Several studies have confirmed that the bottoms of our shoes commonly carry any number of potentially harmful strains of bacteria. A study published in a 2014 issue of Science Direct noted that shoe bottoms were the highest carrier of Clostridium difficile (C. diff) in all of the common household items or environmental dust tested -- 39.7 percent of the shoes tested were positive for the bacteria, which can cause life-threatening intestinal infections. A University of Arizona study found "large numbers" of bacteria on the bottom and inside of shoes, including: Escherichia coli (E. coli), Klebsiella pneumonia, and Serratia ficaria, reports a 2008 article in CIRI Science.

"Our study also indicated that bacteria can be tracked by shoes over a long distance into your home or personal space after the shoes were contaminated with bacteria," notes Dr. Charles Gerba, the microbiologist who conducted the University of Arizona study. In fact, the study found that the transfer rate from contaminated shoes to previously uncontaminated living spaces was 90 percent to 99 percent.

The good news: Simply washing the shoes is an effective method of significantly reducing the number of bacteria. The University of Arizona study confirmed that machine-washing shoes with detergent eliminated 99 percent of bacteria from the outside of the shoes, and 90 percent of the bacteria from the inside. ABC News made "Kick off your kicks" its No. 1 method of "detoxing your home," suggesting that leaving your shoes at the door will leave 80 percent of certain environmental pollutants -- such as road sealant and pesticides -- outside.