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Hazardous plants that can cause painful skin reactions from inadvertent exposure by skin contact can be found throughout Ontario. Many people are familiar with poison ivy, but may not be aware of some of the more toxic plants including giant hogweed and wild parsnip. Exposure to the sap of the giant hogweed and wild parsnip can cause more serious skin reactions and result in long lasting scars compared to the other hazardous plants mentioned below. Workers who work in certain outdoor areas are at risk of exposure, and should become familiar with these plants to protect themselves.
Outdoor workers who may be exposed where these hazardous plants grow include construction workers, road crews, emergency response workers, forestry workers, loggers, farmers, camp counsellors, land surveyors, mining exploration crews, tree planters, landscape workers, fishing and hunting guides and parks and wild life management workers.
Hazardous plants in Ontario include giant hogweed, wild parsnip, poison ivy, poison sumac and stinging nettle.
Giant hogweed has a scattered distribution across southern and central Ontario. Contact with giant hogweed sap can cause blindness, severe blistering and burns on your skin.
Giant hogweed is a large plant, growing up to five metres tall. Young plants form large rosettes up to two metres high with no flowers. Mature plants send up flowering stems that produce large, white umbrella-shaped flower clusters up to 90 centimetres wide. There are two really distinguishing things about giant hogweed. First is its stalk which has reddish purple blotches and speckles and coarse hairs. Second, the leaves have unusual toothed edges like a jagged-looking maple leaf. In early May, leaves are about 30 centimeters in diameter. The plant contains a clear, watery sap that is a photosensitizer, which sensitizes skin to ultraviolet light like sunlight. Skin contact with the sap in combination with exposure to sunlight can cause swelling, severe burns and painful blisters, usually within 48 hours. The severity of skin reaction depends on individual sensitivity. Depending on individual sensitivity, effects can last for months and skin can remain sensitive to sunlight for years. Eye contact with the sap has been reported to cause temporary or permanent blindness.
Wild parsnip can be found throughout Ontario and is particularly abundant in eastern Ontario. It grows in abandoned yards, waste places, meadows, old fields, roadsides and railway embankments. Skin contact with the sap – also a photosensitizer – has similar effects to giant hogweed.
In its first year, wild parsnip grows close to the ground in the form of rosettes with leaves averaging six inches long. Mature wild parsnip have flower stalks that grow to about four feet tall and umbrella-like clusters of yellow flowers that form large flat seeds. Handling the fruit, flowers or leaves of wild parsnip followed by exposure to sunlight can cause inflammation of the skin. Skin reactions may range from burning sensations and reddening of the skin to blistering and extreme burns. Wild parsnip reactions often appear as long spots or streaks on the skin and are commonly confused with the effects of poison ivy. Unlike poison ivy, you don't need to be sensitized by a prior exposure.
Poison ivy is a wild plant that can cause an itching rash for most people. It grows in thickets in clearings and along the borders of woods, roadsides, in meadows, waste areas, and along fence lines throughout most of Ontario south of a line from North Bay to Kenora.
"Leaflets three – Let it be!" Poison ivy has three leaflets. The stalk of the middle leaflet is longer than the stalks of the two side leaflets. Poison ivy can grow as dwarf, shrubby plants carpeting the ground, as upright plants 60-90 centimetres high or in vine-like form around trees, shrubs and posts. Poison ivy has oil throughout the plant that may sensitize a person’s immune system so subsequent contact with the oil can result in an allergic skin reaction. The reactions may range from mild to severe itchy skin rashes. Tearing or bruising the plant can expose skin to the oil. The oil can also stick to clothing, boots and tools and transfer to other people by touching or rubbing. The oil can be carried by smoke from a fire and if a susceptible person is exposed to the smoke or inhales it, serious allergic respiratory or skin reactions can happen. The oil can also spray from plants when they are cut.
Poison sumac is a wild plant that, like poison ivy can cause an itching rash for most people. It is a native shrub or small tree found in southern Ontario. It’s found in wet woods and edges of swamps and lakes. The sap contains the same sensitizing oil found in poison ivy. Both the foliage in summer and the bare branches in winter can cause a severe rash.
Poison sumac has compound leaves with three to six pairs of leaflets that are nearly opposite each other, plus one terminal leaflet at the tip. Leaflets are pointed at the tip usually with smooth edges and turn red in the fall. Flowers are dull white, produced in hanging clusters. Berries are a whitish or drab colour.
Stinging nettle is a flowering plant with hollow hairs on the leaves and stems, which contain acid and other chemicals. It can be found in large masses in old pastures, flood plains, woodland areas and along stream banks throughout Ontario.
Stinging nettle grows up to one metre tall and its leaves are dark green, egg-shaped, toothed and tapered, measuring five to 15 centimetres long and two to five centimetres wide. Nettles flower from June to September and produce small hanging clusters of greenish-white flowers that are found above where the leaves are attached to the stem.
Stinging nettle can cause a chemical dermatitis or skin inflammation from the acid in hollow hair of the leaves and stems. When touched, the hairs penetrate the skin, breaking off, allowing the acid to enter the skin.
Outdoor plants not to touch
Giant hog weed