Leaflets Three…Let It Be!

It appears that consistent warm weather has finally arrived in Indiana and people are finally able to get out to commune with nature. This will probably result in a lot of rashes showing up in doctors’ offices. Most of the rashes we see in the summer are caused by poison ivy, one of three plants in Indiana that are members of the genus Toxicodendron. This genus also includes poison sumac and poison oak.

The physical appearance of the poison ivy plant is highly variable, though it always has leaves in sets of three (see illustration). A memory aid from my Boy Scout days lets me recall what it looks like – “leaflets three let it be.” However, not all leaves of three are poison ivy, and other plants, like Virginia Creeper, can have a similar appearance.

The rash of poison ivy, like most contact rashes, is caused by the reaction of the immune system to the plant’s oil on the skin. When dealing with poison ivy, sumac or oak, it causes a typical rash, known as “rhus dermatitis.”

In the case of poison ivy, oak and sumac, the offending chemical is the plant resin urushiol. This resin can be found on any part of the plant, including the leaves, stems, roots, and berries. Even if the plant is dead, or the leaves have fallen off, urushiol can remain active for up to five years. Urushiol is also found in mangos and the shells of cashew nuts.

To develop rhus dermatitis, you must be sensitized to urushiol. This means you have to have had a prior exposure to the resin to activate your immune system. The typical rash then develops on subsequent exposures. Between 15 to 30 percent of people require numerous repeated exposures to urushiol before they have any reaction at all. It’s interesting to note that Native Americans, who have lived around these plants for centuries, react the least of any race.

The initial rash usually occurs 24 to 48 hours after exposure to urushiol. It appears as redness with blisters, usually found in a line where the plant brushed the skin. Areas of skin covered with clothing are generally spared unless the victim transfers the oil from clothing to skin that was covered (important health tip to males – if you’ve been handling plants, always wash your hands with soap and water before urinating).

People often have the misconception that fluid from the blisters can spread the rash. However, once the resin is washed off the skin with soap and water, the rash can no longer spread. People often wonder if it’s not contagious, why does the rash seem to spread? This depends on the amount of resin the skin is exposed to. If an area is exposed to a large amount of urushiol, it will break out sooner after contact. Areas that get a smaller dose may not break out for up to two weeks after the exposure. Someone might also be getting repeated exposures from clothing or tools they were using or even from pets that might have the resin on their fur. The entire course of the rash may last up to a month or so if left untreated.

Treatment of rhus dermatitis is based on the severity of the rash. If you know you have touched poison ivy, wash the area of contact immediately with lots of soap and warm water. Minor rashes usually respond well to cool compresses and either topical or oral diphenhydramine (Benadryl®). Over the counter 1% hydrocortisone cream applied three to four times a day can also speed resolution, though you should not use it around the eyes or mouth, areas of the body that have thin skin, and very sparingly on children.

More severe cases may require a trip to the doctor. We usually prescribe a steroid cream, ointment, or sometimes steroid pills. Pills are usually prescribed if the rash is found on the face or around the eyes. Occasionally scratching the rash may cause a secondary bacterial skin infection. If this happens your health care provider may also prescribe antibiotics.

As always, an ounce of prevention beats a trip to the doctor. Know what the plant looks like. When you’re in an area with possible poison ivy, wear long sleeves, pants, and gloves. Avoid rubbing your skin with clothing or gloves that have come into contact with vegetation. Take a hot soapy shower or bath as soon as possible. Wash your clothing in hot water as well.

– Dr. John Roberts is a retired member of the Franciscan Physician Network specializing in Family Medicine.