doesn't always come on at the same time. People often mistakenly assume a new rash means they were exposed again.
Many people who are allergic to poison ivy are also allergic to oil from cashew nut tree shells, the skin of mangoes, and the black sap of the Japanese lacquer tree. Polymerized urushiol can persist in lacquered furniture and cause allergies for hundreds of years.
How should you treat plant allergies?
That depends on the plant and the reaction.
In the case of cacti or other spiny plants, the spine should be carefully removed from the skin, usually with tweezers. If it's a really small spine or glochid, apply glue and gauze to the site, allow it to dry, and peel it off.
Minor itching, irritation, or rash can be typically treated with an oral antihistamine or over-the-counter topical steroid. But if a rash doesn’t respond to over-the-counter treatments, you should see a dermatologist. In cases where a rash is accompanied by more severe reactions such as difficulty in breathing or swallowing, go to the emergency room immediately.
If you come in contact with poison ivy, rinse the skin with water immediately. About 50% of the urushiol will come off if you rinse within 10 minutes. But avoid soap; it can spread the resin.
Lukewarm baths and soaks with products containing aluminum acetate (a type of salt that dries up the blisters and any weeping) and topical preparations such as calamine or topical steroids are helpful in treating a poison ivy rash.
In cases in which a rash is severe or covers a large area of the body, a dermatologist may prescribe strong topical steroids or a two- to three-week course of oral steroids.