When I realized this column would run on Valentine’s Day, I started churning themed ideas about a great number of topics. Plants I love, plants I love to hate, and my infatuation with winter-blooming shrubs. Instead, I settled on the topic of plants I love, but don’t always love me back.

Rather than returning love, there are certain plants that requite itchy skin, mild rashes and puffy eyes — more commonly known as contact dermatitis. After almost 20 years of working with plants, I’ve learned that I can’t handle juniper, arborvitae, dogwood foliage, or hyacinth bulbs without expecting a mild rash on exposed skin.

When it comes to why certain plants irritate our skin, the cause is usually due to a chemical irritant, a mechanical irritant, or a photo-toxic reaction. There are a fair number of plants that are dangerous to handle, such as poison ivy (which have a chemical irritant) or vines covered in jagged thorns (mechanical irritant). But other plants aren’t as obvious with their malevolent capabilities.

Anything in the thuja (arborvitae) plant family has an adverse effect on my skin. Even though the most common cultivars of this conifer have soft, fan-like branches, repeated exposure can result in contact dermatitis. Junipers are notorious for causing contact dermatitis. They have small needle-like foliage, which can quickly irritate skin. When I prune or handle junipers, my skin breaks out in red blotches, followed by raised bumps.

My reaction to arborvitae and juniper may be due to a chemical component in the foliage itself, but I had little luck finding the specifics of the chemical makeup of these plants. One thing is certain, though — plants are smart, and most have evolved or adapted to ultimately survive.

“I do know that plants have adaptations for protection,” said Lisa Swarthout, a horticulture professor at Forsyth Tech Community College. “Stinging nettle, for example, has hairs that break off when touched and inject a chemical in the skin. People and animals avoid plants like these.

“Many plants have other adaptations for protection, like protective structures, thorns, spines, prickles and epidermal hair. Plants have evolved in very specific ways to protect themselves and ensure their species live on — including chemicals in the hairs that irritate.”

There are tons of plants that have chemical irritants. The stems and foliage of native asters and black-eyed Susans can trigger contact dermatitis. Many chemical irritants are based in the sap of plants. Poinsettias and euphorbias have latex-based sap which can irritate skin. The sap of anemone and hellebore contains protoanemonin — a chemical that can cause a rash and blisters if exposed to skin.

Hyacinth bulbs contain calcium oxalate crystals, which are sharp and can irritate skin and eyes. I’ve had very strong reactions to hyacinth bulbs in the past, so if I handle them, I make sure to wear gloves and wash up immediately afterward.

Mechanical irritants are sometimes obvious, but not always. Thorns on a smilax or prickles on a rose are clear indicators to stay away. The stinging nettle that Swarthout mentioned is a perfect example of an inconspicuous irritant. The stinging hairs on this plant are quite often overlooked until the damage is done.

Certain plants can cause photo-toxic reactions that result in blisters, swelling, rashes and hives. These photo-toxic reactions occur when plant sap is exposed to sunlight and then transferred to our skin. Parsnip, Queen Anne’s Lace, wild parsley, citrus, celery, and members of the carrot family can all cause phytophotodermatitis, which gives you a blistery rash.

According to Healthline.com, “phytophotodermatitis is caused by exposure to furocoumarins, a type of chemical found on plant surfaces.” The chemical is activated by sunlight, and if your skin comes into contact with the plant during that time, then you are susceptible. It’s important to be cognizant of these plants and this reaction, because we usually work in our gardens when the sun is shining.

Over time, I’ve learned that the majority of gardeners deal with this same love-hate relationship of plants and skin irritation. We can usually avoid it by wearing long sleeves, long pants and gloves. So if you know you’ll be exposing yourself to harmful plants, take precaution. An ounce of prevention is worth a pound of cure.

If you have a gardening question or story idea, you can find Amy Dixon on Facebook at www.facebook.com/WSJAmyDixon. You can also send an email to her attention to news@wsjournal.com. Put gardening in the subject line. Or write to Amy Dixon in care of Features, Winston-Salem Journal, 418 N. Marshall St., Winston-Salem, NC 27101

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