Based on the existing research, the jury is still out on whether microwaving sponges is actually beneficial. According to one 2017 study, researchers found microwaving, along with boiling, can significantly reduce the bacterial load of sponges, but that doesn’t mean we should all be doing it.
“Results were contradictory,” the study authors write, “for example showing effectiveness in the laboratory, but not in used kitchen sponges, and no method alone seemed to be able to achieve a general bacterial reduction of more than about 60%.”
This isn’t ideal, they note, hypothesizing that resistant bacteria that survive the sanitation process can rapidly re-colonize (similar to the effect of antibiotics on the gut), which could promote more harmful bacteria in the sponges.
In another study conducted in 2020, researchers note microwaving sponges does appear to alter the composition and metabolic properties of the microbial communities, but more research is needed to determine if those changes are good or bad for our health.