Michelle Grant of the Tennessee Poison Center in Nashville cautions that mistletoe should be kept away from children and pets -- especially the berries. Mistletoe berries, and to a lesser extent the leaves and stems, contain poisonous substances that slow the heart, she says. In fact, swallowing just a few mistletoe berries can cause serious problems for a toddler.
Holly berries can contain ilex acid, which can causes nausea, vomiting and diarrhea. A child usually must swallow several holly berries before serious problems develop, Grant says.
One of the more toxic plants displayed at Christmas is the Jerusalem cherry plant. Its bright yellow-to-red berries contain solanine, which, when ingested, causes vomiting and diarrhea, slows the heart, lowers blood pressure, depresses breathing and induces coma.
"However, poinsettias are not toxic and do not pose a health threat," she explains. "But like many houseplants, poinsettia leaves and stems can cause a minor upset stomach -- nausea, vomiting and diarrhea -- if swallowed by young children or pets."
In addition, any plant can present a choking hazard, Grant says.