Poison ivy rash is caused by contact with poison ivy, a plant that’s found on four continents. The sap of the poison ivy plant contains an oil called urushiol. This is the irritant that causes an allergic reaction and rash.

You don’t even have to come in direct contact with the plant to have a reaction. The oil can linger on your gardening equipment, golf clubs, or even your shoes. Brushing against the plant — or anything that’s touched it — can result in skin irritation, pain, and itching.

Here’s how to spot the danger, and what you can do if poison ivy gets too close.

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Even if you never saw the offending three-leafed culprit, the resulting rash is hard to ignore. This type of allergic reaction is known as contact dermatitis. It happens when your skin comes into contact with an irritant such as urushiol.

Poison ivy exposure can result in thin red lines on the skin when you’ve brushed against the edge of the leaves directly. If you touch pets that have the oil on their fur or touch clippings when emptying the mower bag, the rash can cover a larger area.

Classic symptoms that you’ve come into contact with poison ivy include:

The rash can take a few days to fully develop, and it may give the illusion of spreading.

If you’ve gotten a rash despite your best efforts to avoid the plant, there are things you can do. You can usually treat the rash yourself at home. However, you should go to the emergency room for urgent medical care if:

Most cases of poison ivy don’t need to be treated by a doctor. If you’ve come into contact with poison ivy, here’s what to do:

Wash your skin and clothes: Immediately wash skin that’s had contact with the plant. This may help remove some of the oil and lessen the severity of your reaction. Also, be sure to wash the clothes you were wearing, along with anything that may have touched the plant. Although the rash can’t spread, the oil that caused it can.

Take an antihistamine: Taking an over-the-counter antihistamine such as Benadryl can help relieve itching and allow you to sleep more comfortably.

Apply drying lotion: Apply calamine lotion or hydrocortisone cream topically to stop the itching.

Soothe your skin: Take frequent warm baths in water containing an oatmeal product, or apply cool wet compresses to help relieve the itch.

Don’t scratch: Scratching the rash will only make things worse. While it may bring immediate comfort, scratching will only prolong symptoms. You may even develop an infection if you break the skin, causing itching to intensify.

Poison ivy doesn’t have a cure, but even left untreated, it will eventually clear on its own.

Poison ivy is native to every state except California, Alaska, and Hawaii, and can be found in Central America, Mexico, and Canada as well. It’s been introduced to countries in Central America, Asia, and Europe, and is found in Australia and New Zealand too – so there’s a pretty good chance you’ll eventually cross paths with it. Learning how to identify poison ivy may help you avoid this highly irritating plant.

Poison ivy grows as a shrub in the northern and western United States, where the most commonly found type of poison ivy is known as western poison ivy. This type can grow to be anywhere from 6 to 30 inches tall. A second type, known as eastern poison ivy, grows as a trailing vine along the ground or clinging to trees in the East, Midwest, and South.

For both western and eastern poison ivy, the leaves are each made up of three-pointed leaf clusters, which have a glossy surface. This is where the old saying, “Leaves of three, let it be,” comes from. The edge of the leaflets can be toothed or smooth.

The leaves of the poison ivy plant are green in the summer, but can turn red, orange, or yellow in the spring and fall. The plant may flower with greenish-yellow blossoms and produce small, green berries that turn white in the fall.

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Urushiol, the irritating chemical compound that causes rash, can be found on all parts of the poison ivy plant, including the leaves, vines, stem, and roots.

An allergic reaction occurs when the oil comes in contact with your skin. Knowing what to look for is only part of the equation when it comes to avoiding the rash. The key is to prevent contact.

Prepare yourself before venturing into places where you might find the plant. This means covering your skin before gardening or doing other outdoor activities. You should also wear eye protection while mowing.

If you can’t cover your body completely, use an ivy blocking cream. There are several varieties that protect your skin from absorbing urushiol. They usually contain an ingredient called bentoquatam. Apply it before going outdoors. Pack a supply of ivy blocking cream to take along with you if you’re hiking or camping.

Carefully clean items that have touched with poison ivy to prevent exposure later. Gardening tools, sporting equipment, and camping supplies can all harbor urushiol.

A little prevention can go a long way. If you take precautions, you may never discover how uncomfortable the rash can be.