Unlike poison ivy, you don't need to be sensitized by a prior exposure. Wild parsnip causes a non-allergic dermatitis that can occur with the right combination of plant juice and sunlight. Parsnip is only dangerous when the juice gets on skin from broken leaves or stems. Generally, wild parsnip causes a modest burning pain for a day or two, and then the worst is over. The itch and discomfort from poison ivy, in contrast, can drive people crazy for a long time.
Some unanswered questions remain.
I did not test, nor did I find in the medical literature, how long skin remains sensitive to sunlight after being exposed to parsnip juice. I invite all interested readers to consider the two questions listed below. Send your responses to the e-mail address following the questions, and together we can add to what's already known about these fascinating species. Tell the tale. An update on wild parsnip and other phototoxic plants, which will include your feedback, will appear in a future issue of Wisconsin Natural Resources magazine.