Last winter, my wife shooed the dog and visiting toddlers away from our poinsettia plants — "they're poisonous, you know." I did not know. But it turns out that the belief that poinsettias are deadly is widespread. The same could be said for mistletoe. What is less clear is if their reputations are deserved.
Could a plant so common and so highly associated with the winter holidays also be so dangerous? If it is dangerous, what problems does it cause? Must it be ingested to cause problems? And if it's not dangerous, why does the myth live on?
The answers to these questions are not easy to find — in fact, you have to go back to 1919, when an army officer's child reportedly died after eating part of a poinsettia plant. In retrospect, it is unclear the plant was responsible because multiple other reports describe mild symptoms (such as nausea or vomiting), but no deaths.
A detailed analysis of almost 23,000 ingestions of poinsettia (published in the American Journal of Emergency Medicine in 1996) found no fatalities, and 96% of the cases required no treatment outside the home and 92% developed no symptoms. According to one estimate, a 50-pound child would have to eat more than 500 leaves to approach a dose that could cause symptoms.
Similarly, pets who ingest poinsettia may suffer gastrointestinal symptoms, but these plants pose no major threat to animals either. Though many people remain convinced of the plant's danger, the idea that poinsettias are deadly seems to be a myth that will not die.
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The story is much the same for mistletoe as it is for poinsettias — it's not particularly dangerous, but may cause an upset stomach if eaten. In fact, mistletoe has been used for centuries as a remedy for arthritis, high blood pressure, infertility and headache.
Recent interest has centered on its potential as an anti-cancer treatment. In fact, many extracts of mistletoe contain chemicals shown to kill cancer cells in the laboratory and to stimulate human immune cells. One of these chemicals, a nitrogen-based substance called alkaloid, is similar to those found in common chemotherapy drugs used to fight leukemia and other forms of cancer. So far, studies of mistletoe offer no proof that it's effective for cancer although it may improve quality of life measures, such as fatigue or depressed mood.
If enough mistletoe is ingested, serious problems or even death may follow, according to some sources. The risk also may depend on the type of mistletoe, as its components vary depending on the type of tree to which it is attached and the time of year it is harvested. However, in a 1984 review published in the Annals of Emergency Medicine, the authors concluded that "ingestion of one to three mistletoe berries or one or two leaves is unlikely to produce serious toxicity." In fact, of more than 300 reports of ingestion summarized, most described no symptoms at all and no deaths.
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How About Holly?
Some have suggested that holly and its berries are dangerous as well. While I could find little information to suggest it is particularly dangerous, eating these plants and their berries may cause crampy abdominal pain, nausea, vomiting and diarrhea. While no one would recommend eating holly, it is unlikely to cause death. And for at least one type of holly, knowing the name would be enough to discourage ingestion — the yaupon holly is also called Ilex vomitoria.
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The Bottom Line
Poinsettias, mistletoe and other holiday plants should not be eaten, but even if small amounts are eaten, they are unlikely to cause serious illness.
Perhaps the most dangerous thing about mistletoe and poinsettias is the choking hazard its berries pose for young kids, but those are not unique to these plants — any toy, food, plant or other small object poses similar risks. If you have any concerns about an ingestion by your child (or pet), contact poison control or your pediatrician (or veterinarian), but unless a large amount is eaten, don't be surprised if the recommendation is simply to "watch and wait."
While it would be unwise to serve poinsettia, mistletoe or holly as appetizers, these plants do not pose significant risks under most circumstances. And it always makes sense to keep on eye on infants and toddlers, to make sure they don't get into anything truly dangerous. As for your pets, most will figure out quickly that these plants are not the best snacks in the house. So, enjoy your holidays — and your holiday plants — and try not to worry too much about their dangers.
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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.