DOVER — While walking in the woods or doing yard work, Delawareans face the potential to encounter one of three poisonous plants that cause unpleasant allergic reactions.

The three plants are poison ivy, poison oak and poison sumac; all members of the cashew family and native to Delaware. Each of the plants contain urushiol, a rash-causing colorless, odorless oil.

According to the Delaware Department of Natural Resources and Environmental Control’s botanists, poison oak is a low-growing deciduous shrub growing mainly in Sussex County where it thrives in dry, sandy soils. Poison oak has leaves in groups of three with hair along the veins of the leaves. The plant may also have yellow or white berries.

Poison sumac is a short, deciduous tree, a rare species in Delaware but it can be found growing in forested wetlands in all three counties. It can be identified by its reddish leaves that come in clusters of seven to 13. It also has greenish flowers and bears small white fruit.

Poison ivy is a woody vine common and widespread throughout the state, growing in a variety of habitat types. It’s leaves come in clusters of three with white berries and a furry vine. Poison ivy is the species residents are most likely be encounter.

Since all three poisonous plants can be found in Delaware, it’s important to take precautions to prevent contact with their oils.

Dr. Paul Pulchny of Bayhealth Family Medical and Internal Medicine in Harrington said the best way to reduce your chances of exposure to urushiol is to wear long pants and long sleeves when in wooded areas and gloves when working in brush.

“Many people think just covering up is enough but they have to take into consideration that the oil can stay on clothes too,” Dr. Pulchny said.

For that reason, he recommends carefully taking off clothes before putting them straight in the washer and showering before putting fresh clothes on. A rash can be caused by indirect contact, like contaminated clothes rubbing on the skin. Other indirect ways to become infected include from pet fur or garden tools that have been exposed.

About 50 percent of the population is immune to the effects of urushiol but for those who aren’t, exposure can trigger the body’s histamine response, causing an itchy, red rash which may also include bumps and blisters. The liquid inside blisters will not spread the rash if the blister bursts.

Dr. Pulchny said reactions to urushiol can be treated at home with Benadryl cream, Cortizone 10 cream or Calamine lotion, all of which will help reduce the itch. But the duration of the rash could be up to three weeks.

In many cases, the rash my appear to be spreading over the first few hours or couple days, but it can be attributed to different exposure times or varying absorption rates on different areas of the body.

Although most cases do not require a doctor’s visit, cases with excessive blistering, pain instead of itchiness, spreading of the rash for a week or more, or open wounds indicate a visit to a physician may be necessary.

“The most common reason people come into the office for poison ivy is from scratching the rash too much,” Dr. Pulchny said.

Scratching too much can break the skin and cause an infection.

To cure the infection or improve unbearable itchiness, doctors may prescribe oral or cream steroids.

Although poison oak, sumac and ivy may seem useless, they remain important to animals. DNREC reports that all three species are a food source for migratory and wintering songbirds such as the yellow-rumped warbler.