With all due respect to Paracelsus, this is an oversimplification and
irrelevant here.

Poinsettia is a member of the Euphorbiaceae, most of which are
dangerously toxic; thus it is supposed among some that Poinsettia is
also toxic. But the toxic principles found in other Euphorbias are
distinctly absent from Poinsettia, and there is no evidence that
Poinsettia sap is anything worse than a mild, if annoying, irritant at
any exposure. There is only one published case of death attributed to
Poinsettia poisoning, and it is unsubstantiated.

--
Chris Green