Study finds cleaning your kitchen sponge may not keep it clean

— -- The kitchen sponge you use to wash dishes or clean the counters should be replaced each week, according to a new study.

The study, published online last month in Scientific Reports, also found that sponges that were regularly cleaned by their users did not contain any less bacteria than uncleaned sponges.

“Presumably, resistant bacteria survive the sanitation process and rapidly re–colonize the released niches until reaching a similar abundance as before the treatment,” the study concluded.

The researchers examined 14 sponges collected from private households in Germany in 2012 and seven new sponges purchased in local German stores in 2017. The used sponges had been cleaned by methods including heating in a microwave and rinsing with hot, soapy water.

Researchers found that kitchen sponges “harbor a higher bacterial diversity” than was previously known. Researchers concluded that cleaning sponges could actually make them dirtier, adding that it was "not advisable" to clean them for a prolonged period of time.

“From a long-term perspective, sponge sanitation methods appear not sufficient to effectively reduce the bacterial load in kitchen sponges and might even increase the shares of RG2-related bacteria,” the study said, referring to Risk Group 2, the type of microorganisms that may be associated with human disease.

The researchers recommended changing sponges weekly, however, they did not directly study what effects the frequency of changing out sponges would have.