Poison Ivy, Poison Oak, and Poison Sumac

The itching and the rash associated with poison ivy, oak, or sumac are immune-system reactions that result from either touching the plants directly or coming in contact with clothing, garden tools, or pets that have been exposed to the plants (which are scattered around most of the United States and Canada).

Signs of a Reaction to Poison Ivy, Poison Oak & Poison Sumac

A red, bumpy, itching rash will develop at the site of exposure. Often the rash is followed by small blisters and localized swelling of the skin. About 85 percent of the population will develop symptoms, which may take one to two weeks to develop on first contact. After any subsequent exposure, a rash can appear after only two or three days.

The source of this allergic reaction is urushiol (you-ROO-she-all), a colorless or sometimes slightly yellow oil that occurs in the sap of the plant genus Rhus. Poison ivy, oak, and sumac all belong to this genus (cashews and mangos are close relatives).

Just one billionth of a gram of urushiol is enough to make allergic people itch incessantly. The chemical is also very durable—if you don’t wash it off clothing, shoes, or tools, it will still be there many months hence and can cause a reaction.

Immediate Care for Poison Ivy, Poison Oak & Poison Sumac

Sensitivity to poison ivy varies from person to person, with individual sensitivity diminishing as one gets older (though at any age the first bout of poison ivy can be quite severe). Once contracted, poison ivy rash, blisters, and itch will normally disappear in 14 to 20 days without any treatment. But most people will need relief from the intense itch; some may require prescription medication.

If you think you have come in contact with any of the poison plants, here’s what to do.

  • Wash your exposed skin immediately. Wash with soap and lots of water within 5 to 10 minutes if possible. The longer you wait, the less effective washing becomes. If you’re out in the woods, use water from a lake or stream, or even beer from a picnic basket if you have any.
  • Apply rubbing alcohol. This inactivates any remaining urushiol. Don’t use a washcloth; this can spread urushiol. Instead, dab your skin with alcohol-soaked cotton balls.
  • Clean your clothing and anything else exposed to the plants. Urushiol can spread from clothing to you, so be extremely careful when undressing. Wear rubber gloves while handling clothes and other items, and then discard the gloves. Wash the contaminated clothes (separately from other clothes) in strong detergent. Shoes, tools, and other items that may have been in contact with urushiol need to be wiped off with alcohol and water.
  • Try not to scratch. Scratching can lead to infection. However, contrary to popular myth, scratching the rash (and breaking the blisters) won’t cause the rash to spread, since the water inside the blisters does not contain urushiol. In fact, once the rash appears, the urushiol is gone from that area—which is why the rash won’t spread elsewhere on you or from you to someone who might come in contact with it.
  • Try calamine lotion. For mild cases that afflict small areas, this popular lotion cools the skin and causes the blood vessels to constrict. The lotion leaves a powdery residue that absorbs the oozing and develops a crust that keeps it from sticking to your clothing. Apply it to the itchy areas every three to four hours. Discontinue after the oozing stops.
  • Nonprescription creams can also help. For mild itching, 1 percent cortisone creams—twice the strength of the old 0.5 percent formulations—can provide relief. However, over-the-counter cortisone creams won’t help if you have severe itching.
  • Have a milk soak. A compress with cold milk helps dry the rash and soothe the itch. Just soak milk in gauze and apply to your skin for 5 to 10 minutes.
  • Soak in the tub. A tepid tub bath, two to six times daily, with colloidal oatmeal (Aveeno) added, may be soothing. Since the oatmeal makes the tub slick, be sure to have a nonskid bath mat in place.
  • Rub on baking soda. If your rash is weeping or blistering, make a paste of water and baking soda and apply it to your skin. This helps dry up the oozing blisters.
  • Ice it. The cheapest remedy for the itch of poison ivy is to apply an ice cube to the affected area for about a minute. If you don’t have an ice cube, run cold water over the area.

Prevention Tips for Poison Ivy, Poison Oak & Poison Sumac

Poison Ivy Image - iStockphoto

Being able to recognize these poisonous plants is the key to avoiding them and the rash that they trigger. The old adage “Leaflets three, let it be” is accurate. But the poisonous plants vary tremendously—which is why many people don’t recognize them and end up in misery each year.

They can grow as woody vines or shrubs. The leaves can be dull or glossy, from one to five inches long, and have edges that are saw-toothed, lobed, or smooth. Though usually green, in autumn they can turn yellow; in spring they often bear small green or white flowers that mature into berries in late summer.

Poison ivy grows in every state but California, which is where one type of poison oak is concentrated. Another type of poison oak grows in the southeastern states. In damp areas like swamps or bogs, you may encounter poison sumac, a small tree or shrub related to poison ivy that has seven to eight leaflets on each stem.

Dress for the occasion. If you hike in woods known to have the itch-causing plants, wear gloves as well as clothing that will cover your arms and legs.

Buy protection. To help prevent another attack, an effective Food and Drug Administration (FDA) approved lotion is available over the counter that protects against poison ivy. Applied at least 15 minutes before exposure to poison ivy, Ivy Block (bentoquatam), which is sold in most pharmacies, binds to the urushiol and prevents it from being absorbed through the skin, or at least reduces a rash’s severity. Ivy Block has not been tested on children under six, but it may be useful for those who work and play outdoors and can’t avoid the poison plants.

Bathe your pet. Animals pick up plant secretions on their fur and bring it home. Wash your cat or dog (carefully, wearing gloves) if you suspect that the animal has been through poison ivy.

When to Seek Medical Help for Poison Ivy, Poison Oak & Poison Sumac

Contact your physician if symptoms grow worse, if the rash spreads to your mouth, eyes, or genitals, if it covers more than 20 percent of your body, or if you have had severe reactions to poison ivy (or poison oak or sumac) in the past.

To control the rash and itching, your physician will probably prescribe a topical corticosteroid or an oral antihistamine, or both. If your face, hands, or an extensive area of your body is afflicted, oral steroidal medication will be prescribed.

For More Information about Poison Ivy, Poison Oak & Poison Sumac

  • American Academy of Dermatology


The Complete Home Wellness Handbook

John Edward Swartzberg, M.D., F.A.C.P., Sheldon Margen, M.D., and the editors of the UC Berkeley Wellness Letter

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at HealthCommunities.com

Published: 03 Aug 2010

Last Modified: 12 Feb 2015