While this perennial flowering plant found in Ontario serves an extensive list of medicinal purposes, a simple brush against one of its leaves could mean a painful, itchy, and burning rash. 

Stinging nettle (Urtica dioica) is native to Europe, Asia, and western North Africa, although it can now be found growing in large masses in old pastures, flood plains, woodland areas, and along stream banks throughout Ontario. 

In medieval Europe, the plant was used as a diuretic (to rid the body of excess water) and to treat joint pain. Today, the plant is still used to treat some urinary issues, hay fever (allergic rhinitis), or in compresses or creams for treating joint pain, sprains and strains, and tendonitis. 

Despite its benefits, the plant is best known for being covered in tiny hollow hairs called trichomes that detach from the plant when you brush against it and act as "tiny needles that inject chemicals into your skin," causing painful stinging sensations. 

Photo: Haluk Cigsar/Shutterstock. 

While reddening and intense itching is common after contact, sensitive people may experience increased swelling and burning. A prolonged tingling sensation may also persist on the affected skin for more than 12 hours after exposure.

The plant can be distinguished by its dark green, jagged egg or heart-shaped leaves that grow in pairs on opposite sides of the stem.

The plant typically grows to about one metre in height and produces small hanging clusters of greenish-white flowers from June to September. 

If you're going to be spending lots of time outdoors, the provincial government recommends becoming familiar with hazardous plants, including the stinging nettle, to properly identify them by sight and avoid contact. Never touch or brush up against the plant with bare skin, and cover your body whenever possible. 

If you do develop a rash, avoid scratching, touching, or rubbing the affected skin, as this can irritate it even more.

You can wash the rash with soap and water or use other at-home remedies to calm your symptoms, including mixing baking soda with water and applying it to the area or using a cool compress or ice.