They wipe up spills and lather up suds in the shower. With all that sanitizing, sponges should be squeaky-clean, right? Wrong. As you use them, sponges come into contact with some nasty bacteria, which erode their disinfecting abilities. Here’s how to know when you’ve squeezed your sponge dry.

Dish Sponge: If it smells or has loose pieces, throw it away. “Odor signals that food has collected and decomposed inside the sponge,” says Dean Cliver, a professor of food safety at the University of California, Davis. “And when the cleaning surface is damaged, it doesn’t absorb spills or scrub effectively.” Cliver recommends disinfecting a sponge daily or immediately if it has mopped up juice from raw meat. Zap it in the microwave on high for one minute to prevent growth of E. coli and salmonella. To prevent cross-contamination, use a different sponge for dishes, countertops, and bathrooms.

Kitchen-Countertop or Bathroom-Cleaning Sponge: These should last longer than a dish sponge because they are generally used less frequently. Disinfect in the microwave between uses and discard when the sponge surface becomes damaged.

Floor Mop or Toilet Sponge: Replace them if they have snags or loose pieces; in this state, they will just push dirt around. Prolong their life span and ward off mold by disinfecting after each use. Soak in a mixture of one gallon of water and 3/4 cup of bleach for five minutes, recommends Sarah Smock, a spokesperson for Merry Maids, a Memphis-based cleaning service.

Bath and Body Sponge: Discard shower puffs every four to six weeks or immediately if they develop an odor or change color, says Joshua Wieder, a dermatologist in Los Angeles. Natural sponges can retain moisture even if they don’t seem wet. Replace these monthly, says Ava Shamban, a dermatologist and a researcher for the Food and Drug Administration,“so you don’t risk contracting a bacterial or fungal infection.”