Machineel trees, found along many beaches in the Caribbean, bear a poisonous fruit similar to a crabapple. Not eating the fruit is easy enough, but they also have irritant sap that blisters the skin, similar to poison ivy and poison oak. Even standing under these trees during a rainstorm can bring on a major festering nightmare. On major tourist beaches, the machineel trees generally have warning signs.
I did not heed these when in St John and my bushwhacking earned me a knee and elbow of itching ecstasy. Steroid lotions, detergents, Claritin, and voodoo have calmed it down to tolerable in just two weeks.