Poinsettias are NOT toxic.
NO, I repeat, NO deaths have ever been reported due to a person eating a poinsettia.
The rumor that poinsettias are poisonous stems from a single report of the death of a child in Hawaii in the early twentieth century that was mistakenly attributed to the child’s consumption of a poinsettia leaf.
A benchmark study conducted by Ohio State University, with the cooperation of the Society of American Florists, indicated that the American poinsettia presented no toxicity at levels far higher than those likely to occur in a household incident. Every part of the plant was tested, and the experimental exposure was roughly equivalent to a 25-lb. child eating over 250 poinsettia bracts (the colored leaf the plant is prized for). POISINDEX Information Service, a resource used by most US poison control centers, states that a 50-lb. child would need to eat in excess of 600 leaves to exceed the experimental doses.
Poinsettias are an ornamental plant and not intended for consumption. If they are eaten the most likely effect is digestive tract and intestinal irritation, potentially up to and including vomiting and diarrhea.
The leaves have a reportedly bitter taste. This makes it extremely unlikely that a person would consume enough of the plant to make them ill. This is less of a deterrent to animals, so if you have a pet that likes to chew houseplants you may want to avoid decorating for holidays with poinsettias.
European poinsettias have been shown to have a slightly higher toxicity level than the American varieties, but are still considered generally safe to have in the home.
They ARE a documented skin irritant.
Poinsettias have a latex sap, similar to that of poison ivy or poison oak but considerably milder, that can cause itching, irritation, and blistering on contact with skin. Most sites I found recommend immediate washing with a mild soap and water. A person or pet ingesting a poinsettia would also suffer mouth irritation due to the sap.
If someone in your family has a particularly severe reaction to poison ivy or poison oak you may want to avoid having live poinsettias in the house, just to be on the safe side.