The white stuff that comes out of poinsettia plants is the plants sap.
The poinsettia plant naturally and regularly excretes the white stuff or sap and it's regularly excreted onto the leaves of the poinsettia.
The white stuff coming out of the poinsettia plant is a milk liquid that is referred to as latex since the poinsettia plant is a member of the Euphorbiaceae family, which also includes the rubber tree.
Latex is associated with rubber so that's why it's referred to as latex.
There's nothing wrong with your poinsettia plant when it has white stuff coming out of it and it's perfectly natural to see that.