Topic for Mar. 13. ( Thur )

[Alex !]

Study reveals men prefer innermost restroom stalls while women choose entrance

Recent studies have shown that pathogens can spread when flushing the toilet, leading many people to hesitate to use restrooms in unfamiliar places. However, if it is difficult to hold back natural urges, the best option is to look for stalls that are used less frequently by others. Which stalls do people prefer to choose in restrooms? Is there a difference in restroom selection criteria between men and women? Psychologists suggest that knowing which side people prefer under the same conditions can help find relatively cleaner restrooms.

◇Avoid stalls that are frequently used by many people

The first strategy discussed by psychologists is to avoid the middle stall in restrooms. Humans unconsciously prefer the center. Since people tend to choose the center stall in the restroom as well, the hygienic conditions are likely to be worse than in other stalls.

Nicholas Christenfeld, a professor in the psychology department at the University of California, San Diego (UCSD), published in the international journal Psychological Science in 1995 that there is a 'center bias' where people prefer the middle if the conditions are the same.

For instance, if there are four rows of the same product on a supermarket shelf, 71% of shoppers purchased items from the middle two rows. Only 29% bought items from the front and back rows. Surveys also showed a tendency to indicate the middle two stalls among four. The same applies to restrooms.

Researchers investigated which of the four stalls in a public restroom at a California beach had the most toilet paper replaced over a span of 10 weeks. The analysis found that 60% of toilet paper was used in the two middle stalls during this period. If people had chosen randomly, the use of toilet paper in the middle two stalls should have been almost equal to that of the edge stalls. It can be said that one should opt for the edge stalls, which are less frequented, to encounter fewer pathogens.

◇Men prefer the innermost stall, women prefer the one near the door

The strategy of avoiding the middle stall is effective for both men and women. However, where to go among the remaining stalls is somewhat different. In 2015, New York Magazine surveyed the stalls preferred by men and women in restrooms. Both genders preferred the middle stall, but their subsequent choices differed. Men chose the closest stall to the door as a backup if the middle stall was occupied. Women sought either the middle or the stall farthest from the entrance.

Combining center bias and the fallback options for men and women, we can conclude that since the middle and door-adjacent stalls in men's restrooms are used more often, the innermost stall is relatively cleaner. Conversely, in women's restrooms, the middle and innermost stalls tend to be crowded, making a stall closer to the entrance more hygienic.

The earlier research was conducted in restrooms where both edges are adjacent to walls. What if one edge has shared space on the side? In 2023, Thomas Heston, a professor at Washington State University's medical department, reported that in this type of three-stall restroom, the edge with one side against a wall and the other side adjacent to another stall had a utilization rate of 62%, the highest among stalls.

The middle stall and the stall exposed to shared space had utilization rates of 30% and 32%, respectively. Professor Heston noted, "People tend to perceive that stalls with one side against a wall and the other side adjacent to another stall are the most private and safe." This suggests that if one seeks to find less frequently used stalls for hygiene, it might be better to sacrifice some privacy.

◇Restroom studies during COVID-19

The fact that restrooms can be a space for spreading pathogens was confirmed in successive studies during the COVID-19 pandemic. In June 2020, a research team from Dongnan University in China announced in the journal Physics of Fluids that flushing a toilet generates aerosols containing viruses. In August of that year, researchers from Yangzhou University in China revealed in the same journal that using a urinal can also generate aerosol clouds.

A research team from the University of Colorado published a paper in 2022 in Scientific Reports demonstrating visually that flushing a toilet generates aerosols by firing a laser. The aerosols were ejected above the toilet at a speed of 2 m per second and reached a height of 1.5 m within 8 seconds. Scientists raised concerns that if a person infected with COVID uses the restroom, virus particles could spread through aerosols.

Last month, Chinese researchers revealed that flushing a toilet after defecation releases Escherichia coli and Staphylococcus aureus into the air above the acceptable limits set by the U.S. Centers for Disease Control and Prevention (CDC). The researchers noted that activating an exhaust fan may reduce the risk of bacterial aerosol release by one-tenth.

Of course, it is essential to close the lid before flushing the toilet. According to Chinese researchers, toilets without lids emitted 42% to 62% more Staphylococcus aureus than bidet toilets. Closing the lid before flushing makes it possible to see that effect. Additionally, properly washing hands before and after using the restroom is crucial. If everyone uses the restroom cleanly, the effort of finding empty stalls by considering various options may be reduced.