Poison Oak and Ivy

Poison Oak and Ivy are the single most common cause of allergic reactions in the United States and will affect ten to 50 million Americans every year. These plants grow practically everywhere in the United States, except Hawaii, Alaska and some desert areas of Nevada. Poison oak grows in the West and poison sumac and ivy in the South.

The rash is really an allergic contact dermatitis caused by a substance called urushiol, (you-ROO-shee-ol), found in the sap of poison ivy, 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 the stem and the leaves. You may develop a rash without ever coming into contact with poison oak, because the urushiol is so easily spread. Sticky and virtually invisible, it can be carried on the fur of animals, on garden tools, sports equipment, or on any objects that have come into contact with a crushed or broken plant. After exposure to air, urushiol turns brownish-black, making it easier to spot. It can be neutralized to an inactive state by water.

Once it touches the skin, the urushiol begins to penetrate in a matter of minutes. In those who are sensitive, a reaction will appear in the form of a line or streak of rash (sometimes resembling insect bites) within 12-48 hours; the rash can develop from 5 hours to 15 days after first time exposure to urushiol.

Redness and swelling will be followed by blisters and severe itching. In a few days, the blisters become crusted and begin to scale.

Without treatment, the rash usually lasts about 10 days to 3 weeks. But in people who are very sensitive to urushiol, the rash may take up to 6 weeks to heal.

The rash can affect almost any part of the body, especially areas where the skin is thin; the soles of the feet and palms of the hands are thicker and less susceptible.. The rash will continue to develop in new areas over several days but only on the parts of your skin that had contact with the urushiol or those parts where the urushiol was spread by touching. The rash may seem to be spreading, but either it is still developing from earlier contact or you have touched something that still has urushiol on it.

Sensitivity to poison oak is not something we are born with. It develops only after several encounters with the plants, and sometimes over many years. Studies have shown that approximately 85 percent of the population will develop an allergic reaction if exposed to poison oak. This sensitivity varies from person to person. Although they are not sure why, scientists believe that an individual’s sensitivity to poison oak changes with time and tends to decline with age. The first bout of poison oak usually occurs in children between the ages of 8 and 16, and can be quite severe. If there is no repeated exposure to poison oak, or urushiol, sensitivity will probably decrease by half by the time these individuals reach their thirties.

Investigators have found that people who reach adulthood without becoming sensitized have only a 50 percent chance of developing an allergy to poison oak. Those who were once allergic may lose their sensitivity later in life. However, you should not assume that you are one of the few people who are not sensitive– only 10 to 15 percent of the population is believed to be resistant. That same percentage (25-40 million people) is thought to be very susceptible to poison oak. These people will develop a rash and extreme swelling on the face, arms and genitals. In such severe cases, treatment by a dermatologist will be required.

Identify poison ivy, poison oak and poison sumac. Learn what the plants and leaves look like and where they’re commonly found so that you can avoid them. The popular saying “leaves of three, let them be,” is a good rule of thumb, but it’s only partially correct. Poison oak or poison ivy will take on a different appearance depending on the environment. Although poison oak is usually a summer complaint, cases are sometimes reported in winter, when the sticks may be used for firewood, and the vines for Christmas wreaths. Poison oak is found in the West and Southwest, poison ivy usually grows east of the Rockies, and poison sumac east of the Mississippi River.


Take precautions outdoors. When hiking try to stay on cleared pathways. Keep pets from running through wooded areas so that urushiol doesn’t accidentally stick to their fur, which you then may touch. If you think your pet may have run through poison ivy, oak or sumac, put on some long rubber gloves and give your pet a bath to remove any residual urushiol.

Remove poison ivy. In your backyard, you can use an herbicide to get rid of poison ivy or use heavy gloves to carefully pull it out of the ground. Note that even dead plants can cause a reaction. Afterward, remove and wash your gloves and hands thoroughly. Don’t burn poison ivy or related plants because the urushiol can be carried by the smoke and cause irritation or injury.

Clean anything that may be contaminated. Wearing long pants, socks, shoes and gloves will help protect your skin, but be sure to wash your clothing promptly with detergent — in a washing machine, — if you think you’ve come contact with poison ivy. Handle contaminated clothes carefully so that you don’t transfer the urushiol to furniture, rugs or appliances. In addition, wash any other contaminated items, such as outdoor gear, garden tools, jewelry, shoes and even shoelaces, as soon as possible. Wash your skin with soap and water. Gently washing off the harmful resin from your skin, using any type of soak, within five to 10 minutes after exposure may help avert a reaction. After an hour or so, however, the urushiol has usually penetrated the skin and washing won’t necessarily prevent a reaction, but it may help reduce its severity. Be sure to wash under your fingernails too.

Apply a barrier cream. Apply an over-the-counter barrier skin cream containing bentoquatam (Ivy Block) to protect your skin. Bentoquatam absorbs urushiol and prevents or lessens your skin’s reaction to the oil.


Initial treatment consists of washing the area with water immediately after contact with the plants. To relieve symptoms, use wet compresses and take cool baths. Over the counter and prescription creams and antihistamines may help relieve symptoms. Moderate or severe cases may require steroid pills.

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