They’re best avoided, as these plants can leave you with an uncomfortable allergic skin reaction. Urushiol, an oil made up of toxic compounds, is found in these three plants and results in the itchy, painful skin rash that occurs after touching them.

“If someone is living from Maine to Florida and west to Texas and there’s a poisonous plant growing near their house, it’s poison ivy, because poison oak isn’t growing near someone’s home in that area,” Pennsylvania-based poison ivy horticulturist Umar Mycka told AccuWeather.

Being able to identify poison ivy (above), poison sumac and poison oak can help you avoid an itchy allergic skin reaction. (Photo/poison-ivy.org)

In Western states including Washington, Oregon and California, people are more likely to spot poison oak, according to Mycka. Although poison sumac is rare, it grows primarily in very wet conditions in the eastern portion of the United States.

“It doesn’t grow next to somebody’s house in a suburban lot because there’s not enough water for it to grow,” Mycka said.

How to identify these plants

A key step in avoiding contact with poison ivy, poison oak or poison sumac is knowing what they look like.

Poison ivy follows the rule of “leaves of three, let it be.” Their leaves tend to grow left and right but never side by side, according to poison-ivy.org.

“What confuses people is that when they look at a plant, it looks like almost every plant has three leaves,” Mycka said.

He recommended using the amended phrase “leaves of three resemble me” to help figure out if the plant you’ve come across is poison ivy.

“In this upgrade, we’re using our bodies as a template to see what those three leaves might look like,” he said.

The three leaves are a person’s head and two arms, according to Mycka. “Look at that plant and ask yourself, ‘Does it have a head? Is that head connected to a neck? Is that neck connected to another long stem, which is like a body?’ And connected to that stem are two other leaves that look like arms,” Mycka said. “That’s the main identifying factor of poison ivy.”

Other factors include plant and leaf size and color. Poison ivy leaves can appear as glossy green, but have a pink tinge in spring and turn orange in the fall, according to The Old Farmer’s Almanac.

“Some poison ivy plants have symmetrical leaves, but more often than not, they remind me of a mitten with a thumb on one side, making the leaf irregular,” said Leslie Elia, a certified health coach for nutritional health coaching company, Growing Vital Health. Elia and her son are severely allergic to poison ivy, she said.

“I’ve also noticed that the vein of the plant can be red, even though the stem and leaves are green,” Elia added.

You might see poison ivy growing as an erect shrub, along the ground or as a winding vine, and it commonly grows along roads or around fences. Leaves are usually shiny on younger plants and a duller green on mature plants.

5 ways seasonal allergies can irritate your skin

These signs indicate a serious sunburn that requires medical attention

How to keep your plants from wilting in the summer heat

Atlantic poison oak can grow up to 3 feet tall as a low-growing, upright shrub that sometimes looks like a vine, according to The Old Farmer’s Almanac. Pacific poison oak sometimes gets confused with poison ivy because it can grow as either a shrub or a vine.

Poison oak leaves look like oak leaves, though they’re not in the oak family, and the distinctly lobed or toothed leaflets are a duller shade than those of poison ivy. It can grow tan-colored fruit, called drupes.

Poison sumac can cause a more serious allergic reaction than poison ivy and poison oak, according to the University of Florida. Typically found in swamps or other wetlands, the woody shrub or small tree can reach heights of up to 20 feet.

Its leaves don’t follow the rule of “leaves of three, let it be.” Poison sumac leaves can have between seven to 13 leaflets arranged in pairs, with a single leaflet at the end of the midrib, according to the University of Florida.

They tend to have reddish stems and petioles, and leaflets are oval and elongated with smooth edges. They’re usually between 2 to 4 inches long and up to 2 inches wide with a velvety, smooth texture. Poison sumac leaves appear bright orange in spring, later becoming dark green and glossy on the leaf’s upper surface and pale green on the bottom.

How to treat allergic skin reactions

If you’re unfortunate enough to come into contact with any of these plants, consider the following tips: