How does poison oak cause rashes?
Poison oak is best known for containing “poison” - or, to be more accurate, an oil called “urushiol” which causes an allergic reaction if it is absorbed by the skin. Although not everyone who comes into contact with poison oak will experience such a reaction, around 85% of people will. Urushiol-induced contact dermatitis is common, and most people are familiar with the symptoms: a bumpy red rash, inflamed or swollen areas, blisters, burning sensations, and unbearable itching.
Urushiol oil is present in the leaves, roots, and stems of poison oak, and is very easily transferred by even the lightest brush against the plant. It will rub off on whatever has made contact with the plant, whether that's clothing, skin, even the fur of an inquisitive pet! Whether your skin receives its dose of urushiol directly from the poison oak, or from touching affected clothing or objects, the effect will be the same. Many people are unaware that you don't actually need to touch poison oak to experience the effects! It's not the plant that causes the allergic reaction – it's the oil. And you can pick that up from other sources, not just the plant. If not immediately washed off, the oil will bind to the skin and quickly be absorbed. Once this happens, the rash will follow within 36 to 48 hours – it's not possible to wash it off once it's been absorbed by your skin.
You can't catch poison oak from someone else who already has the rash: this is a common misconception. As long as sufferers have washed since coming into contact with poison oak, they are not contagious, because the rash is caused by urushiol oil, nothing else. Once the oil has been absorbed by the skin, and none remains on the surface, it can't be transferred. For this reason, it's important to wash thoroughly as soon as you realize that you've been in contact with poison oak, even if you don't have any visible symptoms yet. Firstly, you could prevent the rash from ever appearing, if you haven't touched your skin (thus rubbing in the oil) and have washed the oil off immediately, before any got the chance to soak in. Secondly, even if the damage is done and some of the oil has been absorbed, you can stop it being spread further or being more severe by washing off whatever urushiol remains on the surface of the skin. If you don't, the oil will continue to soak in and bring about a more severe rash. Not only that, but you'll most likely spread it around to other parts of your body through touch, and transfer it to everything you touch, too, meaning other people will probably pick it up at some point!
Because the oil that causes the poison oak rash remains active even on inanimate objects, you need to be really thorough in washing everything that might have been contaminated. Pets are often guilty culprits, carrying urushiol on their fur to their unsuspecting owners. Wash them if you think this is happening! And try to find the source and get rid of the poison oak, too.
Return to Poison Oak Guide Home Page