Extension Educator, Horticulture
Every time I work in the garden I emerge with some battle scars. The raspberry bush gives me a hug or a rose cane tries to trip me. I usually just consider it my red badge of workage. However one spring I emerged with more than just a few scratches. Soon after working in the garden, I developed blisters on my arm reminiscent of poison ivy. But I knew it had to be something else.
I followed the trail of weed carcasses back through my garden, right past a common ornamental herb called rue. I had heard of people being allergic to rue, but I had never had a reaction. Rue has lovely small, blue-green leaves and grows to 3 feet tall.
Now I understand why I hadn't previously succumbed to rue's dark side. Rue has glands throughout the plant that contain a volatile oil that reacts with the sun (specifically UltraViolet - A) to produce itching, burning, red spots and/or large blisters in some people. The reaction can occur within hours of exposure to the plant and sun. That's the catch - the reaction requires exposure to the sun. The oils in rue are predominantly located on the surface of the leaf so they are easily transferred. In addition, the oils can be transferred to clothing and pets.
Generally the plant's leaves or stems have to be broken to release the oils. This time of year as you are working in the garden also pay particular attention to garden and weed plants in the dill family that can produce the same skin reactions. These include dill, parsley, Queen Anne's lace, wild parsnips, water hemlock, and cow parsnips. Be very careful when mowing ditch banks or weed whacking. I have noticed in yards large numbers of water hemlock plants blooming right now with their ferny leaves and small white flowers.
Some people may get a similar reaction from euphorbias (those succulent plants with white sap), mayweed, gas plant and even lime or lemon juice.
With ornamental plants such as rue and euphorbias you may decide to eliminate these plants from your garden, or you could work around the culprits last to reduce sun exposure. Also wearing long sleeves and gloves in the garden is always a good idea. In addition after gardening, mowing or weed whacking, immediately wash skin with soap and water. Also wash all clothing in hot soapy water and not with the family wash. If you have questions about plants and skin reactions, contact your physician.
Many people are familiar with the rash capabilities of poison ivy; however it is a bit different in that the reaction to the oils doesn't require sunlight. Symptoms usually appear within 24 hours, but may appear in a few hours or a few days.
According to the booklet Pesky Plants by Thor Kommedahl, the reaction of the poison in poison ivy with the skin is nearly instantaneous. However, immediately washing with strong soaps or rubbing alcohol can remove any excess poison that might be transferred to other parts of the body. I like to carry moist towelettes when I'm gardening or hiking just in case I get attacked by another plant.