Do plastic bowls harbor more bacteria than steel ones?

Every scratch on a plastic bowl is a microscopic crevice that bacteria can settle into, out of reach of normal washing. Over months of use, chewing, claws and repeated scrubbing add up to a surface riddled with these tiny grooves, even when the bowl still looks fine to the eye.

Stainless steel stays smooth and non porous through years of daily use and handles hot water or a dishwasher cycle without degrading. Glazed ceramic behaves similarly as long as the glaze stays intact, though a chipped or cracked piece can develop the same trapped bacteria problem as scratched plastic.

Visible scratching, a cloudy or dull surface that used to be shiny, or a persistent odor that will not wash out are all signs a plastic bowl has passed the point where cleaning alone can keep bacteria levels reasonable. Replacing it, rather than continuing to deep clean it, is usually the more practical fix at that stage.

Run a fingernail lightly across the inside surface of a plastic bowl: if you can feel or see fine scratch lines, especially near the bottom where a spoon or the dog's teeth make regular contact, that surface is already past the point where washing alone keeps bacteria levels consistently low. A smooth, unscratched surface on a newer plastic bowl is still fine to keep using. Ceramic without any glaze, sometimes used in decorative or handmade bowls, behaves more like plastic in this respect, since the porous unglazed surface can absorb moisture and bacteria in a way a properly glazed piece does not.