Timber, not concrete, stainless steel, or plastic, could hold the key to safer and more hygienic hospitals. That is according to research from the University of Oregon, revealing that exposed wood has lower levels of bacterial abundance (and could therefore resist microbial growth when briefly wet) compared to plastics.
“People generally think of wood as unhygienic in a medical setting,” said assistant professor Mark Fretz, co-director of the UO’s Institute for Health in the Built Environment and principal investigator for the study. “But wood actually transfers microbes at a lower rate than other less porous materials such as stainless steel.”
Fretz is part of a team of UO researchers, which also includes scientists at the Salk Institute of Biological Studies and Portland State University, exploring what happens when wood gets wet and then dries. The most recent study, “Effects of Wetting Events on Mass Timber Surface Microbial Communities and VOC Emissions: Implications for Building Operation and Occupant Well-being,” demonstrates the impact of moisture on surface microbes and volatile organic compound emissions from mass timber.
While mass timber has emerged as a popular alternative to steel-and-concrete construction systems, especially in multi-residential construction, wood is rarely used in healthcare facilities, despite emerging research showing the value of engineered wood products in medical settings. That’s due in part to strict building codes that are slow to evolve, Fretz said. Another reason is the widespread misperception about wood and pathogens:
“We wanted to explore how mass timber would stand up to the everyday rigours of health care settings,” said Gwynne Mhuireach, a UO research assistant professor. “In hospitals and clinics, germs are always present, and surfaces occasionally get wet.”
Cross-laminated timber transfers microbes at a lower rate than steel.
For the latest experiment, blocks of cross-laminated timber were sealed in disinfected plastic boxes to create a micro-environment with carefully controlled temperature and humidity. To simulate a healthcare setting, air was filtered and exchanged at rates similar to hospital codes.
The team then sprayed the blocks with tap water, inoculated them with a cocktail of microbes commonly found in hospitals, and took samples over a four-month period. An empty plastic box was used as a control. The researchers then compared coated and uncoated wood samples under three types of water spray events: once, daily over a four-week period.
The results of the study indicated wood is effective at inhibiting bacteria and revealed clues about wetting that will inform future research and development, Mhuireach said. The empty plastic control box had greater viable microbial abundance than the wood samples, excluding the first 14 days after inoculation.
Wetting the wood blocks reduced the abundance of viable bacterial cells, with no discernible difference between coated and uncoated specimens. During wetting, the microbial composition reflected what is common in tap water more than the hospital pathogens the team introduced.
The experiments were the first to explore relationships between microbial communities on cross-laminated timber surfaces and the emission of volatile organic compounds, or VOCs, under dry and wetted conditions, Mhuireach said. VOCs are chemicals that spread quickly in the air and are responsible for odours as diverse as perfume, mould or “new car smell.” Some present health hazards, but others are beneficial.
Wood can emit compounds called terpenes. Many smell pleasant and inhibit microbial growth. Mhuireach added that there was a plateau in VOC emissions after wetting, which the team interpreted as a slight increase compared to an overall downward trend.
The study marks another milestone in the UO’s work to promote the use of mass timber in healthcare facilities. That effort began in 2020 with funding from a Wood Innovations grant from the U.S. Department of Agriculture, which was crucial in helping to fund the study, Fretz said. That led to the formation of a focus group comprising architects, engineers, and experts in healthcare building codes.
Healthcare is a growing market for mass timber construction.
Through his work with the TallWood Design Institute, a collaboration of the UO and Oregon State University, Fretz has been working to promote the production and use of mass timber, including materials manufactured in Oregon. Mass timber construction, which began in Europe, is growing fast in the United States, with Wood Central last year reporting that the North American market is now among the world’s fastest-growing markets for cross-laminated timber.
“Stronger per pound than steel or concrete, mass timber boasts a smaller carbon footprint. Exposed wood also promotes Health and healing,” Fretz said, “because it appeals to our inherent tendencies to connect with nature.” Wood Central understands that the benefits of this human trait, which architects and designers call biophilia, extend beyond mere aesthetics, with numerous studies linking biophilic design to improved healthcare outcomes, including shorter hospital stays, faster healing, and enhanced mental well-being.
Wood’s ability to inhibit the spread of pathogens may stem from pores that trap bacteria or antimicrobial chemical compounds that occur naturally, Fretz said. It could also result from wood’s capacity to absorb moisture. A respiratory virus shed indoors travels in a droplet of water. Wood will dry out that droplet faster than plastic or stainless steel, thereby reducing the time virus survival.
Citation: Mhuireach GÁ, Collins S, Dietz L, Horve PF, Laguerre A, Northcutt D, Stenson J, Wymelenberg KVD, Gall E and Fretz M (2025) Effects of wetting events on mass timber surface microbial communities and VOC emissions: implications for building operation and occupant well-being. Front. Microbiomes 4:1395519. doi: 10.3389/frmbi.2025.1395519
