The question
Should you keep your shower curtain open or closed to help prevent mold?
The science
After a bath or shower, you probably don’t think much about the shower curtain. You may wipe the condensation from the mirror, brush your teeth and dart out the door. But the decision to leave the curtain open or closed may matter as part of a larger effort to dry out your bathroom and prevent mold growth.
Our homes have a rich microbiome consisting of bacteria, viruses and fungi that can come from the outdoor air, our shoes and pets — and most of them don’t pose a serious threat to us, said Karen Dannemiller, an associate professor of civil, environmental and geodetic engineering at the University of Ohio, where she directs the indoor environmental quality research group.
“Where you get into trouble is when you start to have fungal growth, or mold, that you start seeing or smelling in your home,” she said.
When bathroom moisture poses a problem
Mold can cause various health issues, including allergy symptoms such as a stuffy or runny nose, sneezing or itchy eyes; attacks in those with asthma; or an immune-mediated lung condition that can cause coughing, shortness of breath and fatigue, among other symptoms, in people with immune system issues or preexisting lung problems.
Indoor mold growth indicates that there is a problem with moisture or water and should be addressed immediately, according to the Centers for Disease Control and Prevention.
Relative humidity — the amount of water vapor in the air compared with the amount it can hold — should be between 30 and 50 percent for our comfort and overall health, according to the Environmental Protection Agency. Too far above that, and mold can begin to grow.
This is especially a concern in bathrooms where water and humid air, under certain circumstances, can linger. Moisture on some bathroom surfaces can, for hours, stay at a level that may lead to mold growth, Dannemiller said.
How to prevent mold in the bathroom
Here are some general guidelines to prevent mold:
- Reduce the amount of water on bathroom surfaces after a bath or shower, said William Nazaroff, a professor emeritus of civil and environmental engineering the University of California at Berkeley. Use a squeegee to get water off the shower walls and into the drain or a washcloth to dry off the shower surfaces, he suggested. Removing water from surfaces means it doesn’t have to be eliminated through evaporation and ventilation, which is the only other way, he said.
- Control moisture in the air through adequate ventilation. Open a window or turn on an exhaust fan that vents outside and leave it running during and after showering until the condensation on the bathroom mirror clears. This will help remove water that is in the vapor phase, Nazaroff said.
- Stretch the curtain to allow it to dry out but leave about six inches of space on either side so air can flow between the shower and the rest of the bathroom, Nazaroff said. If you have a shower door, leave it cracked, he said. If you scrunch up the curtain after a shower, “it will stay wet long enough to create a risk of mold even if everything else has dried off nicely,” he said.
“What we’re trying to do is reduce that timescale for the bathroom to completely dry from many hours to an hour or so,” Nazaroff said.
What else you should know
There are other things you can do to reduce moisture and remove mold.
- Leave the bathroom door open after a bath or shower to increase airflow and speed up the drying process. Humid air from the bathroom is unlikely to pose a humidity problem to the rest of your home because the air outside the bathroom is usually dry enough to accommodate it — unless humidity levels are already high or the bathroom opens into a small, contained space such as a basement, said Mikhail Sogonov, an indoor mold inspector. In rare cases, bathroom humidity may pose a threat to other parts of your home if, for instance, your bathroom exhaust fan was installed incorrectly, venting into the attic instead of outside, Sogonov said. “That can create humidity — and eventually mold — problems in the attic,” he said.
- If humidity is a concern, you can buy a humidity meter, also known as a hygrometer, which is a relatively inexpensive way (you can often buy one for less than $10) to monitor the levels in different rooms. And if you consistently see readings above the recommended threshold of 50 percent, consider a dehumidifier, which pulls in the moist air, passes it over cold condenser coils to remove moisture and blows out drier, warmer air into the room.
- If you find visible mold in your home, you can clean it up yourself if the area is less than 10 square feet, such as a 3-foot by 3-foot patch of wall, but abide by the EPA’s remediation standards such as wearing a respirator, gloves and goggles to protect yourself from exposure; scrubbing off mold on hard surfaces; and potentially throwing away porous materials. If the area is larger than that or if there are health concerns, call a professional mold remediator, experts said.
The bottom line
Leaving the shower curtain or shower door cracked after a bath or shower increases airflow and speeds up drying time. Also, reducing surface water and ensuring there is adequate ventilation helps minimize and remove moisture from the air in the bathroom.
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