Poison ivy rash is caused by an allergic reaction to an oily resin called urushiol (u-ROO-she-ol). This oil is in the leaves, stems and roots of poison ivy, poison oak and poison sumac.

Wash your skin right away if you come into contact with this oil, unless you know you’re not sensitive to it. Washing off the oil may reduce your chances of getting a poison ivy rash. If you develop a rash, it can be very itchy and last for weeks.

You can treat mild cases of poison ivy rash at home with soothing lotions and cool baths. You may need prescription medication for a rash that’s severe or widespread — especially if it’s on your face or genitals.

Signs and symptoms of a poison ivy rash include:

Poison ivy rash often appears in a straight line because of the way the plant brushes against your skin. But if you develop a rash after touching a piece of clothing or pet fur that has urushiol on it, the rash may be more spread out. You can also transfer the oil to other parts of your body with your fingers. The reaction usually develops 12 to 48 hours after exposure and lasts two to three weeks.

The severity of the rash depends on the amount of urushiol that gets on your skin.

When to see a doctor

Seek emergency medical attention if:

See your doctor if:

Poison ivy rash is caused by an allergic reaction to an oily resin called urushiol. It’s found in poison ivy, poison oak and poison sumac. This oily resin is very sticky, so it easily attaches to your skin, clothing, tools, equipment and pet’s fur. You can get a poison ivy reaction from:

Pus that oozes from blisters doesn’t contain urushiol and won’t spread the rash. But it’s possible to get poison ivy rash from someone if you touch plant resin that’s still on the person or contaminated clothing.

Your risk of a rash is increased if you participate in outdoor activities that put you at higher risk of exposure to poison ivy, poison oak and poison sumac:

If you scratch a poison ivy rash, bacteria under your fingernails may cause the skin to become infected. See your doctor if pus starts oozing from the blisters. Your doctor might prescribe antibiotics. Serious difficulty breathing and inflammation of the lining of the lungs may result from inhaling urushiol.

To prevent poison ivy rash, follow these tips:

You generally won’t need to see your doctor to be diagnosed with a poison ivy rash. If you go to a clinic, your doctor will likely diagnose your rash by looking at it. You usually won’t need further testing.

Poison ivy treatments usually involve self-care methods at home. And the rash typically goes away on its own in two to three weeks.

If the rash is widespread or causes many blisters, your doctor may prescribe an oral corticosteroid, such as prednisone, to reduce swelling. If a bacterial infection has developed at the rash site, your doctor might prescribe an oral antibiotic.

A poison ivy rash will eventually go away on its own. But the itching can be hard to deal with and make it difficult to sleep. If you scratch your blisters, they may become infected. Here are some steps you can take to help control the itching:

You probably won’t need medical treatment for a poison ivy rash unless it spreads widely, persists for more than a few weeks or becomes infected. If you’re concerned, you’ll probably first see your primary care doctor. He or she might refer you to a doctor who specializes in skin disorders (dermatologist).

What you can do

Before your appointment, you may want to list all the medications, supplements and vitamins you take. Also, list questions you’d like to ask your doctor about your poison ivy rash. Examples include:

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

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