Naturally Speaking

The poisonous aspects of wild parsnip can be explained in a single word: phytophotodermatitis.
Latin words used as science terms are a shortcut to writing many sentences to say the same. But one has to know a bit of Latin, or the term becomes nonsense.
There are three parts to phyto-photo-dermatitis.  Phyto means plant; wild parsnip in this instance.  Photo means light; sunlight here.  And dermatitis refers to the skin becoming inflamed or blistered when the plant juices and sunlight come together.
When the plant's juices get on someone's skin, the skin becomes more sensitive, or hypersensitive to ultraviolet light.  That's more Latin.  Hyper means higher or more, as opposed to hypo, which means lower, less or under.  A hypodermic needle goes below the skin.
Occasionally phytophotodermatitis is called lime disease.  No, not Lyme disease as in the bacterium deer ticks transfer, and named for Lyme, Connecticut, where Lyme disease was identified.
The reference to lime disease is in the juices of a lime fruit. (Notice the other disease is Lyme disease, not Lyme's because the city in Connecticut is named Lyme, not Lymes.)
The lime juice will do the same thing as the juices from the wild parsnip, but the reaction is less severe. This led some doctors to refer to wild parsnip phytophotodermatitis as margarita dermatitis, too, because of the lime juice is used to make the drink.  Don't spill juice on yourself while having a margarita on a patio.