If the sap of the wild parsnip plant comes in contact with human skin and is not washed off, it can cause phytophotodermatitis, which makes the skin extremely sensitive to sunlight, leading to rashes and blisters. Experts recommend washing the affected area as soon as possible and staying out of sunlight or covering exposed skin to prevent a burning reaction. Cortisone medication may help reduce symptoms.
The best way to avoid a nasty run-in with the toxic weed is to keep skin covered and wear gloves when gardening.
Wild parsnip can be found throughout most of the U.S., with the exception of Hawaii, Mississippi, Alabama, Georgia and Florida.