From Our 2007 Archives

Christmas Trees: Source of Indoor Mold?

Study Shows Trees May Bring Allergy Symptoms Along With Holiday Cheer

By Patricia Kirk
WebMD Health News

Reviewed By Louise Chang, MD

Nov. 12, 2007 -- Live Christmas trees may bring more than the fresh pine scent of the holiday season into homes, according to a new study.

The study, which was presented at The American College of Allergy, Asthma & Immunology Annual Scientific Meeting in Dallas, examined the relationship between mold growth on live Christmas trees and poor indoor air quality.

This study grew out of a consistent and dramatic increase in asthma and sinus complaints among patients every winter, which is especially pronounced during the holiday season, notes study researcher John Santilli, MD.

"As mold growth is common in the area surrounding outdoor foliage, we hypothesized that the presence of a live Christmas tree may be contributing to indoor mold," he says.

Indoor Mold Levels Rise

Twelve times during a two week period, researchers measured mold counts in a roomcontaining alive Christmas tree, beginning when the tree was brought inside and decorated. The tree was located 10 feet from a heat vent, and the indoor temperature was maintained at between 65 and 68 degrees.

For the first three days, counts remained at 800 spores per cubic meter of air, then began escalating, rising to a maximum of 5,000 spores per cubic meter by day 14, when the tree was taken down.

Mold allergy affects up to 15% of the population, according to Santilli, and people with sensitivity to certain molds commonly experience nasal, eye, and throat irritation; nasal stuffiness; and headache. Additionally, there is a well-documented link between asthma attacks and molds, and the added risk of invasive fungal disease among people with compromised immune systems.

Santilli says normal indoor air has a mold level of 500-700 spores per cubic meter; anything higher indicates a source of mold growth inside the building.

"Ventilation systems and water-damaged areas have long been recognized as sources of mold, but we need to continue to search for new and unique sources of contamination," Santilli says.

Avoiding Indoor Mold

"Our study demonstrates that a live Christmas tree can be a significant source of mold spores. Therefore, we recommend families with allergies in general and mold allergies in particular not keep a live Christmas tree in their homes for more than a few days at most, and remove it sooner if there are signs of increased allergy symptoms," Santilli says.

Rebecca Gruchalla, MD, PhD, chief of allergy at the University of Texas Southwestern Medical School in Dallas, says the relationship between live Christmas trees and a rise in indoor mold spores comes as no surprise, particularly since most Christmas trees are cut well in advance of the holidays and stored in a moist environment before being placed on a lot for sale. Then they're then taken home and placed in water too, she says.

Gruchalla notes that artificial trees and ornaments collect dust in storage and, therefore, are another source of allergy irritation.

She suggests taking both live and artificial trees outside and shaking them out before bringing them inside to decorate.