Poison Ivy, Poison Oak, Poison Sumac or Giant Hogweed (Contact Dermatitis)

Serving Hamilton, Stoney Creek, Grimsby and surrounding areas

Typical Linear Lesions of Poison Ivy Contact Dermatitis

Poison Ivy – Arm

Poison Oak

Poison Sumac

Poison Ivy

Giant Hogweed

Giant Hogweed

Poison Ivy:

  • Poison Ivy is a common plant found in Canada and the United States
  • It can be a vine, shrub, bush, or ground cover
  • In the Niagara Peninsula it can often be seen by the side of the road growing up telephone poles
  • The plant can be recognized by the fact that it has green leaves in groups of three
    • An easy saying to remember is:  “Leaves of three, Let them be!”
  • Some features that may be used to identify poison ivy are:
    • The plant stems are woody and can be found growing in two forms
      • The most frequent form is a trailing vine, with upright leafy stalks 10 to 80 cm high
      • The second kind is an aerial vine that may climb 6 to 10 m high on trees, posts or rough surfaces
    • The poison ivy leaf consists of three pointed leaflets, with the middle leaflet having a much longer stalk than the two side ones
    • The leaflet itself can be extremely variable in shape, from smooth to toothed edges and varies greatly in size, from 8 to 55 mm in length
    • Leaves are reddish when they emerge in the spring, turn green during the summer and become various shades of yellow, orange or red in the autumn
    • The plant produces clusters of cream to yellow-green inconspicuous flowers during the months of June and July
    • Appearing in September, the berries are clustered, waxy and green to yellow in colour
    • The berry ranges in size from 3 to 7 mm in diameter
    • Berries often remain on the low, leafless stems of the plant all winter
  • You can get the rash by touching any part of the plant
  • The only way to get poison ivy is to touch the plant, or to touch something that has touched the plant
  • An example of the latter occurs when you touch the fur of a dog that has been in poison ivy
    • When you touch the plant resin on the animal’s fur, you will develop the rash
  • The rash only appears when you touch the plant a second time
  • The first time that you touch poison ivy, your body becomes sensitive to it, but, there is no rash
  • On the second exposure the rash can be severe with formation of large blisters and intense itching
  • The rash may appear as red swollen areas of skin or rows of blisters forming lines
    • These are areas where the edges of the leaves of the plant have touched the skin
  • You can get the rash at any time of year, even in winter when there are no leaves on the plant
  • The rash does no recur every seven years – this is an old wives’ tale
  • The only way for the rash to return is if you touch the plant again
  • Poison ivy, poison oak, and poison sumac grow almost everywhere in the United States, except Hawaii, Alaska, and some desert areas in the Western U.S.
  • Poison ivy usually grows east of the Rocky Mountains and in Canada
  • Poison oak grows in the Western United States, Canada, Mexico (western poison oak), and in the Southeastern states (eastern poison oak)
  • Poison sumac grows in the Eastern states and southern Canada

Giant Hogweed:

  • Is an invasive weed that was introduced to North America for its ornamental value
  • It has escaped from gardens and is becoming widespread in Ontario, especially by river beds
  • The plant produces a photophotodermatitis – in which contact with the plant, combined with sun exposure may produce a severe blistering rash, similar in appearance to poison ivy contact dermatitis
  • Some characteristics that may be used to identify the plant are:
    • Very tall plants, 3 to 5 metres in height
    • Stems that are 2-4 inches in diameter with rigid hairs, purple blotches and are hollow
    • Leaves that are unevenly lobed and up to 1.5 m wide
    • Flowers clusters up to 2 feet across occurring from mid June to late July
    • Bears a close resemblance to native cow parsley and hogweed
    • Has a reddish purple stem with fine spines that make it appear furry (like a stinging nettle)
    • Has spotted leaf stalks
  • If you must handle this plant be careful not to come into contact with the sap from broken stems
    • You should be well covered, wearing gloves, long sleeves and long pants
  • Giant Hogweed is a short lived perennial weed that reproduces only by seed and is predominantly found along rivers, streams and wet land areas, but can also be found in pasture land
  • If you see giant hogweed, contact the municipality where you live and they should remove it or kill the weed

General Measures:

  • These apply to contact dermatitis from most plants, including poison ivy, poison sumac, poison oak and giant hogweed
  • Do not take hot baths or showers
    • Use only lukewarm or cool water
  • If you have many blisters you can use an oatmeal bath powder in the bathtub
    • This will help the blisters to dry and help with the itching
    • You may break the blisters if they are painful, this will not cause the rash to spread
  • Wash all clothing that may have come into contact with the plant
  • Bathe any pets that may have come into contact with the plant
  • Change seat covers on car seats, or cover the seats, if you think that they may have been contaminated by plant residue on your clothing
  • Be very careful when destroying these plants
    • It is possible to get the rash from the roots, stems, leaves and berries
  • Be especially careful if you burn the plant
    • Inhaling the smoke can cause severe inflammation of the lungs and throat and is very dangerous and can be life-threatening
  • The rash may continue to appear for 2 to 3 weeks after exposure, even if you do not touch the plant again
  • You cannot spread the rash on yourself from the fluid from the blisters
  • The rash is not contagious and you cannot give it to other people


  • A variety of creams and pills are available
  • Please discuss your treatment options with your doctor