In 2011, NSF International conducted a "Germiest Places in the Home" study to identify germ hot spots in the home. NSF's microbiologists asked 22 families to swab 30 everyday household items ranging from kitchen surfaces to cell phones to pet items in order to measure contamination levels of yeast, mold and coliform bacteria (a family of bacteria that includes Salmonella and E. coli).

Before testing these items, the volunteers were asked to rate the items they thought would be the dirtiest. The findings from this study indicated that there are common misconceptions about where the highest concentration of germs is found in the home.

The biggest misconception identified through the study was that people thought the bathroom is the dirtiest place in the house when in fact the kitchen had the most germs. NSF swabbed for coliform bacteria - a family of bacteria that includes Salmonella and E. coli and is an indicator of potential fecal contamination – and found coliform on:

• More than 75 percent of dish sponges/rags
• 45 percent of kitchen sinks
• 32 percent of counter tops
• 18 percent of cutting boards

This compares to the bathroom where areas with the most coliforms only included:

• 27 percent of toothbrush holders
• 9 percent of bathroom faucet handles

According to the study’s findings, the areas in which food is prepared actually contained more bacteria and fecal contamination than many other places in the home.

Best Breeding Environment for Germs

Warm and moist environments tend to be a breeding ground for germs. NSF’s analysis revealed that sponges and coffee reservoirs, which may not be cleaned as frequently as they should be, were in the top 10 germiest places in the home. In contrast, smooth, cold surfaces tend to harbor fewer germs. For example, NSF’s analysis showed that keys, money, computer keyboards and game controllers did not tend to harbor many germs.

Read the full executive summary and findings from NSF’s 2011 Germ Study