Touch one on a sunny day, and you're likely to have a nasty blister, similar to poison ivy. But it is the sap that causes the real damage. The plant exudes a clear watery sap which sensitizes the skin to ultraviolet radiation. This can result in severe burns to the affected areas resulting in severe blistering and painful dermatitis. These blisters can develop into purplish or blackened scars. It does this through chemicals called furanocoumarins, which react with DNA in skin cells, cross linking the strands and making them permanently susceptible to damage by sunlight. Contact with the eyes may cause blindness. The dried seeds are apparently used in Iranian food, but the rest of the plant is poisonous to ingest.
Thanks to Bud Clark for this information.