Confirmation that dust from toilet paper serves as a nutrient source for 'odor-causing bacteria' in toilets

Lion Corporation (President and Representative Director: Masayuki Takemori) has confirmed that Micrococcus luteus (M. luteus) and Kocuria marina (K. marina), which are the causes of toilet odors, use not only urine stains but also dust generated when using toilet paper (paper dust) as a nutrient source to multiply. Furthermore, while these two types of bacteria cannot survive for even one day in conditions without urine or paper dust, they were found to grow for two weeks to one month when such dirt is present. This research was presented at the 2025 Indoor Environment Society Academic Conference (held at the Kitakyushu International Conference Center, Fukuoka Prefecture, from December 2 to December 5, 2025) and received the Chairperson's Encouragement Award (Technical Division). Regarding the research background, consumers often feel dissatisfied with lingering odors despite frequent cleaning. Previously, the company identified that these odor-causing bacteria exist not only around the toilet bowl but throughout the entire bathroom space, including floors, walls, and ventilation fans. This study investigated the impact of urine stains and paper dust on the growth of these bacteria. The results showed that in the presence of urine or paper dust, both types of bacteria increased in number and their survival period was significantly extended. Additionally, it was confirmed that paper dust rises with the airflow from ventilation fans and spreads throughout the entire bathroom space. In conclusion, to suppress odors, it is essential to eliminate urine and dust, including in hard-to-reach areas, to prevent the growth of odor-causing bacteria. Lion's Living Care Meister advises that future toilet cleaning should focus on the entire space, including ventilation fans and ceilings, in addition to the toilet bowl and floor.