The Science Behind the Sponge

Having seen the scary headlines about sponges being “dirtier than the toilet seat” and that “disinfecting makes germs stronger,” Skura Style founders Linda Sawyer and Alison Matz wanted to learn what makes this basic kitchen tool so gross. They spoke to noted researcher Dr. Charles P. Gerba, known as “Dr. Germ,” to get answers to the questions they were almost afraid to ask. Dr. Gerba is a professor of microbiology and environmental sciences at the University of Arizona, and his award-winning research is often covered in the news.

Is the kitchen sponge really germier than the toilet seat?

In short, yes. While there are bacteria in both bathroom and kitchen, the most contaminated sites are those that stay moist and are touched frequently, like things around the kitchen sink. That’s why more bacteria were found on sponges and dishcloths than toilet seats.

In the kitchen, what’s the biggest offender for spreading germs?

Cleaning tools such as sponges and cloths are known to harbor large numbers of bacteria and are a potential source of spreading microorganisms throughout food-prep areas during use.

What types of germs did you study in your research?

Bacteria such as coliforms like Escherichia coli (E. coli) and non-coliforms like Salmonella.

If a sponge doesn’t stink, is it safe to assume it’s germ-free?

No! Salmonella and E. coli do not have an odor, so just because your sponge is odorless it doesn’t mean it’s free of all bacteria.

Are all sponges created equal? What differences did your research uncover?

In our study, polyurethane sponges always had fewer total bacteria than cellulose sponges. Cellulose, however, dominates in the American market despite the clear benefit of polyurethane.

How often do you recommend that people replace their sponges?

Germs really start to multiply in about seven to eight days, so either a thorough sanitization or replacement after one week is recommended.

Antimicrobial protection on the sponge inhibits the growth of odor-causing bacteria, mold and mildew. It does not disinfect surfaces.

Sources: Conversation with Dr. Charles P. Gerba, September 1, 2017; “A Comparison of Urethane and Cellulose Sponges as Cleaning Tools in Household Kitchens,” Charles P. Gerba, Laura Y. Sifuentes and Akrum H. Tamimi, Food Protection Trends, May/June 2017; “Reduction of faecal coliform, coliform and heterotrophic plate count bacteria in the household kitchen and bathroom by disinfection with hypochlorite cleaners,” P. Rusin, P. Orosz-Coughlin and C. Gerba, Journal of Applied Microbiology, June 1998.