A kitchen sponge is not your enemy. But it can be very dirty. Last week, scientists published a study revealing how densely packed your dirty kitchen sponge is with microscopic bacteria. After I wrote an article about their work, readers flooded my inbox with good questions, so I asked around for some answers.

First, let’s examine what the study did and didn’t do.

The study was designed to establish improved measurements of the bacterial populations that live inside this common household item. Previous measurements had mainly looked at those from sponges dirtied in the lab, growing the bacteria in a petri dish. But because not all bacteria will grow in that medium, their numbers may have been underestimated, said Markus Egert, the microbiologist at the University of Furtwangen in Germany who led the study.

“Our study was mainly thought to create awareness, and not fear,” Dr. Egert wrote in a follow-up email.

But what they found alarmed many readers. Although not designed to evaluate disinfection methods, the researchers collected additional data from the sponge donors (a sample of 14 sponges, which the researchers concede was limited). And to their surprise, sponges regularly cleaned in soapy water or the microwave actually harbored more of a bacteria called Moraxella osloensis. This bacteria is generally common and harmless, but it can cause infections in people with compromised immune systems.