Poisonous plants cause the most common allergic reactions to the skin, affecting as many as 50 million Americans each year, according to the American Skin Association. University of Alabama at Birmingham Associate Professor of Emergency Medicine Dr. Walter Schrading says it is important that people are able to identify poisonous plants, prevent an allergic reaction and treat skin irritations after contact.

The three most common types are poison ivy, poison oak and poison sumac. All three produce the resin called urushiol, which helps the plant retain water. The colorless resin on the stems and leaves causes toxic effects within 24-48 hours of contact with skin.

Poison ivy is a three-leaf plant found on the East Coast in moist, shady areas. It is a vine that often grows up trees.

Similarly, poison oak is a three-leaf plant found on the West Coast and in some Southern states, growing in shrubs. The vine-like plant may have clusters of green-yellow or white berries.

Poison sumac is found in wet, marshy regions around riverbanks and looks like a small tree or shrub, sometimes growing 15 feet tall or more. The stem has seven to 13 smooth, oval leaves that are arranged in pairs.

“The adage, ‘Leaves of three, let me be,’ is a good one stick by,” Schrading said. “When working in the yard or exploring outdoors, it is important to be aware of your surroundings and the plants that you come in contact with.”

Virginia creeper is often mistaken for poison ivy. The imposter plant looks like poison ivy, but has five leaves. Often, the two plants grow together. Although it is not as allergenic as poison ivy, the sap of Virginia creeper can cause skin irritation and blisters in sensitive people when it punctures the skin.

Preventing an allergic reaction

Poisonous plants are a common cause for skin rashes. Urushiol is on the s plants year-round, even when they are brown and not fully grown. Precaution should be taken even in the fall and winter months.

“Prevention is key when you are outdoors,” Schrading said. “If you are in an area that contains weeds or overgrowth, it is best to take precautions to protect your skin from interacting with the resin that comes off the plants.”

A few precautions to take:

• When outdoors in wooded areas, wear long pants and long-sleeve shirts to avoid contact with poisonous plants.
• If you are gardening and suspect poisonous plants in the area, use gloves to extract the plants.
• Use Ivy Block, an over-the-counter topical containing Bentoquatam, which protects skin from urushiol. It should be applied every four hours.

Contact dermatitis

The severity of a rash will depend on the person and his or her allergic reaction. Some people have a genetic predisposition to an extreme reaction.

Contact dermatitis is the skin rash caused from exposure to poisonous plants. It is a red, linear rash that burns or itches and, oddly enough, some symptoms may not occur until 10-14 days after contact. Severe symptoms include small bubbles on the skin, swelling around the contact dermatitis, skin leaks and skin crusts.

Typically, the legs and arms come in contact with urushiol. The rash can spread to areas that may not have been exposed due to touching the plant, when the person touches or scratches the ears, nose, etc. If the resin is on clothing, it can be transferred by contact with skin.

Pets can  transfer the resin from a plant to humans. It rarely affects pets because their fur is a protective barrier.

“If a dog brushes up against a plant, then you pet the dog, you come in contact with urushiol and could have an allergic reaction,” Schrading said. “If you have an unexplained rash, this could be the culprit.”

Treatment for skin contacted by urushiol

More than 85 percent of people will have an allergic reaction when their skin comes in contact with urushiol. Ten to 15 percent of those people will have a severe reaction.

“When people have contact dermatitis, they tend to scratch the rash, damaging the skin. This becomes a vicious cycle and keeps the skin from healing fully,” Schrading explained.

If you suspect that you have come in contact with a poisonous plant, rinse the area with soap and water or rubbing alcohol as quickly as possible. If using rubbing alcohol on children, use sparingly.

Once you have contact dermatitis, it will take one to two weeks at a minimum to heal. Here are a few options for treatment at home:

• Use a topical cortisol steroid like hydrocortisone, available over the counter, to treat the rash.
• Calamine lotion serves as a soothing agent and promotes drying of the skin to heal the rash.
• Aluminum acetate paired with a cool compress provides relief during the blistering stage.
• Soaking for 15-20 minutes in an oatmeal bath can soothe the itching.
• If the allergic reaction spreads to a lot of the body and swelling of the face and eyes is experienced, a physician can prescribe an oral steroid to promote healing. Seek medical treatment if the allergic reaction is on the face, as cortisol may not be safe to put on the face.