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Christmas trees

A word to the wise before the holidays: Mold grows fast on Christmas trees. “When you put that tree in a bucket of water, invisible mold grows almost immediately,” Dr. Wedner says. “Most people are allergic to or irritated by mold spores.”

What to do: Try a fake tree. Can’t live without a real one? Ask when it was cut down before you buy it; trees that were cut weeks in advance are already ripe with mold. Then, starve it of water and keep it for as short a period as possible. Mold grows on houseplants, too, so keep them on the dry side.