Wild parsnip is a summertime weed rather common in southeastern Minnesota.
A recent article in social media discussed noxious weed species invading the region. While a good article, it said, “Wild parsnip contains toxic chemicals that cause serious blisters and burns to skin.”
The extreme end of the reaction spectrum can feel that way, but most reactions are just obnoxious and cranky, and some not even noticed until the second reaction of hyperpigmentation appears.
These are designated medically as phytophotodermatitis (fito-foto-dermatitis) — translated plant (phyto) and light (photo) dermatitis.
Now comes the science: Ultraviolet light energy comes in wavelengths shorter than visible light. The longer portion of that spectrum is dubbed UVA, shorter being UVB, and even shorter UVC.
The chemicals referred to are called psoralens (SOR-a-lens), which are “all-natural,” and occur in as many as 14 families of plants, depending on what reference you read.
The family of wild parsnip is Umbelliferae, because the bloom takes an umbrella-like shape. Many common vegetables contain psoralens also, like carrot tops, dill, lime peelings used often in alcoholic drinks, the decorative plant Rhus (not related to poison ivy) and Queen Anne’s lace.
The parsnip psoralens are external on the plant. Other plants might have to be crushed to expose the chemicals.
Psoralens by themselves produce no reaction. They are, however, excited by UVA to create two totally separate skin reactions. The first is inflammation. It is completely dose dependent, meaning the degree of redness and blistering, if any, depends on how much psoralen reaches skin, and how much light exposure it gets.
A little of both only makes a mild reaction. A large exposure can bring out big juicy blisters that do temporarily burn, hurt, and itch. It is most often confused with poison ivy rash and generally comes out about 48 hours after exposure.
The level of blistering is in the mid-epidermis, the top portion of skin. Sunburn and poison ivy blisters are lower down. The parsnip and ivy reactions never scar. Often, there is just a remnant of red as a sign of contact, with no sensation, which fades in a few days. Nothing is contagious.
The second totally independent reaction that follows the redness is stimulation of your pigment cells to make much more melanin or brown pigment than usual.
The color can last for months, and it is not possible to lighten or remove. This was known as long ago as 1300 B.C. in Egypt. The plant along the Nile, called Ammus maji, was distilled into an internally consumed liquid, and people with pigment loss purposely and carefully exposed themselves to sun to try to re-color areas of what is vitiligo, a skin disease that causes loss of pigment.
Some leprosy types cause pigment loss, and nobody wanted to be thought a leper, so it was very important to have uniformly colored skin. In our day, the psoralens were put into pills explicitly for tanning, but are rarely used anymore with the solar paranoia.
The only truly medical seriousness of phytophotodermatitis is how miserable it makes the person, or how confusing it could be to figure it out from other dermal derangements.
One summer a mom brought in a toddler with a brown, oddly streaky, no-symptom rash on one leg. Mom had a couple spots on her torso. Dad had a bunch here and there, and one brother did, too.
They noticed them at the end of a trip the week before, and naturally wondered whether something on the trip was the culprit. Wait! They had been chopping down weeds big-time back of their yard just before leaving. Aha! Quite likely some parsnip nailed them, caused no redness, but the later color.
Hopefully this puts wild parsnip into perspective a bit. It is an invasive, a biennial/perennial herb native to Eurasia.
But, perhaps somehow, we can learn to co-exist.
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