| Apr 16, 2009

Back to HomeMaster Gardeners - April 16, 2009 Poison Ivy and other thugs

by Kathleen Lang, Lanark County Master Gardeners

How many times have you broken out in a rash after a day in the garden? And then, have you just assumed that you somehow found some poison ivy?

Good news is that you probably didn’t. But the bad news is that there is a handful of other really common plants everywhere that probably did cause your contact dermatitis (CD).

There are many poisons associated with plants. With the first group of alcohol, alkaloids, carcinogens, hay fever allergens, proteins and amino acids and shellfish poisons (algae), poisoning occurs after ingestion. The second group, glycocides, oxalates, phototoxins, phenols, resins and volatile oils, is the group that is primarily responsible for contact dermatitis (CD). CD can occur with just a casual touch or when plant saps react on your skin when exposed to the UV rays of direct sunlight. Sunscreen will not protect you from these reactions.

Glycocides are toxins in which at least one sugar molecule is linked with oxygen to another compound, often nitrogen-based. They become harmful when the sugar molecule is stripped away, as would happen during digestion or when the compound is exposed to direct sunlight. Common glycocide plants include buttercups (Ranunculus erecta), Nightshade (Solanum nigrum), rhubarb and bracken ferns. The glycocides present in the leaves and sap of these plants can cause skin rashes, itching, redness and/or ulcerations which develop after exposure to the UV rays in direct sunlight.

Oxylates are unstable salts of oxalic acid. When oxalic compounds on your skin are exposed to the ultraviolet rays of the sun, redness, rashes, itching and blisters can occur. Common oxylate plants include rhubarb and skunk cabbage (Lysichiton americanus).

Phototoxins are chemical substances that make the skin sensitive to the UV radiation in sunlight and other light sources. The best plant examples are St. John’s Wort (Hypericum perforatum), Cow Parsley (Anthriscus sylvestris) and Queen Anne’s Lace (Daucus carota). It’s the latex in the sap of the plant, and in the case of St. John’s Wort, in the beads of latex on the leaves, that can be the source of serious skin irritations when activated by direct sunlight.

Phenols are the most notorious plant poison and is the compound found in poison ivy Toxicodendron radicans). Other common phenol plants include poison oak (Toxicodendron diversilobum), poison sumac (Toxicodendron vernix), nettles (Urtica dioica), wild parsnip (Pastinaca sativa), hogweed (aka ragweed) (Ambrosia artemisiifolia), and snow-on-the-mountain (Euphorbia marginata). All parts of these plants, even the pollen, are potentially irritating. Even inhaling the smoke from burning these plants can cause permanent lung damage.

So what can you do to protect yourself? Never weed or use a string trimmer without covering up. Long sleeves, long pants and gloves are a must. Do not touch your face or eyes with dirty fingers. Try converting a long-sleeved cotton shirt into a “gardening shirt”. It is lightweight, and it will protect you from plant compounds and over-exposure to the sun. Before you start weeding or clearing an area, stand back and take a good look for potentially harmful plants before you get up close and elbow deep in them.

As soon as you have finished the job, remove your “gardening clothes” and put them straight into the wash; do not throw them into a hamper where plant saps can contaminate other clothes and linens. Then hit the shower, and wash off any remaining residues from your skin.

If you do develop a rash, blisters or severe itching, seek medical attention immediately.

For more gardening information call Kathlen Lang at 613 283-5982.

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