Brush up against poison ivy leaves, and almost 90% of adults will develop an angry, red rash. Unsuspecting hikers, gardeners and campers regularly come across the plant in warmer months, but it’s also possible to encounter the toxin indirectly, like via your dog’s fur.

Growing as both a shrub and a vine, the innocuous-looking flora produces a noxious sap responsible for the reaction, called allergic contact dermatitis. Both poison ivy and oak sprout leaves with three leaflets, and sometimes include berries.

Urushiol — the clear liquid on top — can cause a painful and irritating rash on your skin, including oozing blisters. The violent outbreak may appear as long as three days after exposure, according Dr. Rajani Katta, M.D., a dermatologist based in Bellaire, Texas, who specializes in contact dermatitis.

Attack the rash at first sign with a steroid cream like hydrocortisone. “Steroids target the immune system’s response in the skin and shut off the molecules that trigger inflammation,” Katta says.

For itch relief, don’t discount an old-fashioned oatmeal bath. While it won’t reduce redness, a long soak can reduce the urge to scratch. “Substances in the oatmeal bind to the skin and form a protective barrier,” Katta explains. “They also hold moisture in and provide a soothing effect.”

If the rash doesn’t subside within a few days — or it covers your entire body — skip over-the-counter cream entirely and head straight to the doctor. Severe cases require immediate medical attention and prescription-strength hydrocortisone to calm the reaction.

A growing breakout, however, doesn’t mean you’re contagious. Lingering oils cause the blisters to “spread” to new places, or even other people. Urushiol remains potent for weeks at a time, so you should always wash your skin with soap and water immediately after coming into contact with it.

Don’t neglect other surfaces too. Start by cleaning your gardening tools, steering wheel, carpet or wherever else the residue might hide. And yes, that includes giving your dog a bath too!